Digestive System, Diet and Behavior

**139**

horses.

**1. Introduction**

**Chapter 8**

**Abstract**

Approach

Current Strategies for Prevention

Postoperative Ileus: A Multimodal

Equine paralytic (postoperative) ileus generally refers to an acute condition of impaired gastrointestinal motility. Paralytic ileus is most frequently seen following abdominal surgery on the small intestine in horses. Three main mechanisms are involved separately or simultaneously in its causation, namely neurogenicendocrinic, inflammatory-endotoxic and pharmacological mechanisms. Regardless of the cause, equine paralytic ileus can be fatal, if not properly diagnosed and treated. Over the past 22 years (1997–2019), we have diagnosed and treated more than 180 horses with postoperative ileus using differing methods. Based on our results and experience, and that of others, we have developed a multimodal strategy to reduce the incidence of postoperative ileus. This has resulted in effective treatment of ileus-diagnosed patients in 94% of cases, a significant improvement in survival rates over the last 20 years. In this review, we described pre-, intra-, and postoperative multiple supplementary preventative and treatment procedures that cure this condition. These methods are dependent on individual cases but include the control of endotoxemia and inflammation, as well as using the least traumatic surgical techniques, carrying out the pelvic flexure colotomy, improved anesthesia techniques, treating with continuous postoperative peritoneal lavage, the use of fluid, antibiotic and NSAIDs therapy, according to a scheme the use of different prokinetic agents (including metoclopramide, neostigmine methylsulfate and domperidone), nasogastric decompression, management to minimize the surgical and postoperative stress reaction and judicious timing of postoperative feeding of

**Keywords:** postoperative ileus, paralytic ileus, horse, prevention, treatment

Visceral abdominal pain of the horse, defined as equine colic, is one of the most acute life-threatening problems facing equine practitioners [1]. The incidence of equine colic has been reported as between 4 and 10 cases/100 horses/ year [2]. Colic in horses can be caused by more than 70 pathological processes in the gastrointestinal tract and manifests itself in many forms [3]. The diseases that

and Treatment of Equine

*Milomir Kovac, Ruslan Aliev, Sergey Pozyabin,* 

*Nevena Drakul and Albert Rizvanov*

#### **Chapter 8**

## Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal Approach

*Milomir Kovac, Ruslan Aliev, Sergey Pozyabin, Nevena Drakul and Albert Rizvanov*

#### **Abstract**

Equine paralytic (postoperative) ileus generally refers to an acute condition of impaired gastrointestinal motility. Paralytic ileus is most frequently seen following abdominal surgery on the small intestine in horses. Three main mechanisms are involved separately or simultaneously in its causation, namely neurogenicendocrinic, inflammatory-endotoxic and pharmacological mechanisms. Regardless of the cause, equine paralytic ileus can be fatal, if not properly diagnosed and treated. Over the past 22 years (1997–2019), we have diagnosed and treated more than 180 horses with postoperative ileus using differing methods. Based on our results and experience, and that of others, we have developed a multimodal strategy to reduce the incidence of postoperative ileus. This has resulted in effective treatment of ileus-diagnosed patients in 94% of cases, a significant improvement in survival rates over the last 20 years. In this review, we described pre-, intra-, and postoperative multiple supplementary preventative and treatment procedures that cure this condition. These methods are dependent on individual cases but include the control of endotoxemia and inflammation, as well as using the least traumatic surgical techniques, carrying out the pelvic flexure colotomy, improved anesthesia techniques, treating with continuous postoperative peritoneal lavage, the use of fluid, antibiotic and NSAIDs therapy, according to a scheme the use of different prokinetic agents (including metoclopramide, neostigmine methylsulfate and domperidone), nasogastric decompression, management to minimize the surgical and postoperative stress reaction and judicious timing of postoperative feeding of horses.

**Keywords:** postoperative ileus, paralytic ileus, horse, prevention, treatment

#### **1. Introduction**

Visceral abdominal pain of the horse, defined as equine colic, is one of the most acute life-threatening problems facing equine practitioners [1]. The incidence of equine colic has been reported as between 4 and 10 cases/100 horses/ year [2]. Colic in horses can be caused by more than 70 pathological processes in the gastrointestinal tract and manifests itself in many forms [3]. The diseases that accompany colic in horse are often characterized by ileus. The Greek physician Soranus defined an ileus as "a severe and dangerous twisting of the intestines." Currently, an ileus can be referred to as a symptom characterized by a complete or partial disturbance passage of contents through the intestinal canal, due to obturation, strangulation, spasm, ischemia, adhesions and impaired motor function (paralytic ileus) [4].

The definition of paralytic ileus is somewhat controversial. Paralytic ileus is mostly defined as a temporary or permanent cessation of propulsive contractions of the gastrointestinal tract, irrespective of pathogenetic mechanisms, with subsequent gut dilation and accumulation of secretions and gas within its lumen [5]. Paralytic ileus in the horse is not a primary disorder but rather an underlying cause and can be classified on the basis of its etiology. More than 95% of all paralytic ileus cases in horses, seen after abdominal surgery, are primarily in the small intestine [6, 7]. Precisely for this reason, the paralytic ileus is often signified as postoperative ileus (POI). Once in a while, equine POI can be classified more precisely according to anatomical localization, for instance POI of the small intestine or POI of the cecum and colon. POI of the small intestine is easy to diagnose, through the presence of gastric reflux (i.a.), and impaired motor function seldom occurs in other parts of the gastrointestinal tract in horses too [8]. In the latter rarer cases, diagnosis is more of a challenge, because the presence of gastric reflux in the postoperative period is relatively uncommon after surgery on the large intestine in horses [9]. However, it must be considered also that the dysmotility in equine POI of small intestine may mask large intestine involvement.

In people following surgery, the return of the small intestine's action generally begins around 4–8 h postoperatively and generally completes in around 24 h [10]. The colon resumes its function between 48 and 72 h postoperatively [11, 12]. In humans, based on this observation, various additional qualifying terms have been applied to POI, such as physiological POI, prolonged POI and recurrent POI [13]. This classification system can also be applied to horses, but it must be emphasized that the recurrent form of POI is very rare [14].

Regardless of determination or classification, equine paralytic ileus is a common and serious complication of surgery associated with highly increased odds of death. Reported fatality rate in horses with POI also varies widely, from 13 to 86% [15–18]. In one study, horses that developed postoperative ileus were nearly 30 times less likely to survive than horses that did not develop ileus [19]. Additionally, equine POI leads to increased hospitalization time and treatment costs. It is for these reasons that since the first modern attempts to undertake abdominal surgery 50 years ago through to today, prevention and treatment of POI are widely discussed topics in equine medicine [20, 21]. In human medicine, enhanced recovery after surgery (ERAS) programs exist, which include multiple pre-, intra- and postoperative interventions, aiming to reduce the occurrence of POI [22]. Currently, in equine medicine, no universally-accepted approach exists for the management of equine POI.

Over the past 22 years, we have diagnosed and treated more than 180 horses with POI, using, in two veterinary clinics "Hochmoor" (Germany, 1997–2007) and "New Century" in Moskow (Russia, 2007–2019). In the latter times, with multiple pre-, intra- and postoperative procedures, not only was POI prevalence reduced significantly, but also following occurrences of equine POI successful treatment and survival were possible in more than 94% of cases. The purpose of this chapter review is to clarify some of the proposed key mechanisms in the pathophysiology of POI, share our experiences and make proposals for the prevention and treatment of equine POI.

**141**

peptide) [30].

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal…*

An appreciation of the basic mechanisms that regulate gastrointestinal motility is a key component to understanding paralytic ileus. The musculature of the gastrointestinal tract in horses is made up of smooth muscle cells that are intimately associated, thus allowing them to conduct electrophysiological functions. There are three distinctive electrical potentials in the equine intestine: resting potential, slow-wave and spike potential that trigger contractions. Slow waves are rhythmic pacemaker currents initiated by the interstitial cells of Cajal (ICC). Normal gastrointestinal motility in horses results from very complex interactions among the enteric nervous system (ENS), autonomic and central nervous systems, ICC, gastrointestinal hormones, immune cells, glial cells and local factors that affect smooth-muscle activity [21, 23–25]. Extrinsically, the sympathetic nervous input through noradrenaline has an inhibitory effect on gastrointestinal motility, whereas parasympathetic input increases motility. The ENS is involved in all aspects of gastrointestinal function, not only motility, as well as by enteric processes such as immune responses, detecting nutrients, microvascular circulation, intestinal barrier function, and epithelial secretion of fluids and ions [10]. The neurons of the ENS are collected into two types of ganglia: myenteric (Auerbach's) and submucosal (Meissner's) plexuses. The enteric nervous system influences the gastrointestinal tract either directly through neurotransmitters or indirectly through intermediate cells, such as the ICC, cells of the immune system or endocrine cells [10]. These intestinal neurons communicate through more than 25 different neurotransmitters, including stimulatory neurotransmitters (acetylcholine, neurokinin A, adenosine, substance P, motilin, serotonin and cholecystokinin) and inhibitory neurotransmitters, for instance, vasoactive intestinal peptide (VIP), nitrous oxide (NO), neuropeptide Y, calcitonin gene-related peptide, GABA and neurotensin [26–29]. The endocrine system also indirectly affects regulation of the gastrointestinal tract motility. The hormones related to stress activity (glucocorticoids, cortico-realizing peptide, thyroid hormones and somatotropic hormone) have the most pronounced inhibitory effect on gastrointestinal tract activity. Additionally, the intestinal cells produce a range of hormones and hormone-like substances, some of which are also neurotransmitters. These substances regulate the motility of the gastrointestinal tract (motilin, enteroglucagon, cholecystokinin, pancreatic polypeptide and peptide YY) and secretory activity (gastrin, secretin, cholecystokinin, pancreatic polypeptide, gastric inhibitory peptide and neurotensin) and also regulate the production of other hormonal substances (somatostatin and gastrin-releasing

**2. Normal physiology of equine gastrointestinal motility**

**3. Prevalence and risk factors for equine postoperative ileus**

The etiology of paralytic ileus in the horse is multifactorial, and various factors contribute either simultaneously or at various times during the development of this entity. In the current literature, the incidence of POI in horses undergoing surgical treatment of all types of colic has been reported to range from 10 to 21% [31–33]. The incidence of POI in horses undergoing surgical treatment for small intestine lesions varies widely from 10 to 73% [1, 15, 16, 18–20, 31, 34–38]. The large variation in the reported rates can be at least partly explained by the criteria used to define postoperative ileus. Other forms of paralytic ileus, those that do not present due to equine surgery, are much less common than in humans. These include forms that result from metabolic derangements, acid-base abnormalities, electrolyte

*DOI: http://dx.doi.org/10.5772/intechopen.91290*

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal… DOI: http://dx.doi.org/10.5772/intechopen.91290*

#### **2. Normal physiology of equine gastrointestinal motility**

An appreciation of the basic mechanisms that regulate gastrointestinal motility is a key component to understanding paralytic ileus. The musculature of the gastrointestinal tract in horses is made up of smooth muscle cells that are intimately associated, thus allowing them to conduct electrophysiological functions. There are three distinctive electrical potentials in the equine intestine: resting potential, slow-wave and spike potential that trigger contractions. Slow waves are rhythmic pacemaker currents initiated by the interstitial cells of Cajal (ICC). Normal gastrointestinal motility in horses results from very complex interactions among the enteric nervous system (ENS), autonomic and central nervous systems, ICC, gastrointestinal hormones, immune cells, glial cells and local factors that affect smooth-muscle activity [21, 23–25]. Extrinsically, the sympathetic nervous input through noradrenaline has an inhibitory effect on gastrointestinal motility, whereas parasympathetic input increases motility. The ENS is involved in all aspects of gastrointestinal function, not only motility, as well as by enteric processes such as immune responses, detecting nutrients, microvascular circulation, intestinal barrier function, and epithelial secretion of fluids and ions [10]. The neurons of the ENS are collected into two types of ganglia: myenteric (Auerbach's) and submucosal (Meissner's) plexuses. The enteric nervous system influences the gastrointestinal tract either directly through neurotransmitters or indirectly through intermediate cells, such as the ICC, cells of the immune system or endocrine cells [10]. These intestinal neurons communicate through more than 25 different neurotransmitters, including stimulatory neurotransmitters (acetylcholine, neurokinin A, adenosine, substance P, motilin, serotonin and cholecystokinin) and inhibitory neurotransmitters, for instance, vasoactive intestinal peptide (VIP), nitrous oxide (NO), neuropeptide Y, calcitonin gene-related peptide, GABA and neurotensin [26–29]. The endocrine system also indirectly affects regulation of the gastrointestinal tract motility. The hormones related to stress activity (glucocorticoids, cortico-realizing peptide, thyroid hormones and somatotropic hormone) have the most pronounced inhibitory effect on gastrointestinal tract activity. Additionally, the intestinal cells produce a range of hormones and hormone-like substances, some of which are also neurotransmitters. These substances regulate the motility of the gastrointestinal tract (motilin, enteroglucagon, cholecystokinin, pancreatic polypeptide and peptide YY) and secretory activity (gastrin, secretin, cholecystokinin, pancreatic polypeptide, gastric inhibitory peptide and neurotensin) and also regulate the production of other hormonal substances (somatostatin and gastrin-releasing peptide) [30].

#### **3. Prevalence and risk factors for equine postoperative ileus**

The etiology of paralytic ileus in the horse is multifactorial, and various factors contribute either simultaneously or at various times during the development of this entity. In the current literature, the incidence of POI in horses undergoing surgical treatment of all types of colic has been reported to range from 10 to 21% [31–33]. The incidence of POI in horses undergoing surgical treatment for small intestine lesions varies widely from 10 to 73% [1, 15, 16, 18–20, 31, 34–38]. The large variation in the reported rates can be at least partly explained by the criteria used to define postoperative ileus. Other forms of paralytic ileus, those that do not present due to equine surgery, are much less common than in humans. These include forms that result from metabolic derangements, acid-base abnormalities, electrolyte

*Equine Science*

(paralytic ileus) [4].

intestine may mask large intestine involvement.

that the recurrent form of POI is very rare [14].

accompany colic in horse are often characterized by ileus. The Greek physician Soranus defined an ileus as "a severe and dangerous twisting of the intestines." Currently, an ileus can be referred to as a symptom characterized by a complete or partial disturbance passage of contents through the intestinal canal, due to obturation, strangulation, spasm, ischemia, adhesions and impaired motor function

The definition of paralytic ileus is somewhat controversial. Paralytic ileus is mostly defined as a temporary or permanent cessation of propulsive contractions of the gastrointestinal tract, irrespective of pathogenetic mechanisms, with subsequent gut dilation and accumulation of secretions and gas within its lumen [5]. Paralytic ileus in the horse is not a primary disorder but rather an underlying cause and can be classified on the basis of its etiology. More than 95% of all paralytic ileus cases in horses, seen after abdominal surgery, are primarily in the small intestine [6, 7]. Precisely for this reason, the paralytic ileus is often signified as postoperative ileus (POI). Once in a while, equine POI can be classified more precisely according to anatomical localization, for instance POI of the small intestine or POI of the cecum and colon. POI of the small intestine is easy to diagnose, through the presence of gastric reflux (i.a.), and impaired motor function seldom occurs in other parts of the gastrointestinal tract in horses too [8]. In the latter rarer cases, diagnosis is more of a challenge, because the presence of gastric reflux in the postoperative period is relatively uncommon after surgery on the large intestine in horses [9]. However, it must be considered also that the dysmotility in equine POI of small

In people following surgery, the return of the small intestine's action generally begins around 4–8 h postoperatively and generally completes in around 24 h [10]. The colon resumes its function between 48 and 72 h postoperatively [11, 12]. In humans, based on this observation, various additional qualifying terms have been applied to POI, such as physiological POI, prolonged POI and recurrent POI [13]. This classification system can also be applied to horses, but it must be emphasized

Regardless of determination or classification, equine paralytic ileus is a common and serious complication of surgery associated with highly increased odds of death. Reported fatality rate in horses with POI also varies widely, from 13 to 86% [15–18]. In one study, horses that developed postoperative ileus were nearly 30 times less likely to survive than horses that did not develop ileus [19]. Additionally, equine POI leads to increased hospitalization time and treatment costs. It is for these reasons that since the first modern attempts to undertake abdominal surgery 50 years ago through to today, prevention and treatment of POI are widely discussed topics in equine medicine [20, 21]. In human medicine, enhanced recovery after surgery (ERAS) programs exist, which include multiple pre-, intra- and postoperative interventions, aiming to reduce the occurrence of POI [22]. Currently, in equine medicine, no universally-accepted approach exists for the management of

Over the past 22 years, we have diagnosed and treated more than 180 horses with POI, using, in two veterinary clinics "Hochmoor" (Germany, 1997–2007) and "New Century" in Moskow (Russia, 2007–2019). In the latter times, with multiple pre-, intra- and postoperative procedures, not only was POI prevalence reduced significantly, but also following occurrences of equine POI successful treatment and survival were possible in more than 94% of cases. The purpose of this chapter review is to clarify some of the proposed key mechanisms in the pathophysiology of POI, share our experiences and make proposals for the prevention and treatment of

**140**

equine POI.

equine POI.

imbalances (hypokalemia and hypocalcemia), severity stress syndrome, peritonitis, bacterial infection, uremia, hypoalbuminemia, abdominal trauma, burns, botulism, grass sickness, atrophic visceral myopathy and application of drugs and anesthetic agents [6, 7, 26, 32].

According to our investigation, there was no significant age or breed dependence associated with the incidence of postoperative ileus in horses, but stallions more often had POI than geldings [39]. Our observations showed that the horses with a so-called hot temperament (i.e., horses with more excitable demeanors) had increased risks of developing POI than warm- or cold-blooded horses. The preliminary results (unpublished data) also showed that horses with behavioral symptoms of stress and high concentrations of cortisol in their blood in the pre- and postoperative time more often had POI than horses with normal concentrations of cortisol.

According to our observations, if pre- and during surgical intervention the equine jejunum had a high degree of intraluminal distension (more than 8 cm), postoperative ileus was more likely to occur and did so in more than 70% of the cases observed [32]. This is partly confirmed by other authors [15, 18]. A possible reason for this finding is the long onset of colic disease and high degree of endotoxic shock, which leads to enteric nervous system damage and a high degree of intraluminal jejunum distension. It has been demonstrated that decreases in intestinal motility through the distension of equine jejunum are partly due to decreases in motilin receptor synthesis [21].

Horses with small intestinal strangulating obstruction (for instance, by hernia inguinalis, entrapment in foramen omentalis) are at increased risk of developing POI, compared with obstructive ileus (for instance, by ileum or jejunum obstipation) [40, 41]. A basis for higher concentration endotoxins is that horses with entrapment in the foramen omentalis have lower blood pressures during abdominal surgery than horses with ileum obstipation [42]. It has also been shown that horses suffering from pedunculated lipoma obstruction are three times more likely to suffer from POI when compared with horses suffering from other intestinal pathologies [3]. This fact was confirmed in our own observations [4]. Many factors are associated with increased risk of POI in horses with pedunculated lipoma obstruction, for instance age-related decreases in intestinal density of the enteric neurons and glial cells, rapidly developing endotoxic shock and perhaps also high colic pain, which lead to enormous activation of the sympathetic nervous system.

Numerous studies have shown that long duration of colic disease, with evidence of endotoxin shock (high pulse rate and hemoconcentration), the presence of >8 l of reflux at admission, anesthesia for longer than 2.5 h, and the performance of a small intestinal resections pose enormous risks for POI development [15, 31, 43, 44]. Based on our results, the risk of developing POI and other fatal complications were associated with increased duration of surgery [14]. Surgical techniques also affect the incidence of POI in horses. The ability to perform a safe bowel resection and anastomosis techniques also affects the incidence of POI in horses; for instance, the use of jejunocecostomy has been associated more often with the development of POI when compared to horses in which end-to-end jejunostomy is performed [45]. One possible reason for this fact is possibly that the end-end jejunostomy is done more rapidly, and therefore duration of surgery and anesthesia is shorter than by the jejunocecostomy.

Other postoperative complications such as primarily postanesthetic myopathy and peritonitis increased the rapid risk of POI development in horses [46]. Other postoperative complications after colic surgery for example incisional infection, herniation and dehiscence, jugular vein thrombophlebitis, laminitis, adhesions and

**143**

**Figure 1.**

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal…*

diarrhea had no important influence on the development of POI; however, these complications tend to develop later during the postoperative period in horses [39].

The pathogenesis of postoperative ileus is complex, with multiple factors contributing either simultaneously or at various times during the development of this entity. The classical view in the pathogenesis of POI involves two phases: an initial neurogenic phase resulting in immediate postoperative impairment of intestinal motility and a subsequent inflammatory phase lasting for several days [24, 30, 37, 47]. On the basis of our observations, we expanded this view into three (or five) main mechanisms, which either independently or in combination are involved in the causation of equine postoperative ileus, namely inflammatory-endotoxic mechanism, neurogenendocrinic mechanism and pharmacological-anesthetic mechanisms. However, the importance of each contributing mechanism may vary over time, with considerable

Postoperative inflammation of the small intestine (and nearly imperceptibly of equine large intestine) is an important factor in the pathophysiology of equine POI [9, 48]. It is well known that inflammation is a biological response of the immune system, blood vessels and molecular mediators to a broad range of different stimuli such as pathogens, endotoxins, and physical and chemical irritants. There are a lot of inflammatory agents to take into consideration in POI, for instance, specific intestinal pathology and tissue injury (including obturation, strangulation and adhesion), bacteria, endotoxins, surgical trauma and manipulation [49–53]. The classical intestinal inflammation following paralytic ileus occurs by the duodenitisproximal jejunitis (DPJ). This syndrome is caused primarily by toxic and infectious

Horses with strangulating lesions of the small intestine have been shown to have various degrees of serosal and neuromuscular inflammation and high numbers of apoptotic cells (including smooth muscle, enteric neurons and glia), possibly due to intestinal ischemia and reperfusion injury [23, 54–57]. According to different studies, equine POI might actually be triggered by a primary disturbance of the smooth muscles' ability to contract, and how the number of smooth muscles or

*Histological appearance of the jejunum in a horse affected by postoperative ileus. Note the mucous membrane maintaining its correct structure. In the submucosal layer and on the border with the inner muscle, extensive delaminating hemorrhage and leukocyte reaction were determined. Muscle fibers of the inner muscle layer with pronounced dystrophic changes in the cytoplasm were present. Ganglion cells in the intramuscular layer were not detected; in their place, a loose, weakly basophilic fibrous connective tissue with single mononuclear cells* 

*was present. The serosa was moderately edematous. H&E stained, ×10 magnification.*

overlap and possible interactions; therefore, this division is conditional.

*DOI: http://dx.doi.org/10.5772/intechopen.91290*

**4. Pathophysiology of equine postoperative ileus**

**4.1 The role of inflammation and endotoxemia**

agents (e.g., Salmonella and *Clostridium perfringens*) [4, 44].

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal… DOI: http://dx.doi.org/10.5772/intechopen.91290*

diarrhea had no important influence on the development of POI; however, these complications tend to develop later during the postoperative period in horses [39].

#### **4. Pathophysiology of equine postoperative ileus**

The pathogenesis of postoperative ileus is complex, with multiple factors contributing either simultaneously or at various times during the development of this entity. The classical view in the pathogenesis of POI involves two phases: an initial neurogenic phase resulting in immediate postoperative impairment of intestinal motility and a subsequent inflammatory phase lasting for several days [24, 30, 37, 47]. On the basis of our observations, we expanded this view into three (or five) main mechanisms, which either independently or in combination are involved in the causation of equine postoperative ileus, namely inflammatory-endotoxic mechanism, neurogenendocrinic mechanism and pharmacological-anesthetic mechanisms. However, the importance of each contributing mechanism may vary over time, with considerable overlap and possible interactions; therefore, this division is conditional.

#### **4.1 The role of inflammation and endotoxemia**

Postoperative inflammation of the small intestine (and nearly imperceptibly of equine large intestine) is an important factor in the pathophysiology of equine POI [9, 48]. It is well known that inflammation is a biological response of the immune system, blood vessels and molecular mediators to a broad range of different stimuli such as pathogens, endotoxins, and physical and chemical irritants. There are a lot of inflammatory agents to take into consideration in POI, for instance, specific intestinal pathology and tissue injury (including obturation, strangulation and adhesion), bacteria, endotoxins, surgical trauma and manipulation [49–53]. The classical intestinal inflammation following paralytic ileus occurs by the duodenitisproximal jejunitis (DPJ). This syndrome is caused primarily by toxic and infectious agents (e.g., Salmonella and *Clostridium perfringens*) [4, 44].

Horses with strangulating lesions of the small intestine have been shown to have various degrees of serosal and neuromuscular inflammation and high numbers of apoptotic cells (including smooth muscle, enteric neurons and glia), possibly due to intestinal ischemia and reperfusion injury [23, 54–57]. According to different studies, equine POI might actually be triggered by a primary disturbance of the smooth muscles' ability to contract, and how the number of smooth muscles or

#### **Figure 1.**

*Equine Science*

cortisol.

anesthetic agents [6, 7, 26, 32].

motilin receptor synthesis [21].

imbalances (hypokalemia and hypocalcemia), severity stress syndrome, peritonitis, bacterial infection, uremia, hypoalbuminemia, abdominal trauma, burns, botulism, grass sickness, atrophic visceral myopathy and application of drugs and

According to our investigation, there was no significant age or breed dependence associated with the incidence of postoperative ileus in horses, but stallions more often had POI than geldings [39]. Our observations showed that the horses with a so-called hot temperament (i.e., horses with more excitable demeanors) had increased risks of developing POI than warm- or cold-blooded horses. The preliminary results (unpublished data) also showed that horses with behavioral symptoms of stress and high concentrations of cortisol in their blood in the pre- and postoperative time more often had POI than horses with normal concentrations of

According to our observations, if pre- and during surgical intervention the equine jejunum had a high degree of intraluminal distension (more than 8 cm), postoperative ileus was more likely to occur and did so in more than 70% of the cases observed [32]. This is partly confirmed by other authors [15, 18]. A possible reason for this finding is the long onset of colic disease and high degree of endotoxic shock, which leads to enteric nervous system damage and a high degree of intraluminal jejunum distension. It has been demonstrated that decreases in intestinal motility through the distension of equine jejunum are partly due to decreases in

Horses with small intestinal strangulating obstruction (for instance, by hernia inguinalis, entrapment in foramen omentalis) are at increased risk of developing POI, compared with obstructive ileus (for instance, by ileum or jejunum obstipation) [40, 41]. A basis for higher concentration endotoxins is that horses with entrapment in the foramen omentalis have lower blood pressures during abdominal surgery than horses with ileum obstipation [42]. It has also been shown that horses suffering from pedunculated lipoma obstruction are three times more likely to suffer from POI when compared with horses suffering from other intestinal pathologies [3]. This fact was confirmed in our own observations [4]. Many factors are associated with increased risk of POI in horses with pedunculated lipoma obstruction, for instance age-related decreases in intestinal density of the enteric neurons and glial cells, rapidly developing endotoxic shock and perhaps also high colic pain, which lead to enormous activation of the sympathetic nervous system. Numerous studies have shown that long duration of colic disease, with evidence of endotoxin shock (high pulse rate and hemoconcentration), the presence of >8 l of reflux at admission, anesthesia for longer than 2.5 h, and the performance of a small intestinal resections pose enormous risks for POI development [15, 31, 43, 44]. Based on our results, the risk of developing POI and other fatal complications were associated with increased duration of surgery [14]. Surgical techniques also affect the incidence of POI in horses. The ability to perform a safe bowel resection and anastomosis techniques also affects the incidence of POI in horses; for instance, the use of jejunocecostomy has been associated more often with the development of POI when compared to horses in which end-to-end jejunostomy is performed [45]. One possible reason for this fact is possibly that the end-end jejunostomy is done more rapidly, and therefore duration of surgery and anesthesia is shorter than by the

Other postoperative complications such as primarily postanesthetic myopathy and peritonitis increased the rapid risk of POI development in horses [46]. Other postoperative complications after colic surgery for example incisional infection, herniation and dehiscence, jugular vein thrombophlebitis, laminitis, adhesions and

**142**

jejunocecostomy.

*Histological appearance of the jejunum in a horse affected by postoperative ileus. Note the mucous membrane maintaining its correct structure. In the submucosal layer and on the border with the inner muscle, extensive delaminating hemorrhage and leukocyte reaction were determined. Muscle fibers of the inner muscle layer with pronounced dystrophic changes in the cytoplasm were present. Ganglion cells in the intramuscular layer were not detected; in their place, a loose, weakly basophilic fibrous connective tissue with single mononuclear cells was present. The serosa was moderately edematous. H&E stained, ×10 magnification.*

neural receptors has changed through a leukocytic and macrophage inflammatory response, primarily within the intestinal muscularis externa (**Figure 1**) [58–60]. Potentially due to different inhibitory mediators (NO, SP, VIP and NPY), cytokines (TNF, IL-1b, IL-6 and IL-10), monocyte chemotactic protein-1, prostaglandins, histamine, mast cell proteinase-1, tryptase, reactive oxygen intermediates, defensins and adenosine secreted from the muscularis externa during intestinal inflammation and abdominal surgery [49, 61–64]. This local molecular inflammatory response increases prostaglandin E2 levels in the peritoneal cavity that correlates temporally with the development of postoperative ileus [13, 65, 66]. According to our former investigations, in most cases of equine abdominal surgery, during three postoperative days, the concentration of leukocytes is markedly increased (sometimes up to 100 × 109 /l) as are total plasma proteins in the peritoneal cavity [39]. In the horse, postoperative neutrophilic and eosinophilic inflammation of the jejunum has been identified up to 18 h postoperatively [55, 67].

In intestinal inflammation, pathogen-associated molecular patterns or PAMPs have important roles. These molecules can be referred to as small molecular motifs conserved within a class of microbes. Bacterial lipopolysaccharides or endotoxins found on the cell membranes of Gram-negative bacteria are considered to be the prototypical class of PAMPs. The endotoxins are very potent and are widely spread inflammation-inducing substances. One of the basic characteristics of almost all gastrointestinal disorders in horses (primarily by different forms of strangulation ileus) is the development of the endotoxic shock [68]. The mucosal barrier of the equine intestine normally efficiently restricts the transmural movement of endotoxins and bacteria. However, whenever the integrity of the mucosal barrier is lost, as occurs with inflammation or ischemia of the intestinal wall, endotoxins cross into the portal blood and peritoneal cavity [69]. The generally accepted scheme for endotoxin binding is to CD14-bearing receptor cells (monocytes, macrophages, dendritic cells, and possibly vascular endothelial cells), which then associates with the TLR4-MD-2 complex to initiate a downstream signal, causing a proinflammatory response, such as leukocyte recruitment [53]. Macrophage-derived cytokines (such as IL-1b and TNF), as well as arachidonic acid metabolites (i.e., prostacyclin and thromboxane), are responsible for many of the pathophysiologic consequences of endotoxemia and tissue injury in equine colic cases. Endotoxins among other things activate inducible nitric oxide synthase (iNOS) in intestinal macrophages [66]. The resultant increase in NO release stimulates decreased smooth muscle contractility. In healthy ponies, IV infusion of endotoxin also resulted in inhibition of motility in the stomach, cecum, left dorsal colon, and small colon [70]. However, no nasogastric reflux was observed. Although motility in the small intestine was increased, its myoelectric pattern was abnormal. The effects of endotoxins on motility were partially mediated by PGE2 possibly stimulating alpha-2 adrenergic receptors [28, 51, 71]. A platelet-activating factor (PAF) antagonist suppressed some of the endotoxin-induced inhibition of motility in horses. These findings led to the conclusion that the PAF may also play a role in the development of POI [68].

The degree of endotoxic shock in horses is directly dependent on the forms and time span of gastrointestinal disease [72]. As the concentration of Gram-negative bacteria is highest in the large intestine of horses, the release of endotoxin and development of endotoxic shock are logically expected in pathologies of this part of the gastrointestinal tract, for instance by volvulus or colitis [43]. In the small intestine of horses, different population of Gram-negative bacteria exist, but in lower concentrations than observed in the large intestine. It would therefore be expected that in this case the endotoxins would not play a decisive role in development of POI. In contrast to this theory in one study of colic cases, the highest endotoxin concentrations were found in horses with entrapment in the foramen omentalis,

**145**

intestinal tract.

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal…*

pedunculated lipoma obstruction and volvulus (torsion) of the large colon [72]. A significant impairment of small intestine transit has been shown in a rat model of colonic manipulation, which occurred even when the small intestine was surgically isolated [73]. These findings led to the conclusion that colonic manipulation induces an inflammatory response in the muscularis of the small intestine that is initiated

One potential trigger for intestinal inflammation not only endotoxins, as well the damage-associated molecular patterns (DAMPs) which realase by extensive surgical intestinal manipulation, luminale distension and resection [6, 7, 48, 52]. DAMPs are host biomolecules that can initiate a noninfectious inflammatory response. DAMPs are mostly cytosolic proteins and materials derived from the extracellular matrix (including hyaluronan fragments, ATP and heparin sulfate) and are generated following tissue injury [6, 7]. An activation of resident muscularis macrophages in the small intestine through DAMPs results in recruitment of intracellular signaling pathways (p38, JNK/SAP) and the release of pro-inflammatory cytokines [6, 7, 37]. Inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) upregulation then facilitates the production of NO and prostaglandins, both of which impair the contractile activity of the small intestine [52, 74, 75]. It additionally reduces lymphatic drainage with the occurrence of intestinal edema, which further impairs intestinal motility [76].

The sympathetic division of the autonomic nervous system maintains internal

organ homeostasis and initiates the stress response. In addition, sympathetic (adrenergic) hyperactivity results in the reduction of propulsive intestinal motility [8, 77, 78]. In the early component of ileus, the sympathetic neural pathways are activated already in the preoperative period, primarily through intestinal distension or strangulation (i.e., through initial colic pain), but inflammation and surgical manipulation and incision of the intestines and abdomen wall additionally stimulate afferent nerve fibers that subsequently activate peripheral, spinal and/or supraspinal reflex pathways [8, 15, 24, 27]. The sympathetic hyperactivity is amplified through various preoperative stressors (i.e., transport to clinic, unfamiliar surroundings with unknown caretakers, restraint of the horse for examination and rectal investigation) and also in the postoperative period of horse, initially by the recovery from anesthesia, but also in many postoperative diagnostic and management procedures (such as tying in stall, fasting, gastric decompression and blood collection) [24, 79]. There is overwhelming experimental and clinical evidence that

different stress paradigms influence gastrointestinal motility [47, 80–82].

Sympathetic hyperactivity in horse primarily depends on the intensity of the nociceptive (pain) receptor stimulus [83]. Numerous nociceptors of sensory intestinal neurons by tissue damage or surgical manipulation send signals to the spinal cord and further to specific hypothalamic and pontine-medullary neurons. Within this pathway, corticotropin-releasing factor (CRF) plays a central role in inhibiting gastric and small intestinal motor function (but not of the colon) via interaction with the CRF-R2 receptors [82, 84–88]. The CRF stimulates neurons in the supraoptic nucleus of the hypothalamus, which send projections to the spinal cord, including the intermediolateral column of the thoracic cord, where sympathetic preganglionic neurons are located [88, 89]. At this point, inhibitory sympathetic efferent neurons are activated. Norepinephrine is released by sympathetic neurons at the enteric ganglia, which inhibit the release of the excitatory neurotransmitter acetylcholine by stimulating α2-receptors located presynaptically on cholinergic neurons [21]. This causes a depression of smooth muscle contractions in the gastro-

and maintained by the release of endotoxins from the colon.

**4.2 The role of the neurogen-endocrinic factors**

*DOI: http://dx.doi.org/10.5772/intechopen.91290*

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal… DOI: http://dx.doi.org/10.5772/intechopen.91290*

pedunculated lipoma obstruction and volvulus (torsion) of the large colon [72]. A significant impairment of small intestine transit has been shown in a rat model of colonic manipulation, which occurred even when the small intestine was surgically isolated [73]. These findings led to the conclusion that colonic manipulation induces an inflammatory response in the muscularis of the small intestine that is initiated and maintained by the release of endotoxins from the colon.

One potential trigger for intestinal inflammation not only endotoxins, as well the damage-associated molecular patterns (DAMPs) which realase by extensive surgical intestinal manipulation, luminale distension and resection [6, 7, 48, 52]. DAMPs are host biomolecules that can initiate a noninfectious inflammatory response. DAMPs are mostly cytosolic proteins and materials derived from the extracellular matrix (including hyaluronan fragments, ATP and heparin sulfate) and are generated following tissue injury [6, 7]. An activation of resident muscularis macrophages in the small intestine through DAMPs results in recruitment of intracellular signaling pathways (p38, JNK/SAP) and the release of pro-inflammatory cytokines [6, 7, 37]. Inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) upregulation then facilitates the production of NO and prostaglandins, both of which impair the contractile activity of the small intestine [52, 74, 75]. It additionally reduces lymphatic drainage with the occurrence of intestinal edema, which further impairs intestinal motility [76].

#### **4.2 The role of the neurogen-endocrinic factors**

The sympathetic division of the autonomic nervous system maintains internal organ homeostasis and initiates the stress response. In addition, sympathetic (adrenergic) hyperactivity results in the reduction of propulsive intestinal motility [8, 77, 78]. In the early component of ileus, the sympathetic neural pathways are activated already in the preoperative period, primarily through intestinal distension or strangulation (i.e., through initial colic pain), but inflammation and surgical manipulation and incision of the intestines and abdomen wall additionally stimulate afferent nerve fibers that subsequently activate peripheral, spinal and/or supraspinal reflex pathways [8, 15, 24, 27]. The sympathetic hyperactivity is amplified through various preoperative stressors (i.e., transport to clinic, unfamiliar surroundings with unknown caretakers, restraint of the horse for examination and rectal investigation) and also in the postoperative period of horse, initially by the recovery from anesthesia, but also in many postoperative diagnostic and management procedures (such as tying in stall, fasting, gastric decompression and blood collection) [24, 79]. There is overwhelming experimental and clinical evidence that different stress paradigms influence gastrointestinal motility [47, 80–82].

Sympathetic hyperactivity in horse primarily depends on the intensity of the nociceptive (pain) receptor stimulus [83]. Numerous nociceptors of sensory intestinal neurons by tissue damage or surgical manipulation send signals to the spinal cord and further to specific hypothalamic and pontine-medullary neurons. Within this pathway, corticotropin-releasing factor (CRF) plays a central role in inhibiting gastric and small intestinal motor function (but not of the colon) via interaction with the CRF-R2 receptors [82, 84–88]. The CRF stimulates neurons in the supraoptic nucleus of the hypothalamus, which send projections to the spinal cord, including the intermediolateral column of the thoracic cord, where sympathetic preganglionic neurons are located [88, 89]. At this point, inhibitory sympathetic efferent neurons are activated. Norepinephrine is released by sympathetic neurons at the enteric ganglia, which inhibit the release of the excitatory neurotransmitter acetylcholine by stimulating α2-receptors located presynaptically on cholinergic neurons [21]. This causes a depression of smooth muscle contractions in the gastrointestinal tract.

*Equine Science*

100 × 109

identified up to 18 h postoperatively [55, 67].

neural receptors has changed through a leukocytic and macrophage inflammatory response, primarily within the intestinal muscularis externa (**Figure 1**) [58–60]. Potentially due to different inhibitory mediators (NO, SP, VIP and NPY), cytokines (TNF, IL-1b, IL-6 and IL-10), monocyte chemotactic protein-1, prostaglandins, histamine, mast cell proteinase-1, tryptase, reactive oxygen intermediates, defensins and adenosine secreted from the muscularis externa during intestinal inflammation and abdominal surgery [49, 61–64]. This local molecular inflammatory response increases prostaglandin E2 levels in the peritoneal cavity that correlates temporally with the development of postoperative ileus [13, 65, 66]. According to our former investigations, in most cases of equine abdominal surgery, during three postoperative days, the concentration of leukocytes is markedly increased (sometimes up to

/l) as are total plasma proteins in the peritoneal cavity [39]. In the horse,

postoperative neutrophilic and eosinophilic inflammation of the jejunum has been

In intestinal inflammation, pathogen-associated molecular patterns or PAMPs have important roles. These molecules can be referred to as small molecular motifs conserved within a class of microbes. Bacterial lipopolysaccharides or endotoxins found on the cell membranes of Gram-negative bacteria are considered to be the prototypical class of PAMPs. The endotoxins are very potent and are widely spread inflammation-inducing substances. One of the basic characteristics of almost all gastrointestinal disorders in horses (primarily by different forms of strangulation ileus) is the development of the endotoxic shock [68]. The mucosal barrier of the equine intestine normally efficiently restricts the transmural movement of endotoxins and bacteria. However, whenever the integrity of the mucosal barrier is lost, as occurs with inflammation or ischemia of the intestinal wall, endotoxins cross into the portal blood and peritoneal cavity [69]. The generally accepted scheme for endotoxin binding is to CD14-bearing receptor cells (monocytes, macrophages, dendritic cells, and possibly vascular endothelial cells), which then associates with the TLR4-MD-2 complex to initiate a downstream signal, causing a proinflammatory response, such as leukocyte recruitment [53]. Macrophage-derived cytokines (such as IL-1b and TNF), as well as arachidonic acid metabolites (i.e., prostacyclin and thromboxane), are responsible for many of the pathophysiologic consequences of endotoxemia and tissue injury in equine colic cases. Endotoxins among other things activate inducible nitric oxide synthase (iNOS) in intestinal macrophages [66]. The resultant increase in NO release stimulates decreased smooth muscle contractility. In healthy ponies, IV infusion of endotoxin also resulted in inhibition of motility in the stomach, cecum, left dorsal colon, and small colon [70]. However, no nasogastric reflux was observed. Although motility in the small intestine was increased, its myoelectric pattern was abnormal. The effects of endotoxins on motility were partially mediated by PGE2 possibly stimulating alpha-2 adrenergic receptors [28, 51, 71]. A platelet-activating factor (PAF) antagonist suppressed some of the endotoxin-induced inhibition of motility in horses. These findings led to the conclusion that the PAF may also play a role in the development of POI [68]. The degree of endotoxic shock in horses is directly dependent on the forms and time span of gastrointestinal disease [72]. As the concentration of Gram-negative bacteria is highest in the large intestine of horses, the release of endotoxin and development of endotoxic shock are logically expected in pathologies of this part of the gastrointestinal tract, for instance by volvulus or colitis [43]. In the small intestine of horses, different population of Gram-negative bacteria exist, but in lower concentrations than observed in the large intestine. It would therefore be expected that in this case the endotoxins would not play a decisive role in development of POI. In contrast to this theory in one study of colic cases, the highest endotoxin concentrations were found in horses with entrapment in the foramen omentalis,

**144**

Activation of CRF receptors in the hypothalamus of horses mediates almost the entire repertoire of behavioral, neuroendocrine, autonomic, immunologic and visceral responses characteristic of stress syndrome [77, 90]. CRF release is the first step in activation of the hypothalamic-pituitary-adrenal axis (HPA axis) involved in stress response. The magnitude and duration of the activation in the HPA axis are proportional to the initial tissue damage and surgical injury, but also in other perioperative stress conditions. The pituitary gland responds to CRF by synthesizing a larger precursor molecule, proopiomelanocortin, which is metabolized within the pituitary into ACTH, β-endorphin and N-terminal precursor. Growth hormones and prolactin are also secreted in increased amounts from the pituitary in response to a surgical stimulus. Surgery is one of the most potent activators of ACTH and cortisol secretion; therefore, increased plasma concentrations of both hormones in human can be measured within minutes of the start of surgery [91]. Usually, a feedback mechanism operates so that increased concentrations of circulating cortisol inhibit further secretion of ACTH. This control mechanism appears to be ineffective after surgery resulting in elevated concentrations of both hormones [80]. Cortisol has known complex metabolic effects on the metabolism of carbohydrate, fat and protein. Cortisol impairs inflammation, which is helpful in the short term during conditions such as 'fight-or-flight,' also referred to as hyperarousal, or the acute stress response. In response to surgical trauma, massive levels of catecholamine (adrenaline, noradrenaline and dopamine) and glucagons are also released, while serum insulin concentrations decrease relatively [91]. The overall metabolic effect of the hormonal changes is increased catabolism, which mobilizes substrates to provide energy sources, and a mechanism to retain salt and water and maintain fluid volume and cardiovascular homeostasis [86]. According to our own preliminary research results (unpublished data), the cortisol levels increased from a baseline in the postoperative days after colic surgery, but more remarkably in POI group horses.

It seems that upon inflammation, there are numerous neurotransmitters that are mediated through surgical and postoperative stress, which caused disturbances in the motility of the gastrointestinal tract [92]. In an experimental model in ponies, using jejunal trauma through sympathetic reflexes and inflammation, electrical activity was decreased and the normal synchrony of gastric and duodenal MMCs was disrupted [8]. Intestinal manipulation of the small intestine in rodents impairs intestinal transit, through an inhibitory adrenergic pathway, because its sympathetic blockade is not always successful in reversing the inhibition of gastrointestinal motility induced by abdominal surgical procedures [93, 94]. In addition to sympathetic reflexes, surgical manipulation of the intestines activates inhibitory non-adrenergic, non-cholinergic (NANC) neurons in the gastrointestinal tract, resulting in the release primarily of NO and VIP, the consequences of which result in decreased gastrointestinal motility [93, 95, 96]. Substance P, which is a neurotransmitter involved in pain, has also been hypothesized to have a role in postoperative ileus [85]. In a model of POI in rats, where mechanical trauma to the small intestine and cecum was used, reserpine (which depletes catecholamine stores) and L-nitroarginine (a nitric-oxide synthase inhibitor) completely reversed the inhibition of ingesta transit. This finding supported the involvement of adrenergic and nitrergic neurons in the pathogenesis of POI [93]. As blockade of the calcitoningene-related peptide resulted in a similar effect, this peptide may be one of the neurotransmitters released by these afferent fibers and partly mediate postoperative ileus [97]. Additionally, endogenous opioids are also released after surgery and contribute toward postoperative ileus [92].

Other changes also occur following surgery stress, notably an increase in cytokine production. In human patients after surgery, cytokines IL-1, TNF-α and IL-6 may augment pituitary ACTH secretion and subsequently increase the release of cortisol.

**147**

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal…*

Most studies concentrate on central mechanisms whereby a stressful event perceived by the brain triggers neuronal and hormonal reflexes that influence the gastrointestinal motility. According to one study, the intestine produces the same stress peptides that are present in the central nervous system [99]. A local stressor, in this case endotoxins, results in the local generation and action of stress peptides that mediate inflammation without involving the central nervous system. In other words, the peripheral stressors induce local release of CRF possibly from enteric neurons and immune cells [88]. Peripherally derived CRF may act on the enteric nervous system and mast cells to induce inflammation and control motility and

The pharmacological mechanisms of postoperative ileus are well described in the literature. Xylazine and detomidine are α2-adrenergic agonists and are commonly used in horses for sedation and pain control. Activation of presynaptic α2-adrenergic receptors within the enteric nervous system inhibits ACh release from cholinergic neurons, thereby suppressing intestinal contractions in normal ponies, primarily of the distal jejunum, pelvic flexure, cecum, and right ventral colon [100–102]. Although the use of α2-agonists has been reported to suppress intestinal motility, no direct significant associations have been made between POI

Anesthesia gases do have an effect on intestinal motility, and the longer anesthesia lasts, the greater the actions [85]. Based on our observations during 1997–2000, the incidence of POI was greater than after the year 2000. One of the reasons for this was that the active use of halothane was stopped, and we began to use isoflurane as an anesthetic gas. Other studies have also shown that anesthetic drugs such as halothane and atropine tend to decrease gastric emptying and inhibit intestinal motility, with the greatest effect on the colon and cecum and they can initiate cecal impaction in horses [103–105]. Interestingly, the cecal impaction occurs more commonly after orthopedic procedures [106]. Therefore, general anesthesia herein appears to be a less likely primary cause of cecal and small intestine motility dysfunction [104, 107]. Possibly, persistent pain after orthopedic procedures, resulting

Large intestinal dysmotility is commonly recognized following a delay in defecation and also by rectal and/or ultrasonographic examination. There are different criteria for the diagnosis of equine small intestine POI in the literature [15–17, 108, 109]. Based on our previous experience and regardless of the rare cases of exclusion, the main criteria

1.Postoperative period during 1–7 days after abdominal surgery. Most cases of

2.Postoperative reflux of ≥2 l upon any given intubation, or > 2 l/h on repeated intubation, of gastric contents with pH ≥ 6.0. Another study defined cases of postoperative ileus as horses with >20 l during a 24-h period, or >8 l during any single refluxing event [110]. Merrit and Blikslager [111] suggested the adoption

in sympathetic overstimulation, is a significant contributing factor.

POI occur within 12–48 h after recovery from anesthesia.

**5. Diagnosis of equine postoperative ileus**

for diagnosis of POI of small intestine are as follows:

A negative feedback system partially exists; therefore, glucocorticoids inhibit

*DOI: http://dx.doi.org/10.5772/intechopen.91290*

cytokine production and inflammation [98].

**4.3 The role of drugs and anesthetic agents**

and sedation or type of sedative used.

secretion [89].

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal… DOI: http://dx.doi.org/10.5772/intechopen.91290*

A negative feedback system partially exists; therefore, glucocorticoids inhibit cytokine production and inflammation [98].

Most studies concentrate on central mechanisms whereby a stressful event perceived by the brain triggers neuronal and hormonal reflexes that influence the gastrointestinal motility. According to one study, the intestine produces the same stress peptides that are present in the central nervous system [99]. A local stressor, in this case endotoxins, results in the local generation and action of stress peptides that mediate inflammation without involving the central nervous system. In other words, the peripheral stressors induce local release of CRF possibly from enteric neurons and immune cells [88]. Peripherally derived CRF may act on the enteric nervous system and mast cells to induce inflammation and control motility and secretion [89].

#### **4.3 The role of drugs and anesthetic agents**

*Equine Science*

Activation of CRF receptors in the hypothalamus of horses mediates almost the entire repertoire of behavioral, neuroendocrine, autonomic, immunologic and visceral responses characteristic of stress syndrome [77, 90]. CRF release is the first step in activation of the hypothalamic-pituitary-adrenal axis (HPA axis) involved in stress response. The magnitude and duration of the activation in the HPA axis are proportional to the initial tissue damage and surgical injury, but also in other perioperative stress conditions. The pituitary gland responds to CRF by synthesizing a larger precursor molecule, proopiomelanocortin, which is metabolized within the pituitary into ACTH, β-endorphin and N-terminal precursor. Growth hormones and prolactin are also secreted in increased amounts from the pituitary in response to a surgical stimulus. Surgery is one of the most potent activators of ACTH and cortisol secretion; therefore, increased plasma concentrations of both hormones in human can be measured within minutes of the start of surgery [91]. Usually, a feedback mechanism operates so that increased concentrations of circulating cortisol inhibit further secretion of ACTH. This control mechanism appears to be ineffective after surgery resulting in elevated concentrations of both hormones [80]. Cortisol has known complex metabolic effects on the metabolism of carbohydrate, fat and protein. Cortisol impairs inflammation, which is helpful in the short term during conditions such as 'fight-or-flight,' also referred to as hyperarousal, or the acute stress response. In response to surgical trauma, massive levels of catecholamine (adrenaline, noradrenaline and dopamine) and glucagons are also released, while serum insulin concentrations decrease relatively [91]. The overall metabolic effect of the hormonal changes is increased catabolism, which mobilizes substrates to provide energy sources, and a mechanism to retain salt and water and maintain fluid volume and cardiovascular homeostasis [86]. According to our own preliminary research results (unpublished data), the cortisol levels increased from a baseline in the postoperative days after colic surgery, but more remarkably in POI group horses.

It seems that upon inflammation, there are numerous neurotransmitters that are mediated through surgical and postoperative stress, which caused disturbances in the motility of the gastrointestinal tract [92]. In an experimental model in ponies, using jejunal trauma through sympathetic reflexes and inflammation, electrical activity was decreased and the normal synchrony of gastric and duodenal MMCs was disrupted [8]. Intestinal manipulation of the small intestine in rodents impairs intestinal transit, through an inhibitory adrenergic pathway, because its sympathetic blockade is not always successful in reversing the inhibition of gastrointestinal motility induced by abdominal surgical procedures [93, 94]. In addition to sympathetic reflexes, surgical manipulation of the intestines activates inhibitory non-adrenergic, non-cholinergic (NANC) neurons in the gastrointestinal tract, resulting in the release primarily of NO and VIP, the consequences of which result in decreased gastrointestinal motility [93, 95, 96]. Substance P, which is a neurotransmitter involved in pain, has also been hypothesized to have a role in postoperative ileus [85]. In a model of POI in rats, where mechanical trauma to the small intestine and cecum was used, reserpine (which depletes catecholamine stores) and L-nitroarginine (a nitric-oxide synthase inhibitor) completely reversed the inhibition of ingesta transit. This finding supported the involvement of adrenergic and nitrergic neurons in the pathogenesis of POI [93]. As blockade of the calcitoningene-related peptide resulted in a similar effect, this peptide may be one of the neurotransmitters released by these afferent fibers and partly mediate postoperative ileus [97]. Additionally, endogenous opioids are also released after surgery and

Other changes also occur following surgery stress, notably an increase in cytokine production. In human patients after surgery, cytokines IL-1, TNF-α and IL-6 may augment pituitary ACTH secretion and subsequently increase the release of cortisol.

**146**

contribute toward postoperative ileus [92].

The pharmacological mechanisms of postoperative ileus are well described in the literature. Xylazine and detomidine are α2-adrenergic agonists and are commonly used in horses for sedation and pain control. Activation of presynaptic α2-adrenergic receptors within the enteric nervous system inhibits ACh release from cholinergic neurons, thereby suppressing intestinal contractions in normal ponies, primarily of the distal jejunum, pelvic flexure, cecum, and right ventral colon [100–102]. Although the use of α2-agonists has been reported to suppress intestinal motility, no direct significant associations have been made between POI and sedation or type of sedative used.

Anesthesia gases do have an effect on intestinal motility, and the longer anesthesia lasts, the greater the actions [85]. Based on our observations during 1997–2000, the incidence of POI was greater than after the year 2000. One of the reasons for this was that the active use of halothane was stopped, and we began to use isoflurane as an anesthetic gas. Other studies have also shown that anesthetic drugs such as halothane and atropine tend to decrease gastric emptying and inhibit intestinal motility, with the greatest effect on the colon and cecum and they can initiate cecal impaction in horses [103–105]. Interestingly, the cecal impaction occurs more commonly after orthopedic procedures [106]. Therefore, general anesthesia herein appears to be a less likely primary cause of cecal and small intestine motility dysfunction [104, 107]. Possibly, persistent pain after orthopedic procedures, resulting in sympathetic overstimulation, is a significant contributing factor.

#### **5. Diagnosis of equine postoperative ileus**

Large intestinal dysmotility is commonly recognized following a delay in defecation and also by rectal and/or ultrasonographic examination. There are different criteria for the diagnosis of equine small intestine POI in the literature [15–17, 108, 109]. Based on our previous experience and regardless of the rare cases of exclusion, the main criteria for diagnosis of POI of small intestine are as follows:


#### **Figure 2.**

*(A) Transcutaneous ultrasonogram in a horse with POI before surgery in region 3 l with evidence of multiple fluid-distended small intestinal bowel loops [113]. (B) Jejunojejunal distension identified during repeat celiotomy in the same horse.*

of a consensus on the classification of clinical criteria for POI, which included ≥4 l on any given intubation or > 2 l/h on repeated intubation. In most of our cases of POI, an average of 8–12 l, if intubation is performed every 4–5 h (i.e., approximately 2 l/h of fluid accumulate in the stomach). If more reflux is noticed, other pathologies are possible (e.g., mechanical obstructions and anastomotic leaks).


#### **6. Prevention and treatment of equine postoperative ileus**

Since the treatment of this condition is very complex, and the complications are often fatal, the prevention strategy of POI is a very important way to improve the survival rate of horses that have undergone abdominal surgery [34, 109]. There are many methods and procedures and prophylactic and therapeutic choices for equine POI, depending on each individual case. The preventive strategies come from better

**149**

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal…*

understanding the pathogenesis of this condition and treatment of POI must first address the underlying cause(s). The prophylactic and treatment strategies of the equine POI we are currently proposing are a multimodal regimen, which can be divided into three phases pre-, intra- and postoperative. The proposed multimodal treatment approach should include limiting factors, which are known to contribute to postoperative ileus. Each phase has the same significance in survival rate of

The long onset of colic disease producing high degree of endotoxic shock, in accordance with our earlier findings [32], are strongly associated with an increased risk for POI development. In this regard, it is appropriate to again highlight the importance of timely referral and prompt surgical intervention in surgical (strangulation) colic cases for the prevention of POI. Additionally, time from onset of colic to surgery has a decisive role not only in prophylactic but also in terms of a successful treatment by occurrence of equine POI. Failure to refer promptly leads to not only POI but also the occurrence of other perioperative complications by abdominal surgery in the horse. Approximately, every hour of tardiness with surgical interventions in a horse with strangulation ileus (for instance, by small intestine or large colon volvulus) reduces the survival rate from 5 to 10%, due to the rapid development of endotoxic shock [4, 116]. We found a significant correlation between the occurrence and survival of POI with colic duration in horses with inguinal hernia (*r* = 0.72) and epiploic foramen entrapment (*r* = 0.78), and partially (not significant) due to ileum obstipation (*r* = 0.41) [40, 41, 45]. According to our recent study in 33 horses with entrapment in the epiploic foramen, surgery performed within 6 h from onset of colic had a survival rate of 87%, compared with

It is important even before the onset of surgery to prepare, applying medicaments

that reduce endotoxin release and alleviate inflammation effect, for instance, the application of NSAIDs (flunixin meglumine), corticosteroids (prednisolone) and antibiotics. Administration of corticosteroid drugs to critically ill surgical colic horses results in a significant reduction of shock symptoms. The use of these drugs should certainly continue in the postoperative period [26]. Antimicrobials should be administered intravenously, ideally within 30–60 min before the first surgical incision. For horses undergoing abdominal surgery in the perioperative period, we introduced the following antibiotics: cobactan® 2.5% (cefquinome) (IM 3 mg/kg BW) for 5 d; gentamicin (6.6 mg/kg BW, IV, q24h) and metronidazole (20 mg/kg BW IV, four times daily) for 3 days. Additionally, if time permits, during urgent transport to the equine clinic, horses should have a balanced polyionic intravenous fluid applied in order to reduce hemoconcentration. It is advisable that before abdominal surgery horses should have a hematocrit level of below 0.45 l/l. In cases of metabolic acidosis, 5% sodium bicarbonate solution should also be administered. We used pre- and intraoperative the hypertonic saline (NaCl 8.0%) only in horses with severe endotoxic shock

**6.1 Preoperative strategies in the prevention of equine POI**

25% survival with surgery 10 h or more after onset [40].

and if in doubt on the presence of intestinal edema [40].

**6.2 Intraoperative strategies in the prevention of equine POI**

Surgical procedures and anesthesia affect the development of POI in horses (as discussed above). Operative management should be aimed at reducing duration of surgery and anesthesia in addition to other preventative strategies. In this aspect, an important role is played by a high-performing multidisciplinary surgical team with experience and knowledge as this optimizes surgical procedures. During the

*DOI: http://dx.doi.org/10.5772/intechopen.91290*

equine POI.

understanding the pathogenesis of this condition and treatment of POI must first address the underlying cause(s). The prophylactic and treatment strategies of the equine POI we are currently proposing are a multimodal regimen, which can be divided into three phases pre-, intra- and postoperative. The proposed multimodal treatment approach should include limiting factors, which are known to contribute to postoperative ileus. Each phase has the same significance in survival rate of equine POI.

#### **6.1 Preoperative strategies in the prevention of equine POI**

The long onset of colic disease producing high degree of endotoxic shock, in accordance with our earlier findings [32], are strongly associated with an increased risk for POI development. In this regard, it is appropriate to again highlight the importance of timely referral and prompt surgical intervention in surgical (strangulation) colic cases for the prevention of POI. Additionally, time from onset of colic to surgery has a decisive role not only in prophylactic but also in terms of a successful treatment by occurrence of equine POI. Failure to refer promptly leads to not only POI but also the occurrence of other perioperative complications by abdominal surgery in the horse. Approximately, every hour of tardiness with surgical interventions in a horse with strangulation ileus (for instance, by small intestine or large colon volvulus) reduces the survival rate from 5 to 10%, due to the rapid development of endotoxic shock [4, 116]. We found a significant correlation between the occurrence and survival of POI with colic duration in horses with inguinal hernia (*r* = 0.72) and epiploic foramen entrapment (*r* = 0.78), and partially (not significant) due to ileum obstipation (*r* = 0.41) [40, 41, 45]. According to our recent study in 33 horses with entrapment in the epiploic foramen, surgery performed within 6 h from onset of colic had a survival rate of 87%, compared with 25% survival with surgery 10 h or more after onset [40].

It is important even before the onset of surgery to prepare, applying medicaments that reduce endotoxin release and alleviate inflammation effect, for instance, the application of NSAIDs (flunixin meglumine), corticosteroids (prednisolone) and antibiotics. Administration of corticosteroid drugs to critically ill surgical colic horses results in a significant reduction of shock symptoms. The use of these drugs should certainly continue in the postoperative period [26]. Antimicrobials should be administered intravenously, ideally within 30–60 min before the first surgical incision. For horses undergoing abdominal surgery in the perioperative period, we introduced the following antibiotics: cobactan® 2.5% (cefquinome) (IM 3 mg/kg BW) for 5 d; gentamicin (6.6 mg/kg BW, IV, q24h) and metronidazole (20 mg/kg BW IV, four times daily) for 3 days. Additionally, if time permits, during urgent transport to the equine clinic, horses should have a balanced polyionic intravenous fluid applied in order to reduce hemoconcentration. It is advisable that before abdominal surgery horses should have a hematocrit level of below 0.45 l/l. In cases of metabolic acidosis, 5% sodium bicarbonate solution should also be administered. We used pre- and intraoperative the hypertonic saline (NaCl 8.0%) only in horses with severe endotoxic shock and if in doubt on the presence of intestinal edema [40].

#### **6.2 Intraoperative strategies in the prevention of equine POI**

Surgical procedures and anesthesia affect the development of POI in horses (as discussed above). Operative management should be aimed at reducing duration of surgery and anesthesia in addition to other preventative strategies. In this aspect, an important role is played by a high-performing multidisciplinary surgical team with experience and knowledge as this optimizes surgical procedures. During the

*Equine Science*

**Figure 2.**

*celiotomy in the same horse.*

anastomotic leaks).

examination.

abdomen (**Figure 2**) [112–114].

dorsally behind the right costal arch [48, 115].

**6. Prevention and treatment of equine postoperative ileus**

of a consensus on the classification of clinical criteria for POI, which included ≥4 l on any given intubation or > 2 l/h on repeated intubation. In most of our cases of POI, an average of 8–12 l, if intubation is performed every 4–5 h (i.e., approximately 2 l/h of fluid accumulate in the stomach). If more reflux is noticed, other pathologies are possible (e.g., mechanical obstructions and

*(A) Transcutaneous ultrasonogram in a horse with POI before surgery in region 3 l with evidence of multiple fluid-distended small intestinal bowel loops [113]. (B) Jejunojejunal distension identified during repeat* 

3.Moderate abdominal discomfort, which intensifies every 4–5 h after the last intubation. The response to nasogastric decompression provides an important clue that the problem is functional (i.e., POI). If a high degree of pain is no-

ticed and continues, other gastrointestinal pathologies are possible.

6.Evidence of multiple fluid-distended small intestinal loops on rectal

4.Heart frequency 40–65 beats/min, if intubation is performed every 4–5 h.

5.Hematocrit 0.40–0.50 l/l, if standard infusion therapy is performed. If a high hematocrit is noticed, other gastrointestinal pathologies are possible.

7.Ultrasonographic evidence of multiple fluid-distended small intestinal bowel loops (≥3 cm), edema and lack of motility in different parts of the equine

8.Borborygmi are usually decreased, especially the absence the ileocecal noise

Since the treatment of this condition is very complex, and the complications are often fatal, the prevention strategy of POI is a very important way to improve the survival rate of horses that have undergone abdominal surgery [34, 109]. There are many methods and procedures and prophylactic and therapeutic choices for equine POI, depending on each individual case. The preventive strategies come from better

**148**

abdominal surgery, the least traumatic surgical methods should be selected and performed and these should be carried out as efficiently and therefore quickly as possible. The degree of inhibition of circular muscle contractility is related directly to the magnitude of leukocyte and macrophage infiltration, which in turn depends on the intensity of intestinal manipulation; therefore, every effort should be made to reduce intestinal trauma. One surgical method able to reduce surgery time is the use of the stapled technique for jejunal resections [117]. As already described above, other postoperative complications in horses undergoing abdominal surgeries have an impact in developing POI, notably by postanesthetic myopathy [118, 119]. Therefore, special attention must be paid to optimizing blood pressure during abdominal surgery. For these purposes, anesthesia monitoring should be carried out at all the time, and if a decrease in blood pressure (defined as mean arterial pressure <70 mmHg) is observed, a dobutamine injection should be administered [42, 46]. In cases of severe anesthetic hypoxia (PO2 < 70 mmHg), one ought to have the issue resolved in a timely manner with intermittent positive pressure ventilation (IPPV) with constant positive end-expiratory pressure.

Several methods have recently been developed to decrease the rate of other surgical complications [35, 117]. The methods of minimizing postoperative adhesions are the application of meticulous atraumatic surgical technique, use of a bioresorbable hyaluronate-carboxymethylcellulose membrane [118, 120], administration of heparin [40], omentectomy [121] and performing intraoperative peritoneal lavage [39]. In the case of strangulating obstruction of the small intestine, the bowel to be resected and discarded should be placed over the edge of the surgical field while removing the contents of the small intestine. Performing a pelvic flexure enterotomy may also reduce POI risk [110], which has also been confirmed during our observations [45]. The protective influence of these procedures may be attributable to a reduction in the intraluminal source of endotoxin, but the potential value of evacuating the colon should be weighed against the increased anesthesia time required to perform the surgery, as both factors have been associated with an increased risk of POI [106].

#### **6.3 Postoperative strategies in the prevention and therapy of equine POI**

Postoperative strategies in the prevention and treatment of equine POI are numerous and dependent on each individual case [26]. This can be divided into standard supportive postoperative procedures and procedure by risk for the patient. Under standard management, the following should be considered: regular basic clinical measurements (every 4–5 h) including heart and respiration frequency, temperature, auscultation of bowel sound, and of laboratory parameters including hematocrit, total plasma protein and acid-base state of the blood. In the standard postoperative procedures, several checks should be undertaken. We used at least 3 days administration of balanced polyionic intravenous fluid. The amount and length of time of the infusion solution are dependent on blood parameters; on average, we applied 2.5–3 l/h/500 kg BW. Dehydration and electrolyte imbalances are commonly encountered as a result of abdominal disorders and surgery. Even though a horse is stabilized in the perioperative period and the primary problem is corrected, continued replacement of previous and ongoing fluid losses is critical for a successful outcome. If a horse has gastric reflux, the use of the infusion solution should be continued throughout this condition. Given that the introduction of a large number of solutions provokes the development of thrombophlebitis of the jugular veins, it is recommended that a central catheter is installed through the abdominal vein.

In all horses without and with POI after abdominal surgery, NSAIDs should be administered such as flunixin meglumine (1.1 mg/kg BW, IV, q12h initially for

**151**

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal…*

Postoperative peritoneal lavage has been used in an attempt to reduce the rate of postoperative adhesions [119], but this procedure decreases occurrence and increases survival rates of equine POI [39]. Thus, in horses with a high risk of POI and who additionally showed symptoms of peritonitis, we performed retrograde peritoneal lavage through a Foley catheter, which was installed into the abdominal cavity prior to closure of the abdominal incision. For abdomen lavage, we used sterile physiologic saline or Ringer's lactate solution (10–15 l) containing amoxicillin

The use of prokinetics in horses with POI is only part of the treatment and is not defined as a unique technique toward the survival rate of this disease, only working in combination with other methods [5]. The effectiveness of some prokinetic drugs in horses is associated with the difficulties of conducting a well-designed, randomized clinical trial with homogenous groups of animals [38]. None of the intestinal prokinetic agents have been subject to rigorous clinical efficacy trials [122]. This statement is supported by the fact that the contractile response of intestinal smooth muscle to prokinetic drugs is significantly impaired in many horses with POI. Prokinetic motility drugs are also commonly used following abdominal surgery in humans to prevent ileus, although a Cochrane review examined 39 randomized controlled trials and found most medications to be of little or no benefit [6, 7]. There are numerous prokinetics drugs that can be used by POI in the horse, which

**6.5 Prokinetic drugs for the treatment of equine postoperative ileus**

have differing mechanisms of action and different efficiency rates [26].

Parasympathomimetic agents (cholinomimetics) are drugs that mimic the effects of the parasympathetic nervous system activity. Directly acting parasympathomimetic agents, bethanechol chloride, improve myoelectric activity in the stomach, jejunum, ileum, and large and small colons of horses, but produce significant cholinergic side effects (increased salivation), and therefore are not used as a standard in equine praxis [71, 101]. In horses with POI, applications are mostly indirectly acting parasympathomimetic agents such as neostigmine methylsulfate. Neostigmine is a cholinesterase inhibitor that prolongs the activity of acetylcholine by retarding its breakdown at the synaptic junction [102, 123]. Neostigmine has been shown to delay gastric emptying and decrease jejunal myoelectric activity, but enhances myoelectric activity in the ileum, cecum, right ventral colon and

*6.5.1 Parasympathomimetic agents (cholinomimetics)*

2 days, then 0.55 mg/kg BW, IV, q12h for at least 2 days). Flunixin meglumine controls postoperative pain and improves the cardiovascular manifestations of endotoxemia. Additionally, flunixin meglumine has been shown to significantly attenuate the disruption of gastric, small intestine, and large colon motility elicited by endotoxin infusion [49]. Additional treatments include anti-oxidant medications, which prevent the generation of chemoattractants: DMSO (20 mg/kg BW in 1 l saline IV bolus, q12h) and sodium heparin (20,000 IU, SQ, q12h). In all postoperative horses without gastric reflux, we applied obligatory laxatives (2 l liquid paraffin, p.o.) after abdominal surgery. For the prevention of incisional infection, horses received abdominal bandages during hospitalization. The bandages consisted of sterile absorbent cotton padding next to the incision secured by elastic

*DOI: http://dx.doi.org/10.5772/intechopen.91290*

**6.4 Postoperative peritoneal lavage**

(5 g) and 20,000 units of sodium heparin.

adhesive tape.

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal… DOI: http://dx.doi.org/10.5772/intechopen.91290*

2 days, then 0.55 mg/kg BW, IV, q12h for at least 2 days). Flunixin meglumine controls postoperative pain and improves the cardiovascular manifestations of endotoxemia. Additionally, flunixin meglumine has been shown to significantly attenuate the disruption of gastric, small intestine, and large colon motility elicited by endotoxin infusion [49]. Additional treatments include anti-oxidant medications, which prevent the generation of chemoattractants: DMSO (20 mg/kg BW in 1 l saline IV bolus, q12h) and sodium heparin (20,000 IU, SQ, q12h). In all postoperative horses without gastric reflux, we applied obligatory laxatives (2 l liquid paraffin, p.o.) after abdominal surgery. For the prevention of incisional infection, horses received abdominal bandages during hospitalization. The bandages consisted of sterile absorbent cotton padding next to the incision secured by elastic adhesive tape.

#### **6.4 Postoperative peritoneal lavage**

*Equine Science*

positive end-expiratory pressure.

increased risk of POI [106].

abdominal surgery, the least traumatic surgical methods should be selected and performed and these should be carried out as efficiently and therefore quickly as possible. The degree of inhibition of circular muscle contractility is related directly to the magnitude of leukocyte and macrophage infiltration, which in turn depends on the intensity of intestinal manipulation; therefore, every effort should be made to reduce intestinal trauma. One surgical method able to reduce surgery time is the use of the stapled technique for jejunal resections [117]. As already described above, other postoperative complications in horses undergoing abdominal surgeries have an impact in developing POI, notably by postanesthetic myopathy [118, 119]. Therefore, special attention must be paid to optimizing blood pressure during abdominal surgery. For these purposes, anesthesia monitoring should be carried out at all the time, and if a decrease in blood pressure (defined as mean arterial pressure <70 mmHg) is observed, a dobutamine injection should be administered [42, 46]. In cases of severe anesthetic hypoxia (PO2 < 70 mmHg), one ought to have the issue resolved in a timely manner with intermittent positive pressure ventilation (IPPV) with constant

Several methods have recently been developed to decrease the rate of other surgical complications [35, 117]. The methods of minimizing postoperative adhesions are the application of meticulous atraumatic surgical technique, use of a bioresorbable hyaluronate-carboxymethylcellulose membrane [118, 120], administration of heparin [40], omentectomy [121] and performing intraoperative peritoneal lavage [39]. In the case of strangulating obstruction of the small intestine, the bowel to be resected and discarded should be placed over the edge of the surgical field while removing the contents of the small intestine. Performing a pelvic flexure enterotomy may also reduce POI risk [110], which has also been confirmed during our observations [45]. The protective influence of these procedures may be attributable to a reduction in the intraluminal source of endotoxin, but the potential value of evacuating the colon should be weighed against the increased anesthesia time required to perform the surgery, as both factors have been associated with an

**6.3 Postoperative strategies in the prevention and therapy of equine POI**

Postoperative strategies in the prevention and treatment of equine POI are numerous and dependent on each individual case [26]. This can be divided into standard supportive postoperative procedures and procedure by risk for the patient. Under standard management, the following should be considered: regular basic clinical measurements (every 4–5 h) including heart and respiration frequency, temperature, auscultation of bowel sound, and of laboratory parameters including hematocrit, total plasma protein and acid-base state of the blood. In the standard postoperative procedures, several checks should be undertaken. We used at least 3 days administration of balanced polyionic intravenous fluid. The amount and length of time of the infusion solution are dependent on blood parameters; on average, we applied 2.5–3 l/h/500 kg BW. Dehydration and electrolyte imbalances are commonly encountered as a result of abdominal disorders and surgery. Even though a horse is stabilized in the perioperative period and the primary problem is corrected, continued replacement of previous and ongoing fluid losses is critical for a successful outcome. If a horse has gastric reflux, the use of the infusion solution should be continued throughout this condition. Given that the introduction of a large number of solutions provokes the development of thrombophlebitis of the jugular veins, it is recommended that a central catheter is installed through the abdominal vein. In all horses without and with POI after abdominal surgery, NSAIDs should be administered such as flunixin meglumine (1.1 mg/kg BW, IV, q12h initially for

**150**

Postoperative peritoneal lavage has been used in an attempt to reduce the rate of postoperative adhesions [119], but this procedure decreases occurrence and increases survival rates of equine POI [39]. Thus, in horses with a high risk of POI and who additionally showed symptoms of peritonitis, we performed retrograde peritoneal lavage through a Foley catheter, which was installed into the abdominal cavity prior to closure of the abdominal incision. For abdomen lavage, we used sterile physiologic saline or Ringer's lactate solution (10–15 l) containing amoxicillin (5 g) and 20,000 units of sodium heparin.

#### **6.5 Prokinetic drugs for the treatment of equine postoperative ileus**

The use of prokinetics in horses with POI is only part of the treatment and is not defined as a unique technique toward the survival rate of this disease, only working in combination with other methods [5]. The effectiveness of some prokinetic drugs in horses is associated with the difficulties of conducting a well-designed, randomized clinical trial with homogenous groups of animals [38]. None of the intestinal prokinetic agents have been subject to rigorous clinical efficacy trials [122]. This statement is supported by the fact that the contractile response of intestinal smooth muscle to prokinetic drugs is significantly impaired in many horses with POI. Prokinetic motility drugs are also commonly used following abdominal surgery in humans to prevent ileus, although a Cochrane review examined 39 randomized controlled trials and found most medications to be of little or no benefit [6, 7]. There are numerous prokinetics drugs that can be used by POI in the horse, which have differing mechanisms of action and different efficiency rates [26].

#### *6.5.1 Parasympathomimetic agents (cholinomimetics)*

Parasympathomimetic agents (cholinomimetics) are drugs that mimic the effects of the parasympathetic nervous system activity. Directly acting parasympathomimetic agents, bethanechol chloride, improve myoelectric activity in the stomach, jejunum, ileum, and large and small colons of horses, but produce significant cholinergic side effects (increased salivation), and therefore are not used as a standard in equine praxis [71, 101]. In horses with POI, applications are mostly indirectly acting parasympathomimetic agents such as neostigmine methylsulfate. Neostigmine is a cholinesterase inhibitor that prolongs the activity of acetylcholine by retarding its breakdown at the synaptic junction [102, 123]. Neostigmine has been shown to delay gastric emptying and decrease jejunal myoelectric activity, but enhances myoelectric activity in the ileum, cecum, right ventral colon and

pelvic flexure activity in healthy ponies [71, 122]. These results suggest that the drug would not be appropriate for gastric and small intestinal problems but may be beneficial for large intestinal motility dysfunction. However, neostigmine increased the amplitude of rhythmic contractions in both the resting and distended jejunum in anesthetized ponies, and it induced contractile activity in the ileum, supporting its use for motility dysfunction in both the small and large intestine [26, 29, 124]. Based on our clinical impressions, neostigmine if used as monotherapy repeated at 60 min intervals (during 24–48 h) has significant beneficial effects in the treatment of colitis cases, but not in POI of the small intestine [43].

#### *6.5.2 Sodium channel blockers*

Sodium channel blockers—lidocaine is currently a prokinetic agent, which is most frequently used for the treatment of POI in equine practice, although scientific evidence on its prokinetic and analgesic effectiveness is limited [33, 124–128]. Lidocaine has antinociceptive, antihyperalgesic, and anti-inflammatory effects [6, 7]. In an investigation within a UK hospital population, lidocaine therapy had no effect on the prevalence of postoperative reflux, total reflux volume or duration of reflux and as well as no effect on postoperative survival in horses undergoing abdominal surgery [129]. According to our observations, lidocaine if used as monotherapy has little positive effect on the treatment of equine POI and is significantly inferior to a combination of prokinetic drugs [32].

#### *6.5.3 Drugs acting as 5-hydroxytryptamine receptors*

Drugs acting as 5-hydroxytryptamine receptors include metoclopramide, cisapride, mosapride citrate and tegaserod [36, 130–132]. Metoclopramide hydrochloride (MCP) is a first-generation substituted benzamide whose prokinetic activity is both through dopamine 1 (DA1) and 2 (DA2) receptor antagonism and through 5-HT 4-receptor (5-HT4) agonism and 5-HT3 receptor antagonism [11]. Stimulation of DA2 receptors inhibits the release of acetylcholine, and stimulation of 5-HT4 receptors enhances the release of acetylcholine from the myenteric ganglia. MCP is a drug, which for a long time has often been used in the prevention and treatment of equine POI, but results in published studies have been variable [5, 8, 21, 130]. The prokinetic capacity of metoclopramide appears substantial in the equine stomach, duodenum and jejunum, but not in the large intestine [128, 133].

#### *6.5.4 Motilin agonists*

Motilin agonists include erythromycin lactobionate, and a macrolide antibiotic has been shown to significantly increase solid phase gastric and dose-dependent cacal emptying and is thought to exert prokinetic effects via activation of motilin receptors [20, 21, 36]. The prokinetic effects of erythromycin reported in healthy horses were not the same in horses with gastrointestinal disease [110, 122, 128].

#### *6.5.5 Adrenergic antagonists*

Adrenergic antagonists include acepromazine maleate, a nonselective α-adrenergic antagonist, and yohimbine, tolazamide, and atipamezole, which are selective α2-adrenergic antagonists. Their use as prokinetics is based on the assumption that sympathetic hyperactivity contributes to POI, but their beneficial effects are not well understood [6, 7].

**153**

surgery).

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal…*

Dopamine antagonist—domperidone is a selective peripheral DA2 receptor antagonist [26]. In a preliminary experimental model of POI in ponies, domperidone was effective in restoring transit time, electromechanical activity, and coordi-

Combination of prokinetic drugs—based on our research, the best medicinal method for prevention and treatment of equine POI is a combination of three drugs, according to the needs of the individual scheme of each case [5, 14, 32]:

1.Neostigmine methylsulfate (in a dose of 0.004 mg/kg per 2 h, i.e., 2 mg per

2.Metoclopramide (in a dose of 0.01–0.02 mg/kg per 2 h, i.e., 5–10 mg per

We found that the prophylactic perioperative use of these drugs in risk horses to reduce the incidence of POI, and by occurrence of ileus significantly improved survival rate [5, 14, 32]. These prokinetic drugs should not be applied at the same time (little benefit), but strictly in turn. Why these drugs benefit only in turn in combination and not at the same time is unknown. Neostigmine methylsulfate and metoclopramide were applied alternatively between each other in 60 min intervals, so that every horse received each of the drugs every second hour (i.e., 1 h neostigmine methylsulfate was administered and in the second hour metoclopramide was given). We used this therapeutic regimen for POI horses continuously for several days until a result was obtained (complete absence of gastric reflux), and usually, this happened within 24–90 h. The withdrawal of these drugs should take place gradually throughout a few days. On average, this occurred 5–6 days after the onset of equine POI. If sharp withdrawal of these prokinetics is undertaken, a relapse of

Nasogastric decompression is a classic supportive treatment that prevents gastric

Horses without gastric reflux were allowed access to water within 12–18 h after abdominal surgery and were provided with small amounts of feed at 18–30 h after surgery. Initially, small amounts of grass hay or small amounts of bran mash with 100 ml laxatives were fed every 3–4 h. The quantities were gradually increased daily until the horses were allowed to freely eat hay by choice (usually by 21 days after

dilation in horses with POI. We performed this procedure in horses that showed gastric reflux, it was applied regularly every 4–6 h, and most horses begin to show clinical signs (colic) associated with excessive fluid accumulation in the stomach. Retaining an indwelling tube for 12–15 h in horses with POI was performed only in

cases where animals showed extensive stress syndrome by intubation.

*DOI: http://dx.doi.org/10.5772/intechopen.91290*

nation of gastric and intestinal cycles [134].

*6.5.7 Combination of prokinetic drugs*

500 kg BW, subcutaneously)

gastric reflux is possible.

**6.6 Nasogastric decompression**

**6.7 Judicious timing of feeding**

500 kg BW, subcutaneously or intravenously)

3.Domperidone (in a dose of 0.16 mg/kg orally, every 8 h)

*6.5.6 Dopamine antagonist*

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal… DOI: http://dx.doi.org/10.5772/intechopen.91290*

#### *6.5.6 Dopamine antagonist*

*Equine Science*

pelvic flexure activity in healthy ponies [71, 122]. These results suggest that the drug would not be appropriate for gastric and small intestinal problems but may be beneficial for large intestinal motility dysfunction. However, neostigmine increased the amplitude of rhythmic contractions in both the resting and distended jejunum in anesthetized ponies, and it induced contractile activity in the ileum, supporting its use for motility dysfunction in both the small and large intestine [26, 29, 124]. Based on our clinical impressions, neostigmine if used as monotherapy repeated at 60 min intervals (during 24–48 h) has significant beneficial effects in the treatment

Sodium channel blockers—lidocaine is currently a prokinetic agent, which is most frequently used for the treatment of POI in equine practice, although scientific evidence on its prokinetic and analgesic effectiveness is limited [33, 124–128]. Lidocaine has antinociceptive, antihyperalgesic, and anti-inflammatory effects [6, 7]. In an investigation within a UK hospital population, lidocaine therapy had no effect on the prevalence of postoperative reflux, total reflux volume or duration of reflux and as well as no effect on postoperative survival in horses undergoing abdominal surgery [129]. According to our observations, lidocaine if used as monotherapy has little positive effect on the treatment of equine POI and is significantly inferior to a

Drugs acting as 5-hydroxytryptamine receptors include metoclopramide, cisapride, mosapride citrate and tegaserod [36, 130–132]. Metoclopramide hydrochloride (MCP) is a first-generation substituted benzamide whose prokinetic activity is both through dopamine 1 (DA1) and 2 (DA2) receptor antagonism and through 5-HT 4-receptor (5-HT4) agonism and 5-HT3 receptor antagonism [11]. Stimulation of DA2 receptors inhibits the release of acetylcholine, and stimulation of 5-HT4 receptors enhances the release of acetylcholine from the myenteric ganglia. MCP is a drug, which for a long time has often been used in the prevention and treatment of equine POI, but results in published studies have been variable [5, 8, 21, 130]. The prokinetic capacity of metoclopramide appears substantial in the equine stomach, duodenum and jejunum, but not in the large

Motilin agonists include erythromycin lactobionate, and a macrolide antibiotic has been shown to significantly increase solid phase gastric and dose-dependent cacal emptying and is thought to exert prokinetic effects via activation of motilin receptors [20, 21, 36]. The prokinetic effects of erythromycin reported in healthy horses were not the same in horses with gastrointestinal disease [110, 122, 128].

Adrenergic antagonists include acepromazine maleate, a nonselective α-adrenergic antagonist, and yohimbine, tolazamide, and atipamezole, which are selective α2-adrenergic antagonists. Their use as prokinetics is based on the assumption that sympathetic hyperactivity contributes to POI, but their beneficial effects

of colitis cases, but not in POI of the small intestine [43].

*6.5.2 Sodium channel blockers*

combination of prokinetic drugs [32].

intestine [128, 133].

*6.5.4 Motilin agonists*

*6.5.5 Adrenergic antagonists*

are not well understood [6, 7].

*6.5.3 Drugs acting as 5-hydroxytryptamine receptors*

**152**

Dopamine antagonist—domperidone is a selective peripheral DA2 receptor antagonist [26]. In a preliminary experimental model of POI in ponies, domperidone was effective in restoring transit time, electromechanical activity, and coordination of gastric and intestinal cycles [134].

#### *6.5.7 Combination of prokinetic drugs*

Combination of prokinetic drugs—based on our research, the best medicinal method for prevention and treatment of equine POI is a combination of three drugs, according to the needs of the individual scheme of each case [5, 14, 32]:


We found that the prophylactic perioperative use of these drugs in risk horses to reduce the incidence of POI, and by occurrence of ileus significantly improved survival rate [5, 14, 32]. These prokinetic drugs should not be applied at the same time (little benefit), but strictly in turn. Why these drugs benefit only in turn in combination and not at the same time is unknown. Neostigmine methylsulfate and metoclopramide were applied alternatively between each other in 60 min intervals, so that every horse received each of the drugs every second hour (i.e., 1 h neostigmine methylsulfate was administered and in the second hour metoclopramide was given). We used this therapeutic regimen for POI horses continuously for several days until a result was obtained (complete absence of gastric reflux), and usually, this happened within 24–90 h. The withdrawal of these drugs should take place gradually throughout a few days. On average, this occurred 5–6 days after the onset of equine POI. If sharp withdrawal of these prokinetics is undertaken, a relapse of gastric reflux is possible.

#### **6.6 Nasogastric decompression**

Nasogastric decompression is a classic supportive treatment that prevents gastric dilation in horses with POI. We performed this procedure in horses that showed gastric reflux, it was applied regularly every 4–6 h, and most horses begin to show clinical signs (colic) associated with excessive fluid accumulation in the stomach. Retaining an indwelling tube for 12–15 h in horses with POI was performed only in cases where animals showed extensive stress syndrome by intubation.

#### **6.7 Judicious timing of feeding**

Horses without gastric reflux were allowed access to water within 12–18 h after abdominal surgery and were provided with small amounts of feed at 18–30 h after surgery. Initially, small amounts of grass hay or small amounts of bran mash with 100 ml laxatives were fed every 3–4 h. The quantities were gradually increased daily until the horses were allowed to freely eat hay by choice (usually by 21 days after surgery).

Freeman and coworkers were able to show that of the horses taken to surgery for small intestinal disease, only 10% developed postoperative ileus [17]. According to the authors, one key management factor in prophylactic procedures of POI was early re-feeding, where horses were offered water and small amounts of hay within 18–24 h of the completion of surgery for small intestinal disease. Early feeding following abdominal surgery is a commonly applied prophylactic approach in human medicine, as well. It is hypothesized to promote restoration of gastrointestinal motility via the release of neuropeptides in response to solid feed ingestion. In humans, it is known that chewing gum is a type of sham feeding that promotes intestinal motility through cephalic-vagal stimulation [6, 7, 135].

According to our opinion, the judicious timing of feeding in horses with POI is when no signs of reflux are apparent or when motility is regained. Horses with evidence of gastric reflux are unlikely to tolerate enteral feeding and should receive intravenous nutritional support (i.e., glucose solutions and amino acids). In addition to the intravenous administration of glucose solutions, it is necessary to use insulin subcutaneously at a dose of 0.08 U/kg every 12 h in order to block the lipase enzyme responsible for releasing triglycerides from fat depots. As is well known, if the fasting regime lasts more than 3 days, this may provoke development of a severe form of equine hyperlipidemia, notable in obese horses. Hyperlipidemia is associated with periods of negative energy balance and physiologic stress [136]. For this reason, in horses with POI at 48 h after abdominal surgery, regardless of the presence of gastric reflux, we allowed the horses, after nasogastric decompression, to be fed with a small amount of bran mash with ranitidine oral tables (H2 antihistamine). Additionally, for horses with gastric reflux for which the provision of enteral nutrition is not possible, the provision of a lick (e.g., mineral block) has been suggested as a form of sham feeding, equivalent to gum chewing in humans.

#### **6.8 Stress reduction strategies**

Suppression of parasympathetic activity and hyperactivity of the sympathetic nervous system with activation of the hypothalamic-pituitary-adrenal axis (stress syndrome) has a very important role in the development of equine POI (as discussed above). Causes of equine stress syndrome in perioperative period can be varied, primarily pain and inflammation, but also recovery from anesthesia, postoperative diagnostic and management procedures and fasting, as well as different psychological (fear) factors. It is generally considered or hypothesized that a more invasive surgery, with extensive tissue trauma and noxious stimuli, triggers a more significant stress response. After surgery, the horse is placed in an unfamiliar environment with unknown caretakers and probably starved while having additional pain to deal with. Postoperative pain can originate from peritoneal inflammation and abdominal incision. Consequently, it is important on all occasions to consider minimizing sympathetic activity, primarily pain and inflammation control of the horses after abdominal surgery. As is well known, anti-inflammatory drugs lead to lower pain scores and lower plasma cortisol levels [82, 91]. This amount of stress modulates the pain perception and adds further to the perceived pain. This in turn increases appetite, so the horse does not enter a catabolic state in order to produce substrates for healing.

Given all of the stress, it is therefore also extremely important to take care of the horse psychologically. All therapeutic procedures in postoperative period should be performed with minimal stress. Stress-enhancing procedures may include introduction of a nasogastric tube into the stomach, which causes discomfort and the release of catecholamine, and this process is necessarily carried out with the imposition of

**155**

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal…*

a twitch and without sedation. It is believed that a twitch calms the horse by releasing endorphins as pressure is applied, thus reducing stress and pain. Administration

pharmacologic mechanisms for reducing the stress response are quite successful, for instance, regular visits from the owner or a familiar caretaker, frequent contact and grooming preferably by the same handler or veterinarian, short periods of handwalking, treats given from time to time, short periods of grazing (1–2 min around 24–48 h after abdominal surgery) and minimal enteral nutrition. As described above, early re-feeding has been attributed to possible downregulation of the metabolic stress response [35]. Additionally, all other external stress factors for horses (including transport, loud noises, bright light and rudeness of medical staff), as far as possible, should be abolished during the postoperative period in an equine clinic, both in horses with a risk of development and also in horses that already have a POI.

Relaparotomy (repeat celiotomy) is widely accepted as a treatment option in the management of postoperative colic and ileus [6, 7]. A repeated surgical intervention in the abdominal cavity may correct technical errors that occurred during the first surgery and solve conservatively unsolvable motility disorders as well as pathological conditions that occur in the post-surgical period without a clear relation to the first intervention [1]. Previously, authors considered that intestinal manipulation (massage) and repeated enterotomy likely have beneficial effects to equine POI [103]. However, the potential benefit of limiting the degree of intestinal manipulation in equine surgery must be weighed against the increased risk of other postoperative complications (postanesthetic myopathy, wound infection and hernia). According to our observation, repeat celiotomy did not increase survival rate in horses with POI; for example, surgical cases had a lower survival rate than

Albert A. Rizvanov was supported by the Russian Government Program of Competitive Growth of Kazan Federal University and funded by state assignments 20.5175.2017/6.7 and 17.9783.2017/8.9 of the Ministry of Science and Higher

This chapter is dedicated to Prof. Dr. Dr. H.C. Bernhard Huskamp (1932–2018)

the founder of the Veterinary clinic Hochmoor in recognition of his extensive

of corticosteroid drugs results in the reduction of stress syndrome, but non-

*DOI: http://dx.doi.org/10.5772/intechopen.91290*

**6.9 Repeat celiotomy and postoperative ileus**

medically managed cases of POI [32].

Education of Russian Federation.

contributions to equine colic surgery.

The authors declare no conflicts of interest.

**Acknowledgements**

**Conflicts of interest**

**Dedication**

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal… DOI: http://dx.doi.org/10.5772/intechopen.91290*

a twitch and without sedation. It is believed that a twitch calms the horse by releasing endorphins as pressure is applied, thus reducing stress and pain. Administration of corticosteroid drugs results in the reduction of stress syndrome, but nonpharmacologic mechanisms for reducing the stress response are quite successful, for instance, regular visits from the owner or a familiar caretaker, frequent contact and grooming preferably by the same handler or veterinarian, short periods of handwalking, treats given from time to time, short periods of grazing (1–2 min around 24–48 h after abdominal surgery) and minimal enteral nutrition. As described above, early re-feeding has been attributed to possible downregulation of the metabolic stress response [35]. Additionally, all other external stress factors for horses (including transport, loud noises, bright light and rudeness of medical staff), as far as possible, should be abolished during the postoperative period in an equine clinic, both in horses with a risk of development and also in horses that already have a POI.

#### **6.9 Repeat celiotomy and postoperative ileus**

Relaparotomy (repeat celiotomy) is widely accepted as a treatment option in the management of postoperative colic and ileus [6, 7]. A repeated surgical intervention in the abdominal cavity may correct technical errors that occurred during the first surgery and solve conservatively unsolvable motility disorders as well as pathological conditions that occur in the post-surgical period without a clear relation to the first intervention [1]. Previously, authors considered that intestinal manipulation (massage) and repeated enterotomy likely have beneficial effects to equine POI [103]. However, the potential benefit of limiting the degree of intestinal manipulation in equine surgery must be weighed against the increased risk of other postoperative complications (postanesthetic myopathy, wound infection and hernia). According to our observation, repeat celiotomy did not increase survival rate in horses with POI; for example, surgical cases had a lower survival rate than medically managed cases of POI [32].

#### **Acknowledgements**

*Equine Science*

**6.8 Stress reduction strategies**

Freeman and coworkers were able to show that of the horses taken to surgery for small intestinal disease, only 10% developed postoperative ileus [17]. According to the authors, one key management factor in prophylactic procedures of POI was early re-feeding, where horses were offered water and small amounts of hay within 18–24 h of the completion of surgery for small intestinal disease. Early feeding following abdominal surgery is a commonly applied prophylactic approach in human medicine, as well. It is hypothesized to promote restoration of gastrointestinal motility via the release of neuropeptides in response to solid feed ingestion. In humans, it is known that chewing gum is a type of sham feeding that promotes

According to our opinion, the judicious timing of feeding in horses with POI is when no signs of reflux are apparent or when motility is regained. Horses with evidence of gastric reflux are unlikely to tolerate enteral feeding and should receive intravenous nutritional support (i.e., glucose solutions and amino acids). In addition to the intravenous administration of glucose solutions, it is necessary to use insulin subcutaneously at a dose of 0.08 U/kg every 12 h in order to block the lipase enzyme responsible for releasing triglycerides from fat depots. As is well known, if the fasting regime lasts more than 3 days, this may provoke development of a severe form of equine hyperlipidemia, notable in obese horses. Hyperlipidemia is associated with periods of negative energy balance and physiologic stress [136]. For this reason, in horses with POI at 48 h after abdominal surgery, regardless of the presence of gastric reflux, we allowed the horses, after nasogastric decompression, to be fed with a small amount of bran mash with ranitidine oral tables (H2 antihistamine). Additionally, for horses with gastric reflux for which the provision of enteral nutrition is not possible, the provision of a lick (e.g., mineral block) has been suggested as a form of sham feeding, equivalent to gum chewing in humans.

Suppression of parasympathetic activity and hyperactivity of the sympathetic nervous system with activation of the hypothalamic-pituitary-adrenal axis (stress syndrome) has a very important role in the development of equine POI (as discussed above). Causes of equine stress syndrome in perioperative period can be varied, primarily pain and inflammation, but also recovery from anesthesia, postoperative diagnostic and management procedures and fasting, as well as different psychological (fear) factors. It is generally considered or hypothesized that a more invasive surgery, with extensive tissue trauma and noxious stimuli, triggers a more significant stress response. After surgery, the horse is placed in an unfamiliar environment with unknown caretakers and probably starved while having additional pain to deal with. Postoperative pain can originate from peritoneal inflammation and abdominal incision. Consequently, it is important on all occasions to consider minimizing sympathetic activity, primarily pain and inflammation control of the horses after abdominal surgery. As is well known, anti-inflammatory drugs lead to lower pain scores and lower plasma cortisol levels [82, 91]. This amount of stress modulates the pain perception and adds further to the perceived pain. This in turn increases appetite, so the horse does not enter a catabolic state in order to produce

Given all of the stress, it is therefore also extremely important to take care of the horse psychologically. All therapeutic procedures in postoperative period should be performed with minimal stress. Stress-enhancing procedures may include introduction of a nasogastric tube into the stomach, which causes discomfort and the release of catecholamine, and this process is necessarily carried out with the imposition of

intestinal motility through cephalic-vagal stimulation [6, 7, 135].

**154**

substrates for healing.

Albert A. Rizvanov was supported by the Russian Government Program of Competitive Growth of Kazan Federal University and funded by state assignments 20.5175.2017/6.7 and 17.9783.2017/8.9 of the Ministry of Science and Higher Education of Russian Federation.

#### **Conflicts of interest**

The authors declare no conflicts of interest.

#### **Dedication**

This chapter is dedicated to Prof. Dr. Dr. H.C. Bernhard Huskamp (1932–2018) the founder of the Veterinary clinic Hochmoor in recognition of his extensive contributions to equine colic surgery.

*Equine Science*

#### **Author details**

Milomir Kovac1 \*, Ruslan Aliev1 , Sergey Pozyabin1 , Nevena Drakul1 and Albert Rizvanov2

1 Veterinary Clinic "New Century", Moscow State Academy of Veterinary Medicine and Biotechnology, Moscow, Russia

2 Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russia

\*Address all correspondence to: kovacmilomir@gmail.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**157**

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal…*

Journal. 1986;**18**(4):249-255. DOI: 10.1111/j.2042-3306.1986.tb03618.x

[9] Kovac M, Aliev R, Tigina O,

Diagnosis and treatment. Vet Pharmaceuticals. 2015;**3**:84-86

Ivanatov E. Equine large colon volvulus.

[10] Jain D. Neuromuscular disorders of the GI tract. In: Odze RO, Goldblum JR, editors. Surgical Pathology of the GI Tract, Liver, Biliary Tract, and Pancreas. 2nd ed. USA: Elsevier; 2009. pp. 125-143

[11] Gannon RH. Current strategies for preventing or ameliorating postoperative ileus: A multimodal approah. American Journal of Health-System Pharmacy. 2007;**64**:S8-S12. DOI:

[12] Bauer AJ, Schwarz NT, Moore BA,

[13] Kehlet H, Holte K. Review of postoperative ileus. American Journal of Surgery. 2001;**182**(5a):3s-10s. DOI: 10.1016/S0002-9610(01)00781-4

[14] Kovac M, Aliev R, Elizarova O, Ivanyatov E. Etiology, diagnosis and treatment of equine paralytic ileus. Vet

Pharmaceuticals. 2015;**4**:26-28

[15] Blikslager AT, Bowman KF, Levine JF, Bristol DG, Roberts MC. Evaluation of factors associated with postoperative ileus in horses: 31 cases (1990-1992). Journal of the American Veterinary Medical Association.

[16] Freeman DE, Hammock P, Baker GJ, Goetz T, Foreman JH, Schaeffer DJ, et al. Short- and long-term survival and prevalence of postoperative ileus after small intestinal surgery in the horse.

1994;**205**(12):1748-1752

10.2146/ajhp070429

Turler A, Kalff JC. Ileus in critical illness: Mechanisms and management. Current Opinion in Critical Care. 2002;**8**(2):152-157. DOI: 10.1097/00075198-200204000-00011

*DOI: http://dx.doi.org/10.5772/intechopen.91290*

[1] Mair TS, Smith LJ, Sherlock CE. Evidence-based gastrointestinal surgery

[2] Dukti S, White NA. Prognosticating equine colic. Veterinary Clinics of North America: Equine Practice. 2009;**25**(2):217. DOI: 10.1016/j.

[3] French NP, Smith J, Edwards GB, Proudman CJ. Equine surgical colic: Risk factors for postoperative complications.

Equine Veterinary Journal. 2002;**34**(5):444-449. DOI: 10.2746/042516402776117791

[4] Kovac M. Colic Horse: Cause, Diagnosis, Treatment. Moscow, Russia:

[5] Aliev R, Pozabin SV. Treatment method for horses with postoperative paralytic ileus. Journal Veterinaria I Kormlenie. 2019;**2**:28-30. DOI: 10.30917/

[6] Siciliano S. Paralytischer Ileus und Reperfusionsstörung beim Pferd. Literaturübersicht und retrospektive Fallanalyse. Berlin: Freie University;

ATT-VK-1814-9588-2019-2-10

[7] Traut U, Brugger L, Kunz R, Pauli-Magnus C, Haug K, Bucher HC, et al. Systemic prokinetic pharmacologic treatment for postoperative adynamic ileus following abdominal surgery in adults. Cochrane Database of

[8] Gerring EEL, Hunt JM. Pathophysiology of equine postoperative ileus—Effect of

Systematic Reviews. 2009;(4):1-85. DOI: 10.1002/14651858.CD004930.pub3

adrenergic-blockade, parasympathetic stimulation and metoclopramide in an experimental-model. Equine Veterinary

in horses. Veterinary Clinics of North America: Equine Practice. 2007;**23**(2):267. DOI: 10.1016/j.

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**Author details**

Milomir Kovac1

Kazan, Russia

and Albert Rizvanov2

\*, Ruslan Aliev1

and Biotechnology, Moscow, Russia

provided the original work is properly cited.

, Sergey Pozyabin1

1 Veterinary Clinic "New Century", Moscow State Academy of Veterinary Medicine

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 Institute of Fundamental Medicine and Biology, Kazan Federal University,

\*Address all correspondence to: kovacmilomir@gmail.com

, Nevena Drakul1

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*Equine Science*

3306.2000.tb05333.x

Equine Veterinary Journal. Supplement. 2000;(32):42-51. DOI: 10.1111/j.2042[24] Lomax AE, Sharkey KA, Furness JB. The participation of the sympathetic innervation of the gastrointestinal tract in disease states. Neurogastroenterology and Motility. 2010;**22**(1):7-18. DOI: 10.1111/j.1365-2982.2009.01381.x

[25] Antonioli L, Fornai M, Colucci R, Ghisu N, Tuccori M, Del Tacca M, et al. Regulation of enteric functions by adenosine: pathophysiological and pharmacological implications. Pharmacology & Therapeutics. 2008;**120**(3):233-253. DOI: 10.1016/j.

[26] Damen S. A Review on Prokinetics, Splasmolytics and Their Receptors. Belgium: Faculty of Veterinary Medicine, Ghent University; 2016

[27] Rakestraw PC. Intestinal motility and transit. In: White NA, Moore JN, Mair TS, editors. The Equine Acute Abdomen. Jackson, USA: Teton New

[28] Schwarz NT, Simmons RL. Minor intraabdominal injury followed by low dose LPS administration act synergistically to induce ileus. Neurogastroenterology and Motility.

[29] Wong DM, Davis JL, White NA. Motility of the equine gastrointestinal tract: Physiology and pharmacotherapy.

Equine Veterinary Education. 2011;**23**(2):88-100. DOI:

10.1111/j.2042-3292.2010.00173.x

[30] Mcconalogue K, Furness JB. Gastrointestinal neurotransmitters. Baillière's Clinical Endocrinology and Metabolism. 1994;**8**(1):51-76. DOI: 10.1016/S0950-351x(05)80226-5

[31] Cohen ND, Lester GD, Sanchez LC, Merritt AM, Roussel AJ Jr. Evaluation of risk factors associated with development of postoperative ileus in horses. Journal of the American Veterinary Medical Association. 2004;**225**(7):1070-1078. DOI: 10.2460/javma.2004.225.1070

pharmthera.2008.08.010

Media; 2008. pp. 67-91

2000;**11**(2):288

[17] Freeman DE. Post operative ileus (POI): Another perspective. Equine Veterinary Journal. 2008;**40**(4):297-298. DOI: 10.2746/042516408X302528

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[104] Lester GD, Bolton JR, Cullen LK, Thurgate SM. Effects of generalanesthesia on myoelectric activity of the intestine in horses. American Journal of Veterinary Research. 1992;**53**(9):1553-1557

[105] Schurizek BA, Willacy LH, Kraglund K, Andreasen F, Juhl B. Effects of general anaesthesia with halothane on antroduodenal motility, pH and gastric emptying rate in man. British Journal of Anaesthesia. 1989;**62**(2):129- 137. DOI: 10.1093/bja/62.2.129

[106] Little D, Redding WR, Blikslager AT. Risk factors for reduced postoperative fecal output in horses: 37 cases (1997-1998). Journal of the American Veterinary Medical Association. 2001;**218**(3):414-420. DOI: 10.2460/javma.2001.218.414

[107] Salciccia A, Gougnard A, Grulke S, de Pouyade GD, Libertiaux V, Busoni V, et al. Gastrointestinal effects of general

anaesthesia in horses undergoing non abdominal surgery: Focus on the clinical parameters and ultrasonographic images. Research in Veterinary Science. 2019;**124**:123-128. DOI: 10.1016/j. rvsc.2019.03.011

[108] Lefebvre D, Hudson NPH, Elce YA, Blikslager A, Divers TJ, Handel IG, et al. Clinical features and management of equine post operative ileus (POI): Survey of Diplomates of the American Colleges of Veterinary Internal Medicine (ACVIM), Veterinary Surgeons (ACVS) and Veterinary Emergency and Critical Care (ACVECC). Equine Veterinary Journal. 2016;**48**(6):714-719. DOI: 10.1111/evj.12520

[109] Lefebvre D, Pirie RS, Handel IG, Tremaine WH, Hudson NPH. Clinical features and management of equine post operative ileus: Survey of diplomates of the European Colleges of Equine Internal Medicine (ECEIM) and Veterinary Surgeons (ECVS). Equine Veterinary Journal. 2016;**48**(2):182-187. DOI: 10.1111/evj.12355

[110] Roussel AJ, Cohen ND, Hooper RN, Rakestraw PC. Risk factors associated with development of postoperative ileus in horses. Journal of the American Veterinary Medical Association. 2001;**219**(1):72-78. DOI: 10.2460/ javma.2001.219.72

[111] Merritt AM, Blikslager AT. Post operative ileus: To be or not to be? Equine Veterinary Journal. 2008;**40**(4):295-296. DOI: 10.2746/042516408X302537

[112] Mitchell CF, Malone ED, Sage AM, Niksich K. Evaluation of gastrointestinal activity patterns in healthy horses using B mode and Doppler ultrasonography. The Canadian Veterinary Journal. 2005;**46**(2):134-140

[113] Kovac M, Aliev R, Tkacenko A. Improved methodology of abdominal ultrasonography in horses with

**165**

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal…*

[120] Lim R, Morrill JM, Lynch RC, Reed KL, Gower AC, Leeman SE, et al. Practical limitations of bioresorbable membranes in the prevention of intra-abdominal adhesions. Journal of Gastrointestinal Surgery. 2009;**13**(1):35- 42. DOI: 10.1007/s11605-008-0724-3

[121] Kuebelbeck KL, Slone DE, May KA. Effect of omentectomy on adhesion formation in horses. Veterinary Surgery. 1998;**27**(2):132-137. DOI: 10.1111/j.1532-950X.1998.tb00109.x

[122] Smith MA, Edwards GB, Dallap BL, Cripps PJ, Proudman CJ. Evaluation of the clinical efficacy of prokinetic drugs in the management of post-operative ileus: Can retrospective data help us? Veterinary Journal. 2005;**170**(2):230-236. DOI: 10.1016/j.

[123] van der Spoel JI, Oudemansvan Straaten HM, Stoutenbeek CP, Bosman RJ, Zandstra DF. Neostigmine resolves critical illness-related colonic ileus in intensive care patients with multiple organ failure—a prospective, double-blind, placebo-controlled trial. Intensive Care Medicine. 2001;**27**(5):822-827. DOI: 10.1007/

[124] Van Hoogmoed LM, Nieto JE, Snyder JR, Harmon FA. Survey of prokinetic use in horses with gastrointestinal injury. Veterinary Surgery. 2004;**33**(3):279-285. DOI: 10.1111/j.1532-950X.2004.04041.x

[125] Milligan M, Beard W, Kukanich B, Sobering T, Waxman S. The effect of lidocaine on postoperative jejunal motility in normal horses. Veterinary Surgery. 2007;**36**(3):214-220. DOI: 10.1111/j.1532-950X.2007.00255.x

[126] Brianceau P, Chevalier H, Karas A, Court MH, Bassage L, Kirker-Head C, et al. Intravenous lidocaine and small-intestinal size, abdominal fluid, and outcome after colic surgery in

tvjl.2004.06.006

s001340100926

*DOI: http://dx.doi.org/10.5772/intechopen.91290*

gastrointestinal disease. Veterinár̆ství. 2018;**5**:31-37. Availabel from: http:// vetpharma.org/articles/140/7827/

[114] Freeman SL, England GC. Effect of romifidine on gastrointestinal motility, assessed by transrectal ultrasonography. Equine

Veterinary Journal. 2001;**33**(6):570- 6.10.2746/042516401776563436

McDonell WN, Kerr CL, Neto FJT, Mirakhur KK. Comparison of

hemodynamic, clinicopathologic, and gastrointestinal motility effects and recovery characteristics of anesthesia with isoflurane and halothane in horses undergoing arthroscopic surgery. American Journal of Veterinary Research. 2006;**67**(1):32-42. DOI:

[115] Durongphongtorn S,

10.2460/ajvr.67.1.32

2018;**59**(1):67-73

cveq.2009.05.003

10.1155/2014/279730

[116] Phillips TJ, Walmsley JP.

[117] Bracamonte JL, Devick I,

Retrospective analysis of the results of 151 exploratory laparotomies in horses with gastrointestinal-disease. Equine Veterinary Journal. 1993;**25**(5):427-431. DOI: 10.1111/j.2042-3306.1993.tb02985.x

Thomas KL, Hendrick S. Comparison of hand-sewn and oversewn stapled jejunojejunal anastomoses in horses. The Canadian Veterinary Journal.

[118] Klohnen A. New perspectives in postoperative complications after abdominal surgery. Veterinary Clinics of North America: Equine Practice. 2009;**25**(2):341. DOI: 10.1016/j.

[119] Alonso Jde M, Alves AL, Watanabe MJ, Rodrigues CA, Hussni CA. Peritoneal response to abdominal surgery: The role of equine abdominal adhesions and current prophylactic strategies. Vet Med Int. 2014;**2014**:279730. DOI:

*Current Strategies for Prevention and Treatment of Equine Postoperative Ileus: A Multimodal… DOI: http://dx.doi.org/10.5772/intechopen.91290*

gastrointestinal disease. Veterinár̆ství. 2018;**5**:31-37. Availabel from: http:// vetpharma.org/articles/140/7827/

*Equine Science*

1998;**59**(5):619-623

1998;**59**(3):320-327

1984;**45**(4):795-799

1992;**53**(9):1553-1557

[105] Schurizek BA, Willacy LH,

137. DOI: 10.1093/bja/62.2.129

[106] Little D, Redding WR,

10.2460/javma.2001.218.414

Kraglund K, Andreasen F, Juhl B. Effects of general anaesthesia with halothane on antroduodenal motility, pH and gastric emptying rate in man. British Journal of Anaesthesia. 1989;**62**(2):129-

Blikslager AT. Risk factors for reduced postoperative fecal output in horses: 37 cases (1997-1998). Journal of the American Veterinary Medical Association. 2001;**218**(3):414-420. DOI:

[107] Salciccia A, Gougnard A, Grulke S, de Pouyade GD, Libertiaux V, Busoni V, et al. Gastrointestinal effects of general

p. 674-679.

Journal of Veterinary Research.

anaesthesia in horses undergoing non abdominal surgery: Focus on the clinical parameters and ultrasonographic images. Research in Veterinary Science. 2019;**124**:123-128. DOI: 10.1016/j.

[108] Lefebvre D, Hudson NPH, Elce YA, Blikslager A, Divers TJ, Handel IG, et al. Clinical features and management of equine post operative ileus (POI): Survey of Diplomates of the American Colleges of Veterinary Internal Medicine (ACVIM), Veterinary Surgeons (ACVS) and Veterinary Emergency and Critical Care (ACVECC). Equine Veterinary Journal. 2016;**48**(6):714-719. DOI:

[109] Lefebvre D, Pirie RS, Handel IG, Tremaine WH, Hudson NPH. Clinical features and management of equine post operative ileus: Survey of

diplomates of the European Colleges of Equine Internal Medicine (ECEIM) and Veterinary Surgeons (ECVS). Equine Veterinary Journal. 2016;**48**(2):182-187.

[110] Roussel AJ, Cohen ND, Hooper RN, Rakestraw PC. Risk factors associated with development of postoperative ileus in horses. Journal of the American Veterinary Medical Association. 2001;**219**(1):72-78. DOI: 10.2460/

rvsc.2019.03.011

10.1111/evj.12520

DOI: 10.1111/evj.12355

javma.2001.219.72

2005;**46**(2):134-140

[111] Merritt AM, Blikslager AT. Post operative ileus: To be or not to be? Equine Veterinary Journal. 2008;**40**(4):295-296. DOI: 10.2746/042516408X302537

[112] Mitchell CF, Malone ED, Sage AM, Niksich K. Evaluation of gastrointestinal activity patterns in healthy horses using B mode and Doppler ultrasonography. The Canadian Veterinary Journal.

[113] Kovac M, Aliev R, Tkacenko A. Improved methodology of abdominal ultrasonography in horses with

[101] Lester GD, Merritt AM, Neuwirth L, Vetro-Widenhouse T, Steible C, Rice B. Effect of alpha(2)-

adrenergic, cholinergic, and

nonsteroidal anti-inflammatory drugs on myoelectric activity of ileum, cecum, and right ventral colon and on cecal emptying of radiolabeled markers in clinically normal ponies. American Journal of Veterinary Research.

[102] Adams SB, Lamar CH, Masty J. Motility of the distal portion of the jejunum and pelvic flexure in ponies: Effects of six drugs. American Journal of Veterinary Research.

[103] Lester G. Gastrointestinal ileus. In: Smith B, editor. Large Animal Internal Medicine. St. Louis, USA: Mosby; 2002.

[104] Lester GD, Bolton JR, Cullen LK, Thurgate SM. Effects of generalanesthesia on myoelectric activity of the intestine in horses. American Journal of Veterinary Research.

**164**

[114] Freeman SL, England GC. Effect of romifidine on gastrointestinal motility, assessed by transrectal ultrasonography. Equine Veterinary Journal. 2001;**33**(6):570- 6.10.2746/042516401776563436

[115] Durongphongtorn S, McDonell WN, Kerr CL, Neto FJT, Mirakhur KK. Comparison of hemodynamic, clinicopathologic, and gastrointestinal motility effects and recovery characteristics of anesthesia with isoflurane and halothane in horses undergoing arthroscopic surgery. American Journal of Veterinary Research. 2006;**67**(1):32-42. DOI: 10.2460/ajvr.67.1.32

[116] Phillips TJ, Walmsley JP. Retrospective analysis of the results of 151 exploratory laparotomies in horses with gastrointestinal-disease. Equine Veterinary Journal. 1993;**25**(5):427-431. DOI: 10.1111/j.2042-3306.1993.tb02985.x

[117] Bracamonte JL, Devick I, Thomas KL, Hendrick S. Comparison of hand-sewn and oversewn stapled jejunojejunal anastomoses in horses. The Canadian Veterinary Journal. 2018;**59**(1):67-73

[118] Klohnen A. New perspectives in postoperative complications after abdominal surgery. Veterinary Clinics of North America: Equine Practice. 2009;**25**(2):341. DOI: 10.1016/j. cveq.2009.05.003

[119] Alonso Jde M, Alves AL, Watanabe MJ, Rodrigues CA, Hussni CA. Peritoneal response to abdominal surgery: The role of equine abdominal adhesions and current prophylactic strategies. Vet Med Int. 2014;**2014**:279730. DOI: 10.1155/2014/279730

[120] Lim R, Morrill JM, Lynch RC, Reed KL, Gower AC, Leeman SE, et al. Practical limitations of bioresorbable membranes in the prevention of intra-abdominal adhesions. Journal of Gastrointestinal Surgery. 2009;**13**(1):35- 42. DOI: 10.1007/s11605-008-0724-3

[121] Kuebelbeck KL, Slone DE, May KA. Effect of omentectomy on adhesion formation in horses. Veterinary Surgery. 1998;**27**(2):132-137. DOI: 10.1111/j.1532-950X.1998.tb00109.x

[122] Smith MA, Edwards GB, Dallap BL, Cripps PJ, Proudman CJ. Evaluation of the clinical efficacy of prokinetic drugs in the management of post-operative ileus: Can retrospective data help us? Veterinary Journal. 2005;**170**(2):230-236. DOI: 10.1016/j. tvjl.2004.06.006

[123] van der Spoel JI, Oudemansvan Straaten HM, Stoutenbeek CP, Bosman RJ, Zandstra DF. Neostigmine resolves critical illness-related colonic ileus in intensive care patients with multiple organ failure—a prospective, double-blind, placebo-controlled trial. Intensive Care Medicine. 2001;**27**(5):822-827. DOI: 10.1007/ s001340100926

[124] Van Hoogmoed LM, Nieto JE, Snyder JR, Harmon FA. Survey of prokinetic use in horses with gastrointestinal injury. Veterinary Surgery. 2004;**33**(3):279-285. DOI: 10.1111/j.1532-950X.2004.04041.x

[125] Milligan M, Beard W, Kukanich B, Sobering T, Waxman S. The effect of lidocaine on postoperative jejunal motility in normal horses. Veterinary Surgery. 2007;**36**(3):214-220. DOI: 10.1111/j.1532-950X.2007.00255.x

[126] Brianceau P, Chevalier H, Karas A, Court MH, Bassage L, Kirker-Head C, et al. Intravenous lidocaine and small-intestinal size, abdominal fluid, and outcome after colic surgery in

horses. Journal of Veterinary Internal Medicine. 2002;**16**(6):736-741. DOI: 10.1892/0891-6640(2002)016<0736:ilas sa>2.3.co;2

[127] Freeman DE. Is there still a place for lidocaine in the (postoperative) management of colics? Veterinary Clinics of North America: Equine Practice. 2019;**35**(2):275. DOI: 10.1016/j. cveq.2019.03.003

[128] Nieto JE, Rakestraw PC, Snyder JR, Vatistas NJ. In vitro effects of erythromycin, lidocaine, and metoclopramide on smooth muscle from the pyloric antrum, proximal portion of the duodenum, and middle portion of the jejunum of horses. American Journal of Veterinary Research. 2000;**61**(4):413-419. DOI: 10.2460/ajvr.2000.61.413

[129] Salem SE, Proudman CJ, Archer DC. Has intravenous lidocaine improved the outcome in horses following surgical management of small intestinal lesions in a UK hospital population? BMC Veterinary Research. 2016;**12**:1-11. DOI: 10.1186/ s12917-016-0784-7

[130] Dart AJ, Hodgson DR. Role of prokinetic drugs for treatment of postoperative ileus in the horse. Australian Veterinary Journal. 1998;**76**(1):25-31

[131] Gerring EL, King JN. Cisapride in the prophylaxis of equine post operative ileus. Equine Veterinary Journal. Supplement. 1989;**21**(S7):52-55. DOI: 10.1111/j.2042-3306.1989.tb05656.x

[132] Sojka JE, Adams SB, Lamar CH, Eller LL. Effect of butorphanol, pentazocine, meperidine, or metoclopramide on intestinal motility in female ponies. American Journal of Veterinary Research. 1988;**49**(4):527-529

[133] Doherty TJ, Andrews FM, Abraha TW, Osborne D, Frazier DL. Metoclopramide ameliorates the effects of endotoxin on gastric emptying of acetaminophen in horses. Canadian Journal of Veterinary Research. 1999;**63**(1):37-40

[134] Nieto JE, Maher O, Stanley SD, Larson R, Snyder JR. In vivo and in vitro evaluation of the effects of domperidone on the gastrointestinal tract of healthy horses. American Journal of Veterinary Research. 2013;**74**(8):1103-1110

[135] Holte K, Kehlet H. Postoperative ileus: a preventable event. British Journal of Surgery. 2000;**87**(11):1480-1493. DOI: 10.1046/j.1365-2168.2000.01595.x

[136] McKenzie HC. Equine hyperlipidemias. Veterinary Clinics of North America: Equine Practice. 2011;**27**(1):59. DOI: 10.1016/j. cveq.2010.12.008

**167**

**Chapter 9**

*Arbab Sikandar*

lighted in the chapter.

microscope, donkey

**1. Introduction**

**Abstract**

Morphophysiological Study of

In most of the developing countries, donkeys are used to carry goods and water and to guard herds as a livestock guardian. Donkeys possessed a good digestive system and are being offered only low-cost fibers diet like hay and straw. Despite the biological potential of the donkey, only a few studies have focused on the morphophysiological aspects of their digestive system. A series of tubular organs and associated glands are present in the digestive system. Although generally the morphology of the donkey digestive system is comparable to the horse, few dissimilarities exist among such species. In this chapter, we tried to highlight the anatomy, histology and physiology of the digestive system of domestic donkeys including tongue (mucosa, papillae, muscle, taste buds), teeth, pharynx, esophagus, stomach, saccus cecus, descending part, an ascending part and transversal part of the duodenum, jejunum, ileum, cecum, colon (right dorsal and ventral; left dorsal and ventral), rectum and anal canal. The microarchitecture of the tunica mucosa, next to the lumen, is focused upon. Morphology of the large accessary digestive glands viz. salivary gland, liver and pancreas were also highlighted. These structures are situated away from the gut-tubular system but are attached to its lumen through their specified duct system. Furthermore, peculiar microstructures of the internal layers, immune system and microbiome of the gut were correspondingly high-

**Keywords:** anatomy, histology, physiology, oral cavity, stomach, intestine, glands,

Donkey (*Equus africanus asinus*) belongs to Equidae family like horse and is domesticated in most parts of the world [1]. The African wild ass living wildly has been declared as wild ancestor of today's donkey. The life span of donkeys is generally ranging from 25 to 50 years. It is known to have been used as a beast of burden. "The first findings of donkey came from ancient art and archeological records. Donkeys bred and produced mule's offspring which were used by the Spanish during their occupations and defeats. By the same time the donkeys got progressively significance in America and were used for shipping gold around

**1.1 Donkey in the past, present and future perspective**

Gastrointestinal Tract of the

Donkey (*Equus asinus*)

#### **Chapter 9**

*Equine Science*

sa>2.3.co;2

cveq.2019.03.003

[128] Nieto JE, Rakestraw PC,

DOI: 10.2460/ajvr.2000.61.413

[129] Salem SE, Proudman CJ,

[130] Dart AJ, Hodgson DR. Role of prokinetic drugs for treatment of postoperative ileus in the horse. Australian Veterinary Journal.

[131] Gerring EL, King JN. Cisapride in the prophylaxis of equine post operative

[132] Sojka JE, Adams SB, Lamar CH, Eller LL. Effect of butorphanol, pentazocine, meperidine, or metoclopramide on intestinal motility in female ponies. American Journal of Veterinary Research.

ileus. Equine Veterinary Journal. Supplement. 1989;**21**(S7):52-55. DOI: 10.1111/j.2042-3306.1989.tb05656.x

s12917-016-0784-7

1998;**76**(1):25-31

1988;**49**(4):527-529

[133] Doherty TJ, Andrews FM, Abraha TW, Osborne D, Frazier DL.

Archer DC. Has intravenous lidocaine improved the outcome in horses following surgical management of small intestinal lesions in a UK hospital population? BMC Veterinary Research. 2016;**12**:1-11. DOI: 10.1186/

Snyder JR, Vatistas NJ. In vitro effects of erythromycin, lidocaine, and

metoclopramide on smooth muscle from the pyloric antrum, proximal portion of the duodenum, and middle portion of the jejunum of horses. American Journal of Veterinary Research. 2000;**61**(4):413-419.

horses. Journal of Veterinary Internal Medicine. 2002;**16**(6):736-741. DOI: 10.1892/0891-6640(2002)016<0736:ilas Metoclopramide ameliorates the effects of endotoxin on gastric emptying of acetaminophen in horses. Canadian Journal of Veterinary Research.

[134] Nieto JE, Maher O, Stanley SD, Larson R, Snyder JR. In vivo and in vitro evaluation of the effects of domperidone on the gastrointestinal tract of healthy horses. American Journal of Veterinary

Research. 2013;**74**(8):1103-1110

ileus: a preventable event. British Journal of Surgery. 2000;**87**(11):1480-1493. DOI: 10.1046/j.1365-2168.2000.01595.x

[136] McKenzie HC. Equine

cveq.2010.12.008

hyperlipidemias. Veterinary Clinics of North America: Equine Practice. 2011;**27**(1):59. DOI: 10.1016/j.

[135] Holte K, Kehlet H. Postoperative

1999;**63**(1):37-40

[127] Freeman DE. Is there still a place for lidocaine in the (postoperative) management of colics? Veterinary Clinics of North America: Equine Practice. 2019;**35**(2):275. DOI: 10.1016/j.

**166**

## Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*)

*Arbab Sikandar*

#### **Abstract**

In most of the developing countries, donkeys are used to carry goods and water and to guard herds as a livestock guardian. Donkeys possessed a good digestive system and are being offered only low-cost fibers diet like hay and straw. Despite the biological potential of the donkey, only a few studies have focused on the morphophysiological aspects of their digestive system. A series of tubular organs and associated glands are present in the digestive system. Although generally the morphology of the donkey digestive system is comparable to the horse, few dissimilarities exist among such species. In this chapter, we tried to highlight the anatomy, histology and physiology of the digestive system of domestic donkeys including tongue (mucosa, papillae, muscle, taste buds), teeth, pharynx, esophagus, stomach, saccus cecus, descending part, an ascending part and transversal part of the duodenum, jejunum, ileum, cecum, colon (right dorsal and ventral; left dorsal and ventral), rectum and anal canal. The microarchitecture of the tunica mucosa, next to the lumen, is focused upon. Morphology of the large accessary digestive glands viz. salivary gland, liver and pancreas were also highlighted. These structures are situated away from the gut-tubular system but are attached to its lumen through their specified duct system. Furthermore, peculiar microstructures of the internal layers, immune system and microbiome of the gut were correspondingly highlighted in the chapter.

**Keywords:** anatomy, histology, physiology, oral cavity, stomach, intestine, glands, microscope, donkey

#### **1. Introduction**

#### **1.1 Donkey in the past, present and future perspective**

Donkey (*Equus africanus asinus*) belongs to Equidae family like horse and is domesticated in most parts of the world [1]. The African wild ass living wildly has been declared as wild ancestor of today's donkey. The life span of donkeys is generally ranging from 25 to 50 years. It is known to have been used as a beast of burden. "The first findings of donkey came from ancient art and archeological records. Donkeys bred and produced mule's offspring which were used by the Spanish during their occupations and defeats. By the same time the donkeys got progressively significance in America and were used for shipping gold around

mountainous mines. Although the world has move toward the mechanization, but donkey (an ancient animal) is being used as biological vehicle and is known as beast of burden. In arid and semi-arid places, it serves man in carrying luggage and used for transportation purpose [2]. It can live on low quality high fiber diet and scarce amount of water. It can bear harsh climatic conditions. It is the source of bread and butter for the poor laborer of the developing country and is called the horse of poor man available in low price. It is the source of earning on daily bases for many poor families. Along with mules, donkeys are also used as a means of transportation by those armed forces who are deployed in the large mountainous areas [3]. Donkeys are used to guard sheep, as they are more inclined to stand and fight than to run from a predator. They provide a means of transportation for agricultural goods, building materials, droughts, tracking carts and riding humans themselves all over the world. Donkey is also named as and will remain an inexpensive horse [2]. It can go places where cars and other vehicles cannot go, so it can be used for transportation such as hilly areas [3]. In addition, Donkey milk is used as an alternative to human breast milk, as it has many of the same important qualities viz. low in fat contents, promotes healthy intestinal flora, have anti-inflammatory properties, contains immune enhancing compounds which protect the body against pathogen [4]. Donkey meat is eaten in many places of world. Italy is the largest consumer of donkey meat in Europe [5]. Donkey meat is considered tastier than horse meat and is a delicacy in most of the Chinese restaurants. Donkey meat burgers are a favored way of eating the meat and are eaten in Canada and Mexico for example. Donkey milk components are used in making cosmetics soaps and skin creams. Donkey is also used as test animal in pharmacokinetics [4]. Donkey hide gelatin (aka ass hides glue) is used in traditional Chinese medicine to treat bleeding dizziness insomnia and dry cough and a source of raw material for Shoes company. Donkeys also played role in reproduction and produced fertile or infertile mules which helped and used by humans for many purposes [2]. Based on loyal behavior, such animal holds a position as noticeable companions and guard of pet animals. Scientists of the advance countries like America are planning to use donkey in Artificial Intelligence by modifying its brain function and so it can be used in secret missions. Due to its importance, veterinarians and other researchers are interested in discovering further benefits out of it. Only a few studies highlighted and focused the anatomical and physiological aspects of the donkey alimentary system. Unlike other individuals, such animals are being offered low-cost fibers diet [1]. High fiber forage diets are better digested by donkeys than horses. Donkeys are said to possess a better digestive system than horses, it comprises of a series of tubular organs and associated glands [6]. Its function is to cut down the ingested complex food materials and converted into the valuable energy source and removing the wasted portion for maintaining the health and growth of the organism. The digestive system of the donkey is explored in detail in this chapter.

#### **2. Anatomy and physiology of the digestive system of donkey**

The donkey gut can be apportioned into two segments including the foregut made up of the stomach and small intestine and hindgut or large intestine is consists of cecum and colon. The overall digestive system is a hollow tube, starting with the mouth and oral cavity leading through to the anus with structures including the esophagus, stomach, small and large intestine, rectum and the anal canal in between [7]. The digestive glands like liver, pancreas and salivary glands are also

**169**

following formula:

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*)*

associated with the system. The entry of the gut (buccal cavity) is surrounded by the lips anteriorly and are present posterior to the nostrils, by the cheeks and teeth laterally, by the hard and soft palate dorsally, by the movable tongue ventrally which is present in the floor, and posteriorly it opens into the pharynx. The structures in the oral cavity include the tongue, teeth and gums, salivary glands, palates and

The lips are the main prehensile organ in donkeys, they are lined by stratified squamous keratinized epithelium and comprise of skin, glands, hair follicles, and tactile hairs. Microscopically lips are composed of epidermis, subcutaneous tissues thick layer of connective tissue, orbicularis oris muscle fibers (of skeletal type). The labial glands and a layer of adipose tissue are present in lamina propria and submucosa. The lips of donkey are mobile which help in collection and direction of grass toward the incisors for cutting and the premolar and molar teeth for

The equine tooth is made up of the same substances as human dentition i.e. cementum, enamel, dentine and pulp but the matrix is different, and our teeth are encapsulated in enamel whereas the donkey occlusal surface shows a cross section of all materials except pulp. Pulp is innermost layer contains vital structure like nerves, blood supply, lymphatics and bone forming cells the odontoblasts [9]. This soft structure is protected by outer layer. The next layer is which occupy main portion of the tooth but is less mineralized than enamel is the dentin. By this reason the dentin wears out more than enamel which is the hardest portion of the tooth. Enamel does not have ability to heal up if it is scratched and injured like the other tissue in tooth can, but it remains protected between cementum and dentin. Cementum is the outer layer and is similar to bone and assists connection between periodontal ligament and the tooth. This structure defends the tooth, maintaining it in the socket within the gum and provides care as the animal masticates. Only 11% of infundibula are completely cementum filled. The developing bone is externally lined by stratified squamous non keratinized epithelium followed by a primitive connective tissue. The incisors are located at the front of the mouth and are visible when you lift up the animal's lips [10]. The permanent incisors have crescent shaped depression called infundibulum that is filled with cementum. The incisors are used to cut the grass during grazing and also aid in assessing the animal age. Canine or bridal teeth are located between incisors and premolars. Lower canines are positioned more rostral than the upper ones. Male donkeys generally have four canines, but these generally do not fully develop in females. Wolf teeth are located just medial to first cheek teeth in both upper and lower jaws. They may be absent or four in number. Cheek teeth are most caudal group of teeth. Three molars and three premolars make up each row. Upper cheek teeth have infundibula that wear out with time. The molar are permanent teeth only. Based on closed location, collective premolars and molars performance is like a specific unit for the breakdown of food. Total number of equine teeth is as per the

Deciduous I3 C0 P3/I3 C0 P3 = 12 and the long − lasting are as 3 1 3(4) 3/3 1 3 3 = 20 (21) (1)

*DOI: http://dx.doi.org/10.5772/intechopen.92722*

immune tissues.

mastication [8].

**2.2 Dental anatomy in donkeys**

**2.1 Lips**

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*) DOI: http://dx.doi.org/10.5772/intechopen.92722*

associated with the system. The entry of the gut (buccal cavity) is surrounded by the lips anteriorly and are present posterior to the nostrils, by the cheeks and teeth laterally, by the hard and soft palate dorsally, by the movable tongue ventrally which is present in the floor, and posteriorly it opens into the pharynx. The structures in the oral cavity include the tongue, teeth and gums, salivary glands, palates and immune tissues.

#### **2.1 Lips**

*Equine Science*

mountainous mines. Although the world has move toward the mechanization, but donkey (an ancient animal) is being used as biological vehicle and is known as beast of burden. In arid and semi-arid places, it serves man in carrying luggage and used for transportation purpose [2]. It can live on low quality high fiber diet and scarce amount of water. It can bear harsh climatic conditions. It is the source of bread and butter for the poor laborer of the developing country and is called the horse of poor man available in low price. It is the source of earning on daily bases for many poor families. Along with mules, donkeys are also used as a means of transportation by those armed forces who are deployed in the large mountainous areas [3]. Donkeys are used to guard sheep, as they are more inclined to stand and fight than to run from a predator. They provide a means of transportation for agricultural goods, building materials, droughts, tracking carts and riding humans themselves all over the world. Donkey is also named as and will remain an inexpensive horse [2]. It can go places where cars and other vehicles cannot go, so it can be used for transportation such as hilly areas [3]. In addition, Donkey milk is used as an alternative to human breast milk, as it has many of the same important qualities viz. low in fat contents, promotes healthy intestinal flora, have anti-inflammatory properties, contains immune enhancing compounds which protect the body against pathogen [4]. Donkey meat is eaten in many places of world. Italy is the largest consumer of donkey meat in Europe [5]. Donkey meat is considered tastier than horse meat and is a delicacy in most of the Chinese restaurants. Donkey meat burgers are a favored way of eating the meat and are eaten in Canada and Mexico for example. Donkey milk components are used in making cosmetics soaps and skin creams. Donkey is also used as test animal in pharmacokinetics [4]. Donkey hide gelatin (aka ass hides glue) is used in traditional Chinese medicine to treat bleeding dizziness insomnia and dry cough and a source of raw material for Shoes company. Donkeys also played role in reproduction and produced fertile or infertile mules which helped and used by humans for many purposes [2]. Based on loyal behavior, such animal holds a position as noticeable companions and guard of pet animals. Scientists of the advance countries like America are planning to use donkey in Artificial Intelligence by modifying its brain function and so it can be used in secret missions. Due to its importance, veterinarians and other researchers are interested in discovering further benefits out of it. Only a few studies highlighted and focused the anatomical and physiological aspects of the donkey alimentary system. Unlike other individuals, such animals are being offered low-cost fibers diet [1]. High fiber forage diets are better digested by donkeys than horses. Donkeys are said to possess a better digestive system than horses, it comprises of a series of tubular organs and associated glands [6]. Its function is to cut down the ingested complex food materials and converted into the valuable energy source and removing the wasted portion for maintaining the health and growth of the organism. The digestive system of the

**168**

donkey is explored in detail in this chapter.

**2. Anatomy and physiology of the digestive system of donkey**

The donkey gut can be apportioned into two segments including the foregut made up of the stomach and small intestine and hindgut or large intestine is consists of cecum and colon. The overall digestive system is a hollow tube, starting with the mouth and oral cavity leading through to the anus with structures including the esophagus, stomach, small and large intestine, rectum and the anal canal in between [7]. The digestive glands like liver, pancreas and salivary glands are also

The lips are the main prehensile organ in donkeys, they are lined by stratified squamous keratinized epithelium and comprise of skin, glands, hair follicles, and tactile hairs. Microscopically lips are composed of epidermis, subcutaneous tissues thick layer of connective tissue, orbicularis oris muscle fibers (of skeletal type). The labial glands and a layer of adipose tissue are present in lamina propria and submucosa. The lips of donkey are mobile which help in collection and direction of grass toward the incisors for cutting and the premolar and molar teeth for mastication [8].

#### **2.2 Dental anatomy in donkeys**

The equine tooth is made up of the same substances as human dentition i.e. cementum, enamel, dentine and pulp but the matrix is different, and our teeth are encapsulated in enamel whereas the donkey occlusal surface shows a cross section of all materials except pulp. Pulp is innermost layer contains vital structure like nerves, blood supply, lymphatics and bone forming cells the odontoblasts [9]. This soft structure is protected by outer layer. The next layer is which occupy main portion of the tooth but is less mineralized than enamel is the dentin. By this reason the dentin wears out more than enamel which is the hardest portion of the tooth. Enamel does not have ability to heal up if it is scratched and injured like the other tissue in tooth can, but it remains protected between cementum and dentin. Cementum is the outer layer and is similar to bone and assists connection between periodontal ligament and the tooth. This structure defends the tooth, maintaining it in the socket within the gum and provides care as the animal masticates. Only 11% of infundibula are completely cementum filled. The developing bone is externally lined by stratified squamous non keratinized epithelium followed by a primitive connective tissue. The incisors are located at the front of the mouth and are visible when you lift up the animal's lips [10]. The permanent incisors have crescent shaped depression called infundibulum that is filled with cementum. The incisors are used to cut the grass during grazing and also aid in assessing the animal age. Canine or bridal teeth are located between incisors and premolars. Lower canines are positioned more rostral than the upper ones. Male donkeys generally have four canines, but these generally do not fully develop in females. Wolf teeth are located just medial to first cheek teeth in both upper and lower jaws. They may be absent or four in number. Cheek teeth are most caudal group of teeth. Three molars and three premolars make up each row. Upper cheek teeth have infundibula that wear out with time. The molar are permanent teeth only. Based on closed location, collective premolars and molars performance is like a specific unit for the breakdown of food. Total number of equine teeth is as per the following formula:

Deciduous I3 C0 P3/I3 C0 P3 = 12 and the long − lasting are as 3 1 3(4) 3/3 1 3 3 = 20 (21) (1)

The deciduous incisor teeth are rounded at the top and are whiter in color while the long-lasting are adopting square shape at the margin of the gum and appears yellower. Teeth eruption processes are as follows.


#### **2.3 Donkey tongue**

It is a strong muscular organ enclosed in thick mucosa. It is very sensitive organ with a groove between inner part of it which is connected to underlying tissue and a free part in front. This organ has spatula shaped having torus linguae (extended torus and muscular distinction), which is distinctive for Equidae. Stratified squamous keratinized epithelium lining the external surface followed by connective tissue and a layer of skeletal muscles [11]. The muscle layers are arranged in various forms which help in rotation of the tongue during feed mastication. Epithelium lining ventrally is the non-cornified. Filiform, fungiform, foliate and vallate papillae are present at three parts of tongue (apex, body, and base). All types of papillae are lined by partial to complete carnified epithelium. Filiform papillae are mechanical and almost cover major portion on the dorsal surface. It is short and thin at apex, pointed and rough at body, and elongated at the caudal portion. Fungiform mainly scattered at lateral surfaces, around the filiform and are round to lobulated. These are larger, wider, taller but less in number than filiform. The vallate papillae with circular grove and central spherical bulges are positioned caudally in the body and 3–4 times larger than fungiform. Group of foliate are located near the base of palato-glossal arch and are organized like leaves alienated by variable grooves. Fungiform and filiform are devoid of taste buds but vallate and foliate has taste buds. Basal cells are present at the base of each taste bud and act like the stem cells. As compared to the tongue of horses, the feature is the occasional occurrence of the dorsum cartilage (cartilago dorsi linguae) of the tongue. Lymphatic nodules are special aggregated lymphoid cells and are present dorsally. Small mucous secreting labial glands are also present in connective tissue, secretion of which moistens the oral mucosa. The connective tissue in the lamina propria is richly supplied with blood vessels, lymphatics, nerves and adipose tissue.

#### **2.4 Cheek of donkey**

The structure of the cheek is like that of lips, designed principally of buccinator muscles and contains some minor glands (salivary). The powerful muscles of cheek help in mastication, grinding and mixing of food. These includes masseter, pterygoid medially, pterygoid laterally [12]. These muscles get their nerve innervation from the mandibular branch of the trigeminal nerve. Furthermore, cheek muscles involved in closing the mouth through elevation of the mandible [13].

#### *2.4.1 Masseter muscles*

These muscles have wide multipennate muscles with numerous tendinous connections. In the donkey, it is the largest muscle involved in mastication. It is grouped into; "Proper (first, second superficial, middle and deep) masseter

**171**

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*)*

which supply blood to the masseter muscle defined its importance.

coatings and improper masseter muscles groups (zygomatico-mandibularis and maxillo-mandibularis)". Its main function comprises of the movement for chewing, achieved by the masseter group (proper) and definite shutting of the oral cavity is executed by the improper type of masseter group [14]. The improper muscle moves the mandible in lever style. Arteries of masseter muscle include masseteric artery, transverse facial artery, buccal artery, facial artery. The arrangement of the vessels

These muscles routed through the bottom of the skull via mandible medially. Pterygoid muscles accompany the masseter during function. Upon bilateral contraction the pterygoid muscles caused elevation of the mandible and upon performing unilateral action they attract the mandible sidewise of the contracting muscle [13]. Its lateral portion is capable to direct the rostral direction of the mandible,

The temporal muscle is originated from the temporal crest and occupies the temporal fossa. It is inserted on the coronoid process of the mandible. Its functions include elevations of the mandible and help other muscles mutually during masti-

These caudle and rostral bellied muscles are not the actual muscle of mastication but may also add partially to the jaw movements during opening to the oral cavity. It prolongs among the process of paracondylar of the occiput and the mandible medially [13]. The facial nerve innervates the caudal part while the mandibular nerve innervated the rostral part. The lateral portion is formed from the extension of the caudal belly, attached on the mandibular angle and attracts the mandible bone backward. Below the basihyoid bone it develops the rostral belly, which attaches medially to the mandible body. This muscle opens the oral cavity by pushing the

The palate has mucosa on both oral and nasal sides and has soft and hard parts.

Pharynx is about 15 cm in an adult animal. It is present at the back (posterior) of the mouth and is located between the skull at base and the initial two cervical vertebrae at dorsal portion and ventrally the larynx. On lateral side, two pairs of palatopharyngeal arches are present from the soft palate to esophagus. Wall of

Oral mucosa is lined by tough cornified squamous epithelium. Hard palate is formed by union of palatine, maxillary, and incisive bones with no muscles [13]. Soft palate is a muscular structure made of intrinsic paired palatine muscles paired extrinsic tensor and levator veli palatine muscles along with palatine glands present in it. Trigeminal nerve supply to the palate and glosso-pharyngeal and vagus nerve supply the muscles of soft palate. Lymphoid follicles are present in the lamina

*DOI: http://dx.doi.org/10.5772/intechopen.92722*

particularly when the oral cavity is opened.

*2.4.2 Pterygoid muscles*

*2.4.3 Temporal muscle*

*2.4.4 Digastric muscle*

cation's [13].

mandible [11].

propria along with FCT [14].

**2.6 Pharynx of donkey**

**2.5 Palate**

#### *Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*) DOI: http://dx.doi.org/10.5772/intechopen.92722*

coatings and improper masseter muscles groups (zygomatico-mandibularis and maxillo-mandibularis)". Its main function comprises of the movement for chewing, achieved by the masseter group (proper) and definite shutting of the oral cavity is executed by the improper type of masseter group [14]. The improper muscle moves the mandible in lever style. Arteries of masseter muscle include masseteric artery, transverse facial artery, buccal artery, facial artery. The arrangement of the vessels which supply blood to the masseter muscle defined its importance.

#### *2.4.2 Pterygoid muscles*

*Equine Science*

**2.3 Donkey tongue**

**2.4 Cheek of donkey**

*2.4.1 Masseter muscles*

The deciduous incisor teeth are rounded at the top and are whiter in color while the long-lasting are adopting square shape at the margin of the gum and appears

**Teeth Date of deciduous teeth eruption Date of permanent teeth eruption (years)**

It is a strong muscular organ enclosed in thick mucosa. It is very sensitive organ with a groove between inner part of it which is connected to underlying tissue and a free part in front. This organ has spatula shaped having torus linguae (extended torus and muscular distinction), which is distinctive for Equidae. Stratified squamous keratinized epithelium lining the external surface followed by connective tissue and a layer of skeletal muscles [11]. The muscle layers are arranged in various forms which help in rotation of the tongue during feed mastication. Epithelium lining ventrally is the non-cornified. Filiform, fungiform, foliate and vallate papillae are present at three parts of tongue (apex, body, and base). All types of papillae are lined by partial to complete carnified epithelium. Filiform papillae are mechanical and almost cover major portion on the dorsal surface. It is short and thin at apex, pointed and rough at body, and elongated at the caudal portion. Fungiform mainly scattered at lateral surfaces, around the filiform and are round to lobulated. These are larger, wider, taller but less in number than filiform. The vallate papillae with circular grove and central spherical bulges are positioned caudally in the body and 3–4 times larger than fungiform. Group of foliate are located near the base of palato-glossal arch and are organized like leaves alienated by variable grooves. Fungiform and filiform are devoid of taste buds but vallate and foliate has taste buds. Basal cells are present at the base of each taste bud and act like the stem cells. As compared to the tongue of horses, the feature is the occasional occurrence of the dorsum cartilage (cartilago dorsi linguae) of the tongue. Lymphatic nodules are special aggregated lymphoid cells and are present dorsally. Small mucous secreting labial glands are also present in connective tissue, secretion of which moistens the oral mucosa. The connective tissue in the lamina propria is richly supplied with

The structure of the cheek is like that of lips, designed principally of buccinator muscles and contains some minor glands (salivary). The powerful muscles of cheek help in mastication, grinding and mixing of food. These includes masseter, pterygoid medially, pterygoid laterally [12]. These muscles get their nerve innervation from the mandibular branch of the trigeminal nerve. Furthermore, cheek muscles

involved in closing the mouth through elevation of the mandible [13].

These muscles have wide multipennate muscles with numerous tendinous connections. In the donkey, it is the largest muscle involved in mastication. It is grouped into; "Proper (first, second superficial, middle and deep) masseter

Central incisors 0–2 weeks 3–3.5 Middle incisors 5–8 weeks 4 Corner incisors 1 year 5–5.5

yellower. Teeth eruption processes are as follows.

blood vessels, lymphatics, nerves and adipose tissue.

**170**

These muscles routed through the bottom of the skull via mandible medially. Pterygoid muscles accompany the masseter during function. Upon bilateral contraction the pterygoid muscles caused elevation of the mandible and upon performing unilateral action they attract the mandible sidewise of the contracting muscle [13]. Its lateral portion is capable to direct the rostral direction of the mandible, particularly when the oral cavity is opened.

#### *2.4.3 Temporal muscle*

The temporal muscle is originated from the temporal crest and occupies the temporal fossa. It is inserted on the coronoid process of the mandible. Its functions include elevations of the mandible and help other muscles mutually during mastication's [13].

#### *2.4.4 Digastric muscle*

These caudle and rostral bellied muscles are not the actual muscle of mastication but may also add partially to the jaw movements during opening to the oral cavity. It prolongs among the process of paracondylar of the occiput and the mandible medially [13]. The facial nerve innervates the caudal part while the mandibular nerve innervated the rostral part. The lateral portion is formed from the extension of the caudal belly, attached on the mandibular angle and attracts the mandible bone backward. Below the basihyoid bone it develops the rostral belly, which attaches medially to the mandible body. This muscle opens the oral cavity by pushing the mandible [11].

#### **2.5 Palate**

The palate has mucosa on both oral and nasal sides and has soft and hard parts. Oral mucosa is lined by tough cornified squamous epithelium. Hard palate is formed by union of palatine, maxillary, and incisive bones with no muscles [13]. Soft palate is a muscular structure made of intrinsic paired palatine muscles paired extrinsic tensor and levator veli palatine muscles along with palatine glands present in it. Trigeminal nerve supply to the palate and glosso-pharyngeal and vagus nerve supply the muscles of soft palate. Lymphoid follicles are present in the lamina propria along with FCT [14].

#### **2.6 Pharynx of donkey**

Pharynx is about 15 cm in an adult animal. It is present at the back (posterior) of the mouth and is located between the skull at base and the initial two cervical vertebrae at dorsal portion and ventrally the larynx. On lateral side, two pairs of palatopharyngeal arches are present from the soft palate to esophagus. Wall of

pharynx consist of striated muscles. It includes the nasopharynx which is entrance to auditory tubes, oropharynx and laryngopharynx [15]. Nasopharyngeal mucosal epithelium is composed of pseudostratified columnar epithelium with goblet cells. Lymphoid follicles can also be seen in the lamina propria and submucosal area. Nasopharynx is innervated by cranial nerves V, IX, X, XII. It is also composed of sensory receptors of glossopharyngeal and trigeminal nerves. During swallowing, the soft palate is raised which divides pharynx into dorsal and ventral sections [13]. It plays important role in deglutition. It serves as pathway of food from mouth to esophagus. It consists of rostral constrictor muscles including the hypopharyngeal, pterygoid, and palatopharyngeus. The stylopharyngeus are the muscles responsible to dilate the area while pterygopharyngeal muscle and palatopharyngeal muscles shorten the pharynx. Palatopharyngeal muscles also close the pharyngeal arch. There are some tactile receptors which detected the air flow and cause dilatation of the air way by stimulating the gag reflex. Augmented action of such receptors stabilizing the muscles which improves the dilatation of upper respiratory tract and prevent it from being collapsed. It is advised that glossopharyngeal nerves should never locally anesthetized otherwise there be dysfunction of oropharyngeal muscle which may causing collapse of dorsal nasopharynx and ultimately inspiratory obstruction in exercising donkey. Failure of pharynx or neuromuscular activities will result into the severe respiratory disorders.

#### **2.7 Tonsils**

This tissue is responsible for defense, located at the rare area of the throat. A tissue of soft lymphoid follicle like the lymph nodes surrounded by a layer of stratified squamous epithelium. The mucosa invaginates deep in the lamina propria forming crypts and fundi [11]. Both defuse and nodular arrangements of the lymphoid tissues are present.

#### **2.8 Esophagus**

The length of the esophagus depends upon the body of animal. It consists of cervical, thoracic and abdominal parts. It moves lateral to trachea as moving down and becomes ventral again at thoracic inlet. Unique feature of donkey esophagus is its pigmentation at different parts. Esophageal obstruction is also common in donkey due to different anatomical entrance to stomach [16]. Cervical part of the esophagus is located dorsal to trachea and ventral to cervical vertebrae and the thoracic part is located dorsal to sternum, medially in the thoracic cavity. The esophagus ranges from 125 to 200 cm in length in average adult animal. It lies dorsally on trachea in the cranial third then turned toward left in the middle third of the neck [17]. In the area of thoracic inlet, it lies ventrally to the trachea. Under microscope its wall is divided into mucosa, submucosa, muscularis and tunica adventitia. Mucosa is the innermost part of the esophagus toward lumen and is lined by keratinized stratified squamous epithelium. In the lamina propria, the glands are present along with a layer of FCT and some lymphoid follicles, blood vessels and other vasculature. Lower layer of the mucosa is surrounded by smooth muscle called muscularis mucosae. The submucosa contains elastic fibers, adipose tissue and seromucous gland. The muscularis externa is composed of skeletal muscle in the proximal twothirds and turns to smooth muscle in the distal third. The skeletal muscle layers are adapted in inner circular and outer longitudinal arrangements. The cervical pleura and peritoneum add to tunica adventitia in all portions of the esophagus. The loose attachments of the esophagus with the adjacent tissue permit the neck movement during swallowing. At abdominal portion the esophagus has a serosal covering.

**173**

then goes to caecum and colon for microbial digestion.

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*)*

The function of esophagus is to provide pathway to partially digested food into the

Lower portion of the esophagus and the stomach lies toward right side in the abdominal cavity. Between esophagus and stomach there occurs a junction i.e., esophagus-gastric junction [17]. The stomach has three sections, saccus caecus, fundic and pyloric regions. The saccus caecus is a non-glandular portion on stomach and is located close to the esophagus entrance in the stomach [16]. It is situated ventrally to the diaphragmatic left crust and is underneath the dorsal portion of 16th and 17th ribs. It relates to pancreas, present behind the great colon extinction and situated laterally to spleen bases. This portion is covered by keratinized stratified squamous epithelium. The keratin layer thickness differs with degree of stomach distension, age and diet of the animal. The lamina propria normally has plasma cells, lymphocytes, mast cells and neutrophils. The muscularis mucosa is continuous and the submucosa hold nerves plexus and lymphatics. The muscularis externa is comprised smooth muscle arranged in three layers viz. oblique (inner), circular (middle) and longitudinal (outer) layers. Between the inner circular and outer longitudinal layers of muscle there is the myenteric nerve plexus. In this area the HCL initially combine with the ingested food mass and reduces the prior process of fermentation that initiated with the discharge of sugars (soluble) from the food in donkey's oral cavity. It is imperative that in the stomach the fermentation is very sparse because it leads to the gas formation. In donkey there is a slight experience to belch or otherwise to dispel collecting gas. Histologically, the lining epithelium at junction of stomach is abruptly transit to columnar epithelium from stratified squamous form. This junction acts like a valve that does not allow acidic contents of stomach to enter in esophagus. Due to any abnormality, this junction is not performing its proper function; it can result in reflux esophagitis. Externally diaphragmatic crura and internally C-shaped sling fibers of stomach make it possible to perform its pinchcock like action. Grossly we can say that proximal cardiac portion of stomach and distal end of esophagus makes this muscular junction. The stomach of donkey is like horses in its conformation. The average weight of an empty stomach in donkey is 1.5 kg. The comparative stomach capacity of donkey is 14 and the caecum and colon is about 80, whereas ruminants have the stomach capacity around 80 and that of caecum and colon is only 13. Hence the stomach of donkey and caecum of large ruminants are similar. Donkeys have monogastric type of small stomach that bounds the feed portion which can be got at a time. It attempts incessant foraging as numerous slight feedings are superior than few big meals since the stomach starts to unfilled when it is 2/3 full irrespective the food is processed or not in the stomach. The mucosa has folds which flattened when the stomach fills and has gastric pits and glands. The cardiac glandular region of the stomach has short, coiled tubular glands that are lined by simple cuboidal epithelium. Proper gastric (fundic) regions of the stomach is containing straight, branched tubular glands of which narrow neck, long body and dilated blind ended fundus [19]. The pyloric region has deeper pits. The mucosal glands are lined by the chief (zymogen secreting) and parietal cells (acid secretion) along with mucous neck cells. The chief cells are larger in number while the parietal cells are larger in size. Although the digestion by microbial happens in caecum and colon in donkeys while stomach temporarily stores food because of its emptying behavior. Overall compared to other animals, larger area of the donkey's stomach is covered by the non-glandular regions [20]. A small amount of food is digested in the stomach and

*DOI: http://dx.doi.org/10.5772/intechopen.92722*

**2.9 Stomach**

stomach. There is no digestion in esophagus [18].

The function of esophagus is to provide pathway to partially digested food into the stomach. There is no digestion in esophagus [18].

#### **2.9 Stomach**

*Equine Science*

**2.7 Tonsils**

are present.

**2.8 Esophagus**

pharynx consist of striated muscles. It includes the nasopharynx which is entrance to auditory tubes, oropharynx and laryngopharynx [15]. Nasopharyngeal mucosal epithelium is composed of pseudostratified columnar epithelium with goblet cells. Lymphoid follicles can also be seen in the lamina propria and submucosal area. Nasopharynx is innervated by cranial nerves V, IX, X, XII. It is also composed of sensory receptors of glossopharyngeal and trigeminal nerves. During swallowing, the soft palate is raised which divides pharynx into dorsal and ventral sections [13]. It plays important role in deglutition. It serves as pathway of food from mouth to esophagus. It consists of rostral constrictor muscles including the hypopharyngeal, pterygoid, and palatopharyngeus. The stylopharyngeus are the muscles responsible to dilate the area while pterygopharyngeal muscle and palatopharyngeal muscles shorten the pharynx. Palatopharyngeal muscles also close the pharyngeal arch. There are some tactile receptors which detected the air flow and cause dilatation of the air way by stimulating the gag reflex. Augmented action of such receptors stabilizing the muscles which improves the dilatation of upper respiratory tract and prevent it from being collapsed. It is advised that glossopharyngeal nerves should never locally anesthetized otherwise there be dysfunction of oropharyngeal muscle which may causing collapse of dorsal nasopharynx and ultimately inspiratory obstruction in exercising donkey. Failure of pharynx or neuromuscular activities

This tissue is responsible for defense, located at the rare area of the throat. A tissue

The length of the esophagus depends upon the body of animal. It consists of cervical, thoracic and abdominal parts. It moves lateral to trachea as moving down and becomes ventral again at thoracic inlet. Unique feature of donkey esophagus is its pigmentation at different parts. Esophageal obstruction is also common in donkey due to different anatomical entrance to stomach [16]. Cervical part of the esophagus is located dorsal to trachea and ventral to cervical vertebrae and the thoracic part is located dorsal to sternum, medially in the thoracic cavity. The esophagus ranges from 125 to 200 cm in length in average adult animal. It lies dorsally on trachea in the cranial third then turned toward left in the middle third of the neck [17]. In the area of thoracic inlet, it lies ventrally to the trachea. Under microscope its wall is divided into mucosa, submucosa, muscularis and tunica adventitia. Mucosa is the innermost part of the esophagus toward lumen and is lined by keratinized stratified squamous epithelium. In the lamina propria, the glands are present along with a layer of FCT and some lymphoid follicles, blood vessels and other vasculature. Lower layer of the mucosa is surrounded by smooth muscle called muscularis mucosae. The submucosa contains elastic fibers, adipose tissue and seromucous gland. The muscularis externa is composed of skeletal muscle in the proximal twothirds and turns to smooth muscle in the distal third. The skeletal muscle layers are adapted in inner circular and outer longitudinal arrangements. The cervical pleura and peritoneum add to tunica adventitia in all portions of the esophagus. The loose attachments of the esophagus with the adjacent tissue permit the neck movement during swallowing. At abdominal portion the esophagus has a serosal covering.

of soft lymphoid follicle like the lymph nodes surrounded by a layer of stratified squamous epithelium. The mucosa invaginates deep in the lamina propria forming crypts and fundi [11]. Both defuse and nodular arrangements of the lymphoid tissues

will result into the severe respiratory disorders.

**172**

Lower portion of the esophagus and the stomach lies toward right side in the abdominal cavity. Between esophagus and stomach there occurs a junction i.e., esophagus-gastric junction [17]. The stomach has three sections, saccus caecus, fundic and pyloric regions. The saccus caecus is a non-glandular portion on stomach and is located close to the esophagus entrance in the stomach [16]. It is situated ventrally to the diaphragmatic left crust and is underneath the dorsal portion of 16th and 17th ribs. It relates to pancreas, present behind the great colon extinction and situated laterally to spleen bases. This portion is covered by keratinized stratified squamous epithelium. The keratin layer thickness differs with degree of stomach distension, age and diet of the animal. The lamina propria normally has plasma cells, lymphocytes, mast cells and neutrophils. The muscularis mucosa is continuous and the submucosa hold nerves plexus and lymphatics. The muscularis externa is comprised smooth muscle arranged in three layers viz. oblique (inner), circular (middle) and longitudinal (outer) layers. Between the inner circular and outer longitudinal layers of muscle there is the myenteric nerve plexus. In this area the HCL initially combine with the ingested food mass and reduces the prior process of fermentation that initiated with the discharge of sugars (soluble) from the food in donkey's oral cavity. It is imperative that in the stomach the fermentation is very sparse because it leads to the gas formation. In donkey there is a slight experience to belch or otherwise to dispel collecting gas. Histologically, the lining epithelium at junction of stomach is abruptly transit to columnar epithelium from stratified squamous form. This junction acts like a valve that does not allow acidic contents of stomach to enter in esophagus. Due to any abnormality, this junction is not performing its proper function; it can result in reflux esophagitis. Externally diaphragmatic crura and internally C-shaped sling fibers of stomach make it possible to perform its pinchcock like action. Grossly we can say that proximal cardiac portion of stomach and distal end of esophagus makes this muscular junction. The stomach of donkey is like horses in its conformation. The average weight of an empty stomach in donkey is 1.5 kg. The comparative stomach capacity of donkey is 14 and the caecum and colon is about 80, whereas ruminants have the stomach capacity around 80 and that of caecum and colon is only 13. Hence the stomach of donkey and caecum of large ruminants are similar. Donkeys have monogastric type of small stomach that bounds the feed portion which can be got at a time. It attempts incessant foraging as numerous slight feedings are superior than few big meals since the stomach starts to unfilled when it is 2/3 full irrespective the food is processed or not in the stomach. The mucosa has folds which flattened when the stomach fills and has gastric pits and glands. The cardiac glandular region of the stomach has short, coiled tubular glands that are lined by simple cuboidal epithelium. Proper gastric (fundic) regions of the stomach is containing straight, branched tubular glands of which narrow neck, long body and dilated blind ended fundus [19]. The pyloric region has deeper pits. The mucosal glands are lined by the chief (zymogen secreting) and parietal cells (acid secretion) along with mucous neck cells. The chief cells are larger in number while the parietal cells are larger in size. Although the digestion by microbial happens in caecum and colon in donkeys while stomach temporarily stores food because of its emptying behavior. Overall compared to other animals, larger area of the donkey's stomach is covered by the non-glandular regions [20]. A small amount of food is digested in the stomach and then goes to caecum and colon for microbial digestion.

#### **2.10 Intestine**

It is positioned ventral to the vertebral column in the abdominal cavity and has the following three parts. The duodenum is the initial and shortest portion of the small intestine located at left side of the abdominal cavity [17]. Duodenum joins the jejunum and the stomach together and is divided into the following four parts:

1.Superior (first) part also called ampulla duodeni


Superior part of duodenum: It is in interaction with the liver through the visceral surface and forming ampulla which is a dilated portion and a sigmoid flexure. The initial curve of the flexure is dorsally convex and the other also called cranial flexure is ventrally convex which provide the site of attachment for body of the pancreas. The first 2 cm of superior part of duodenum, immediately distal to the pylorus has mesentery and is mobile. This free part called the ampulla (duodenal cap). The distal 3 cm of the superior part have no mesentery and are immobile because they are retroperitoneal. The duodenal superior segment ascends from pylorus and is overlapped by the liver. Peritoneum covers its anterior aspects, but it is bare of peritoneum posteriorly, except for the ampulla.

The major duodenal papilla is a rounded projection at the beginning portion of the mutual pancreatic and bile duct into the duodenum and is the primary source of bile and other enzymes secretion that ease the process of digestion. Mucosa forming protruding papillary folds at ampulla where the lining epithelium transitions from common gut surface type to pancreatobiliary type like distal ducts. The lamina propria mucosa contains infrequent plasma cells, lymphocytes and mast cells. Little ductless mucous glands ductules lie beneath the mucosa. Sphincter of Oddi represented by smooth muscles possibly ranged into mucosal surface folds and might have some neighboring acini (pancreatic), but typically the islets are not seen nearby major papillae. The development of major duodenal papilla begins with evaginations of the gut tube lies caudal to the stomach. The dorsal mesogastrium and the ventral mesogastrium pancreatic buds are formed. Few of the epithelium fail their associations to the emerging pancreatic duct system and lead to develop into the endocrine portion in the form of islets of Langerhans in pancreas. The minor papilla (duodenal) is positioned typically about 2 cm ventroproximal to the major duodenal papilla. Jejunum is the longest portion in the small intestine. It is situated in the middle part of the intestine [21] and is present in abdominal left side. A large number of digestive glands are present in the jejunum responsible for releasing buffers and enzymes into the gut lumen. In this largest luminal absorptive area, most of minerals and nutrients are absorbed [22]. Ilium is the last part of the small intestine and is present also in the abdominal left side and is the final section of small intestine. The ileocecal fold is situated between the antimesenteric side of the ileum and the tenia dorsalis of the cecum. Its role is to absorb all the remaining bile salts vitamin B12, and other digested stuffs that were available un-absorbed in the lumen. Ileal and cecocolic ostia generally have a small opening or orifice. A muscular layer circular in shape is the sphincter which is connection of the ileum and the cecum called ileal ostium (ileocecal valve). During dissection of the gastrointestinal tract of donkey, these are the macroscopic structures. In the terminal portion

**175**

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*)*

of the gastrointestinal tract (GIT) at the cecal basis, the ostia (ileo-ceco-colic) are detected undoubtedly [23]. The ileal ostia inhibit the large intestinal luminal contents (rich in bacteria) refluxes back to the small intestine. The Peyer's patches located at the ileal submucosal tunics are the distinguishing histological items [24]. The ileocecal and cecocolic folds (peritoneal) set the cecum with other intestinal portions. Through the *ceco-colic ostium* the substances present in the ceca are drained directly into the colon (ventral). Gas accompanied ingesta are also eliminated across this ostium. Mucosa of the small intestine is lined by simple columnar epithelium. It covers the longest villi and the highest number of Goblet cells related to other parts of small intestine [22]. Sub-mucosa of duodenum contains Brunner's gland that secrete a serous secretion. Two layers, circular (inner) and longitudinal (outer) arrangements of muscularis externa and the outer serosa is present in its wall. The cecum is a portion of large intestine having pouch-like region present in pelvic portion of abdominal cavity located laterally and inferior to the ileum [17]. It is a very large chamber. The cecum has comparatively thicker mucosa, lined by simple absorptive columnar epithelium having plentiful goblet cells and enteroendocrine cells. Its lamina propria and muscular mucosae is identical to that of small intestine and the glands are packed tightly and lengthier. They lack Paneth cells. The cecum further absorbed the salt and remaining digested fluids through its thick mucosa and also add mucous to the remaining intra luminal contents [20]. The colon is present in abdominal cavity [17] and pushes all other organs cranially to thoracic part of abdominal cavity. The hindgut of the equine keeps similar job to that of other animals' large intestine viz. retention, further mixing and forward movement of the intraluminal contents. Such cecal movement is based on forced

Lamina propria lymphocytes are B-cells that secrete IgA (Antibody A). IgA comes into lumen through epithelial cells; here it performs the function of adhesion and invasion of bacteria. Intraepithelial lymphocytes are present in the basolateral spaces between luminal epithelial cells [25]. Microfold cell (M-cell) is present in mucosa-associated lymphoid tissues [26]. Its main objective is to conveyance luminal antigen to the cellular immune system. Intestinal macrophages are heterogeneous and have the ability to locate and engulf bacteria [24], virus, fungi and parasites. Intestinal macrophages are mainly located in sub-epithelial area. Activated macrophages are important source of cytokines (IL-10). These prevents large intestine from excessive inflammation during bacterial infections. Paneth cells are present just beneath the intestinal stem in intestinal gland (crypts) in colon. These cells produce great amount of alpha defensins and other antimicrobial

The ascending colon is splatted into left dorsal, left ventral, right dorsal and right ventral portions by the flexures (sternal flexure, pelvic and diaphragmatic). Location of the sternal flexure linking to the pair portions of the ventral colon [18]. In the border between dorsal and ventral colon the pelvic flexure is located, and the diaphragmatic flexure location is between the pair portions of dorsal colon. The ascending mesocolon is attached with ventral and dorsal parts. Ventral and dorsal colon is similar in length and is a part of the gastrointestinal tract of donkey. The transverse colon is positioned between the descending and ascending colon. The

peptides such as secretory phospholipase A2 and lysozymes.

descending colon has extended mesocolon (descending).

*DOI: http://dx.doi.org/10.5772/intechopen.92722*

contractions of the wall.

**2.12 Colon of donkey**

**2.11 Immune cells of the intestine**

#### *Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*) DOI: http://dx.doi.org/10.5772/intechopen.92722*

of the gastrointestinal tract (GIT) at the cecal basis, the ostia (ileo-ceco-colic) are detected undoubtedly [23]. The ileal ostia inhibit the large intestinal luminal contents (rich in bacteria) refluxes back to the small intestine. The Peyer's patches located at the ileal submucosal tunics are the distinguishing histological items [24]. The ileocecal and cecocolic folds (peritoneal) set the cecum with other intestinal portions. Through the *ceco-colic ostium* the substances present in the ceca are drained directly into the colon (ventral). Gas accompanied ingesta are also eliminated across this ostium. Mucosa of the small intestine is lined by simple columnar epithelium. It covers the longest villi and the highest number of Goblet cells related to other parts of small intestine [22]. Sub-mucosa of duodenum contains Brunner's gland that secrete a serous secretion. Two layers, circular (inner) and longitudinal (outer) arrangements of muscularis externa and the outer serosa is present in its wall. The cecum is a portion of large intestine having pouch-like region present in pelvic portion of abdominal cavity located laterally and inferior to the ileum [17]. It is a very large chamber. The cecum has comparatively thicker mucosa, lined by simple absorptive columnar epithelium having plentiful goblet cells and enteroendocrine cells. Its lamina propria and muscular mucosae is identical to that of small intestine and the glands are packed tightly and lengthier. They lack Paneth cells. The cecum further absorbed the salt and remaining digested fluids through its thick mucosa and also add mucous to the remaining intra luminal contents [20]. The colon is present in abdominal cavity [17] and pushes all other organs cranially to thoracic part of abdominal cavity. The hindgut of the equine keeps similar job to that of other animals' large intestine viz. retention, further mixing and forward movement of the intraluminal contents. Such cecal movement is based on forced contractions of the wall.

#### **2.11 Immune cells of the intestine**

Lamina propria lymphocytes are B-cells that secrete IgA (Antibody A). IgA comes into lumen through epithelial cells; here it performs the function of adhesion and invasion of bacteria. Intraepithelial lymphocytes are present in the basolateral spaces between luminal epithelial cells [25]. Microfold cell (M-cell) is present in mucosa-associated lymphoid tissues [26]. Its main objective is to conveyance luminal antigen to the cellular immune system. Intestinal macrophages are heterogeneous and have the ability to locate and engulf bacteria [24], virus, fungi and parasites. Intestinal macrophages are mainly located in sub-epithelial area. Activated macrophages are important source of cytokines (IL-10). These prevents large intestine from excessive inflammation during bacterial infections. Paneth cells are present just beneath the intestinal stem in intestinal gland (crypts) in colon. These cells produce great amount of alpha defensins and other antimicrobial peptides such as secretory phospholipase A2 and lysozymes.

#### **2.12 Colon of donkey**

The ascending colon is splatted into left dorsal, left ventral, right dorsal and right ventral portions by the flexures (sternal flexure, pelvic and diaphragmatic). Location of the sternal flexure linking to the pair portions of the ventral colon [18]. In the border between dorsal and ventral colon the pelvic flexure is located, and the diaphragmatic flexure location is between the pair portions of dorsal colon. The ascending mesocolon is attached with ventral and dorsal parts. Ventral and dorsal colon is similar in length and is a part of the gastrointestinal tract of donkey. The transverse colon is positioned between the descending and ascending colon. The descending colon has extended mesocolon (descending).

*Equine Science*

**2.10 Intestine**

It is positioned ventral to the vertebral column in the abdominal cavity and has the following three parts. The duodenum is the initial and shortest portion of the small intestine located at left side of the abdominal cavity [17]. Duodenum joins the jejunum and the stomach together and is divided into the following four parts:

Superior part of duodenum: It is in interaction with the liver through the visceral

The major duodenal papilla is a rounded projection at the beginning portion of the mutual pancreatic and bile duct into the duodenum and is the primary source of bile and other enzymes secretion that ease the process of digestion. Mucosa forming protruding papillary folds at ampulla where the lining epithelium transitions from common gut surface type to pancreatobiliary type like distal ducts. The lamina propria mucosa contains infrequent plasma cells, lymphocytes and mast cells. Little ductless mucous glands ductules lie beneath the mucosa. Sphincter of Oddi represented by smooth muscles possibly ranged into mucosal surface folds and might have some neighboring acini (pancreatic), but typically the islets are not seen nearby major papillae. The development of major duodenal papilla begins with evaginations of the gut tube lies caudal to the stomach. The dorsal mesogastrium and the ventral mesogastrium pancreatic buds are formed. Few of the epithelium fail their associations to the emerging pancreatic duct system and lead to develop into the endocrine portion in the form of islets of Langerhans in pancreas. The minor papilla (duodenal) is positioned typically about 2 cm ventroproximal to the major duodenal papilla. Jejunum is the longest portion in the small intestine. It is situated in the middle part of the intestine [21] and is present in abdominal left side. A large number of digestive glands are present in the jejunum responsible for releasing buffers and enzymes into the gut lumen. In this largest luminal absorptive area, most of minerals and nutrients are absorbed [22]. Ilium is the last part of the small intestine and is present also in the abdominal left side and is the final section of small intestine. The ileocecal fold is situated between the antimesenteric side of the ileum and the tenia dorsalis of the cecum. Its role is to absorb all the remaining bile salts vitamin B12, and other digested stuffs that were available un-absorbed in the lumen. Ileal and cecocolic ostia generally have a small opening or orifice. A muscular layer circular in shape is the sphincter which is connection of the ileum and the cecum called ileal ostium (ileocecal valve). During dissection of the gastrointestinal tract of donkey, these are the macroscopic structures. In the terminal portion

surface and forming ampulla which is a dilated portion and a sigmoid flexure. The initial curve of the flexure is dorsally convex and the other also called cranial flexure is ventrally convex which provide the site of attachment for body of the pancreas. The first 2 cm of superior part of duodenum, immediately distal to the pylorus has mesentery and is mobile. This free part called the ampulla (duodenal cap). The distal 3 cm of the superior part have no mesentery and are immobile because they are retroperitoneal. The duodenal superior segment ascends from pylorus and is overlapped by the liver. Peritoneum covers its anterior aspects, but it

1.Superior (first) part also called ampulla duodeni

is bare of peritoneum posteriorly, except for the ampulla.

2.Descending (second) part

3.Horizontal (third) part

4.Ascending (fourth) part

**174**

This portion of large intestine has typical similar histological structures to that of cecum including mucosa, submucosa, muscular and serosa. Extensive mucus layer and crypts in the mucosa supports the feces passage. Colon is the lengthiest segment of large intestine and collects nearly entire digested material from the cecum, absorbs the remaining nutrients and water, and permits the drainage of feces to the rectum [7]. The roll of ascending colon is to absorb the remaining water and other key nutrients from the indigestible material, solidifying it to from stool. The waste material (feces) temporarily stored in the descending colon will finally be emptied into the rectum [17]. The rectum is present in pelvic cavity and is dorsal to reproductive tract. It lies between the terminal portion of colon and anus. It is usually found empty except when there is movement of feces with the help of mass movement through large intestine. It may also happen when animal is in the state of hyper aesthesia. Rectum is situated dorsal to genital and urinary tracts. Hence, it is also used for palpation. There is recto-genital pouch at dorsal side of rectum. It is the place where rectum and vagina in female and urethra in male are attached. Meso-rectum is the ligament that is attached to rectum. The rectum has pressure sensitive cells that are activated when it is filled with feces. These special cells are involved in initiation of defecation reflex. This starts the forceful contraction of rectal muscles and internal anal sphincter relaxation. This is the way that feces are passed out. Donkey lacks the ability to control the external anal sphincter. Hence whenever stretch receptors are activated there is a sure or confirmed defecation reflex. In the rectum the columnar epithelium with goblet cells turn to stratified squamous epithelium at recto-anal junction. Circular muscles of tunica muscularis form the internal anal sphincter while that of the other anal sphincter (external) is made up of skeletal muscles that are somewhat of voluntary control. The most terminal portion of the lower GIT is the anal canal which lies between the verge of the anal portion in the perineum bellow and above the rectum (below the level of the pelvic diaphragm) and located in triangular perineum of left and right ischioanal fossa and ultimately it open into the anus. On the basis of the structure, anal canal may be apportioned into two segments (lower and upper) separated by pectinate line or dentate line. Mucosa of the zona columnaris (upper zone) is lined by simple columnar epithelium and the elevation of the mucosa layer produces a valve. It is supplied by superior rectal artery (a branch of the inferior rectal artery). The lower zone is divided into two smaller zones, separated by a line known as Hilton line. The stratified squamous non-keratinized epithelium lining the zona hemorrhagica while the zona cutanea lined stratified squamous keratinized epithelium which blend with the perianal skin. The inferior rectal artery supplies this zone. Anal gland is small gland near the anus in many mammals [27]. Sebaceous gland at the lining of the anal glands secretes some liquid. The medium number of the anal glands in each anus is ranging from (3–10) 85% anal glands were found in the sub mucosa, 7% extended to the internal smooth muscle sphincter and only 2% in the intersphinteric space. Hence these anal glands found in sacs form in the anus and these secret special types of hormones that encourage the other members of that species of opposite sex.

#### **2.13 Microbial digestion of rough and fibrous food in colon of donkey**

Like rumen of the ruminants the microbial digestion mostly accomplished the cecum and colon of the equines. The stomach of ruminants and the large intestine of the donkey are therefore functionally similar. The donkey although is not more efficient in digestive process (grazing) compared to ruminants but has a combination of a large cecum and colon where the process of absorption and fermentation happens. Bacterial counts remain higher in equines where most of the fibrous and

**177**

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*)*

rough food digestion occurs [28]. The higher counts of hemicellulytic and cellulytic bacilli are present in the donkey cecum and in colon the luminal bacterial counts are even more. The intestinal microflora may prevent infection by fighting with pathogens. It is a complex ecosystem containing many bacterial species, protozoa, fungi and yeast. There are five types of microbes present in large intestine includes proteolytic bacteria that cause breakdown of protein, lactic acid bacteria that digest starch, protozoa make volatile fatty acids, cellulytic bacteria and yeast/fungi that digest/break fibers and few vitamin-B producing bacteria. The bacteria that is present in it includes Lactobacillus & Firmicutes in the ileum, Lachnospiraceae, Ruminococcaceae, Bacteroidetes and Spirochetes in the proximal part of large intestine and Prevotellacea in the distal part of large intestine etc. The donkey receives much of its dietary supplement through hydrolysis and by fermentation of

First of all, animal eat food and its whole digestion process is like other animals.

The digestive process like gut motility, absorption, secretion and the blood flow is influenced by the nervous system [30]. Although there is a bit links between the CNC and the digestive system, but the gut is capable of having their own nervous system called as the enteric nervous system (ENS). Like the spinal cord, this system holds numerous neurons. This system alongside with parasympathetic and sympathetic nervous systems establish the autonomic nervous system. The prime constituents of the ENS based on two neurons plexuses (networks) which is implanted along the length of gut wall. The submucosal networks embedded in the submucosa while the myenteric plexus is positioned in muscular externa which regulates motility of the gut. Its key function is in-sensing the intraluminal situation, controlling the mucosal epithelium function and regulating the gut blood flow. In esophagus the submucosal plexus are spars and its function are minimal. Sensory neurons of the mucosa and muscularis receive information from sensory receptors. Almost five diverse mucosal receptors are being known to act to the stimuli

Mastication of food occurs after prehension. Digestion depends on good food grinding by teeth. During mastication saliva is produced and it depends on food which type of food is eaten by donkey. In stomach digestion is minimal and its main function is liquefaction of food then food is drained into small intestine. However, there are many types of enzymes released by stomach. Food particles are broken by gastric acid that produce by stomach. While protein digestion is due to enzyme pepsin. Pancreas release an enzyme called amylase, when food drains into duodenum part of small intestine. This enzyme is less produced in donkeys, so digestion of starch is minimal. The end product of protein is amino acids, done by enzyme released such as pepsin, and it absorb into blood [29]. Volatile fatty acids are produced by process of fermentation and then blood absorbs it. Actually, this volatile fatty act as source of energy. The proteins that remain undigested in large intestine are broken down by enzyme released by microbes. Ammonia is produced by this protein and it is beneficial for growth of beneficial bacteria [20]. Water is absorbed by large intestine, when whole grinded food enters into colon, more reabsorption occurs, and semi-solid feces formed. In colon end step occur as formation of fecal

ball and then move into rectum and then anus [7].

**4. The nervous system of the gastrointestinal tract**

*DOI: http://dx.doi.org/10.5772/intechopen.92722*

these microflora.

**3. Fecal ball formation**

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*) DOI: http://dx.doi.org/10.5772/intechopen.92722*

rough food digestion occurs [28]. The higher counts of hemicellulytic and cellulytic bacilli are present in the donkey cecum and in colon the luminal bacterial counts are even more. The intestinal microflora may prevent infection by fighting with pathogens. It is a complex ecosystem containing many bacterial species, protozoa, fungi and yeast. There are five types of microbes present in large intestine includes proteolytic bacteria that cause breakdown of protein, lactic acid bacteria that digest starch, protozoa make volatile fatty acids, cellulytic bacteria and yeast/fungi that digest/break fibers and few vitamin-B producing bacteria. The bacteria that is present in it includes Lactobacillus & Firmicutes in the ileum, Lachnospiraceae, Ruminococcaceae, Bacteroidetes and Spirochetes in the proximal part of large intestine and Prevotellacea in the distal part of large intestine etc. The donkey receives much of its dietary supplement through hydrolysis and by fermentation of these microflora.

#### **3. Fecal ball formation**

*Equine Science*

This portion of large intestine has typical similar histological structures to that of cecum including mucosa, submucosa, muscular and serosa. Extensive mucus layer and crypts in the mucosa supports the feces passage. Colon is the lengthiest segment of large intestine and collects nearly entire digested material from the cecum, absorbs the remaining nutrients and water, and permits the drainage of feces to the rectum [7]. The roll of ascending colon is to absorb the remaining water and other key nutrients from the indigestible material, solidifying it to from stool. The waste material (feces) temporarily stored in the descending colon will finally be emptied into the rectum [17]. The rectum is present in pelvic cavity and is dorsal to reproductive tract. It lies between the terminal portion of colon and anus. It is usually found empty except when there is movement of feces with the help of mass movement through large intestine. It may also happen when animal is in the state of hyper aesthesia. Rectum is situated dorsal to genital and urinary tracts. Hence, it is also used for palpation. There is recto-genital pouch at dorsal side of rectum. It is the place where rectum and vagina in female and urethra in male are attached. Meso-rectum is the ligament that is attached to rectum. The rectum has pressure sensitive cells that are activated when it is filled with feces. These special cells are involved in initiation of defecation reflex. This starts the forceful contraction of rectal muscles and internal anal sphincter relaxation. This is the way that feces are passed out. Donkey lacks the ability to control the external anal sphincter. Hence whenever stretch receptors are activated there is a sure or confirmed defecation reflex. In the rectum the columnar epithelium with goblet cells turn to stratified squamous epithelium at recto-anal junction. Circular muscles of tunica muscularis form the internal anal sphincter while that of the other anal sphincter (external) is made up of skeletal muscles that are somewhat of voluntary control. The most terminal portion of the lower GIT is the anal canal which lies between the verge of the anal portion in the perineum bellow and above the rectum (below the level of the pelvic diaphragm) and located in triangular perineum of left and right ischioanal fossa and ultimately it open into the anus. On the basis of the structure, anal canal may be apportioned into two segments (lower and upper) separated by pectinate line or dentate line. Mucosa of the zona columnaris (upper zone) is lined by simple columnar epithelium and the elevation of the mucosa layer produces a valve. It is supplied by superior rectal artery (a branch of the inferior rectal artery). The lower zone is divided into two smaller zones, separated by a line known as Hilton line. The stratified squamous non-keratinized epithelium lining the zona hemorrhagica while the zona cutanea lined stratified squamous keratinized epithelium which blend with the perianal skin. The inferior rectal artery supplies this zone. Anal gland is small gland near the anus in many mammals [27]. Sebaceous gland at the lining of the anal glands secretes some liquid. The medium number of the anal glands in each anus is ranging from (3–10) 85% anal glands were found in the sub mucosa, 7% extended to the internal smooth muscle sphincter and only 2% in the intersphinteric space. Hence these anal glands found in sacs form in the anus and these secret special types of hormones that encourage the other members of that species of

**176**

opposite sex.

**2.13 Microbial digestion of rough and fibrous food in colon of donkey**

Like rumen of the ruminants the microbial digestion mostly accomplished the cecum and colon of the equines. The stomach of ruminants and the large intestine of the donkey are therefore functionally similar. The donkey although is not more efficient in digestive process (grazing) compared to ruminants but has a combination of a large cecum and colon where the process of absorption and fermentation happens. Bacterial counts remain higher in equines where most of the fibrous and

First of all, animal eat food and its whole digestion process is like other animals. Mastication of food occurs after prehension. Digestion depends on good food grinding by teeth. During mastication saliva is produced and it depends on food which type of food is eaten by donkey. In stomach digestion is minimal and its main function is liquefaction of food then food is drained into small intestine. However, there are many types of enzymes released by stomach. Food particles are broken by gastric acid that produce by stomach. While protein digestion is due to enzyme pepsin. Pancreas release an enzyme called amylase, when food drains into duodenum part of small intestine. This enzyme is less produced in donkeys, so digestion of starch is minimal. The end product of protein is amino acids, done by enzyme released such as pepsin, and it absorb into blood [29]. Volatile fatty acids are produced by process of fermentation and then blood absorbs it. Actually, this volatile fatty act as source of energy. The proteins that remain undigested in large intestine are broken down by enzyme released by microbes. Ammonia is produced by this protein and it is beneficial for growth of beneficial bacteria [20]. Water is absorbed by large intestine, when whole grinded food enters into colon, more reabsorption occurs, and semi-solid feces formed. In colon end step occur as formation of fecal ball and then move into rectum and then anus [7].

#### **4. The nervous system of the gastrointestinal tract**

The digestive process like gut motility, absorption, secretion and the blood flow is influenced by the nervous system [30]. Although there is a bit links between the CNC and the digestive system, but the gut is capable of having their own nervous system called as the enteric nervous system (ENS). Like the spinal cord, this system holds numerous neurons. This system alongside with parasympathetic and sympathetic nervous systems establish the autonomic nervous system. The prime constituents of the ENS based on two neurons plexuses (networks) which is implanted along the length of gut wall. The submucosal networks embedded in the submucosa while the myenteric plexus is positioned in muscular externa which regulates motility of the gut. Its key function is in-sensing the intraluminal situation, controlling the mucosal epithelium function and regulating the gut blood flow. In esophagus the submucosal plexus are spars and its function are minimal. Sensory neurons of the mucosa and muscularis receive information from sensory receptors. Almost five diverse mucosal receptors are being known to act to the stimuli

including chemical, thermal, mechanical and osmotic origin. The chemoreceptors are sensitive to intraluminal glucose, acid, and amino acids. The muscular sensory receptors are reacting to all kinds of tension and stretch. The ENS are collectively gathering the evidence on condition of the gut wall and its luminal contents and motor neurons controlling the intraluminal absorption and secretion along with gut motility. Motor neurons act directly on many effector cells, including secretory cells viz. parietal, chief, enterocytes, mucous, gut endocrine, pancreatic exocrine cells and the smooth muscle cells [31]. The interneurons of the intestine are liable for assimilating information from sensory neurons and delivering it to motor neurons. In autonomic nervous system the T5, T6, T7, T8 make greater splanchnic nerve of which splanchnic ganglion and celiac ganglion are formed that further form celiac plexus (that supplies the stomach). The T11, T12 make least splanchnic nerve of which superior enteric plexus and inferior enteric plexus are formed that further innervates intestines. The L1, L2, L3 also innervates intestines. Sympathetic nervous system includes S2, S3, S4 forms pelvic nerve that supplies intestines and C10 innervates both stomach and the intestines. Ganglions including celiacomesenteric ganglion and caudal mesenteric ganglion and the lumbosacral plexus (hypogastric nerve) also innervates stomach.

#### **5. Accessary glandular structures**

All three major salivary glands are composed of either serous acini, mucous acini, or a combination of both. While parotid gland is largest of the three. All glands function is to produce saliva to moisturize the mouth and assist in the breakdown of carbohydrates in the mouth. The submandibular gland is the primary source of basal saliva secretion [32], while the parotid gland is the main source of stimulated saliva secretion. Salivary glands also play a crucial immunologic role as their secretions contain many immunoglobins, namely IgA, that help fight bacteria and other foreign antigens in the oropharyngeal environment. The sublingual glands lie inferolateral to the tongue, below the floor of the mouth and above the mylohyoid muscle [18]. Sublingual tissue is also palpable and is an oval shaped when sectioned transversely, however, its shape is longitudinal and lentiform when sectioned parallel to the body of the mandible. The sublingual gland differs from the other major salivary glands, because it lacks intercalated or striated ducts, so the saliva secretes directly through the ducts of Rivinus. These ducts empty along an elevated ridge called the plica fimbriata formed by the sublingual folds, which are oblique to the frenulum linguae bilaterally. The sublingual duct of Bartholin joins Wharton's duct to form the draining orifice on each side of the lingual frenulum. The sublingual tissue is predominantly a mucous gland, however, is considered a mixed serous and mucous gland. It is made up of mainly mucous acini with serous demilunes at periphery. It is the only unencapsulated major salivary gland. Sublingual tissue primarily produces a thick mucinous fluid and lubricates the oral cavity which allows for swallowing, initiating digestion, buffering pH, and dental hygiene. It retains both serous and mucous acinar cells while parotid salivary glands possess predominantly serous acini and produces watery fluid [17]. Myoepithelial cells are present around the acinar cells. The mandibular is tubule-acinar seromucous gland. The myoepithelial cells are present around the secretory units. Cells of the mucous acini have a pale-staining foamy cytoplasm which pushed the nuclei toward the basal lamina. While, the serous cells cytoplasm has zymogen granules (markedly eosinophilic) and their nuclei having rounded shape. The secretory acini which is made up of collection of secretory cells are categorized into serous and mucous category. The serous acini have just spherical shaped serous cells and

**179**

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*)*

the mucous acini have only tubular shaped mucous cells. The sero-mucous (mixed) acini hold a combination of mucous and serous cells [6]. In histological set sections of the tissue, the swell mucous cells push the serous cells into a marginal area forming cap like structure recognized as serous demilune (demilune = "half-moon"). The submandibular gland obtains the supply of blood from lingual and facial arteries and emptied by shared lingual and facial veins. The parotid is supplied through the carotid artery (external) and its terminal branches including the superficial temporal and the maxillary artery and emptied by the retromandibular veins. The sublingual glands receive its blood supply from the submental and sublingual

Liver is the principal gland having no gall bladder. Its left side lobe is divided further. It is found underneath the diaphragm and protected by the ribs. It is covered by a fibrous connective tissue capsule, known as Glisson's capsule, which penetrates deep into the organ parenchyma to form septa that divide the main organ into lobes. The liver is formed from an invagination of the digestive tube during the embryonic development; therefore, it is an epithelial derivative [6]. The cellular organization of the liver is relatively simple based on the repetition of a basic structure called hepatic lobule. Lobules are separated from each other by connective tissue. The morphology of lobules is like polygonal prisms, of about 1–2 mm in diameter, and, in cross-sections, the lobules are similar to a hexagon containing a central vein of large diameter [33]. Hepatocytes represent more than 75% of the liver and are organized in anastomosed layers, or trabeculae. These layers of hepatocytes are usually one-cell thick and fused together to form a complex structure similar to a sponge. Small diameter sinusoids run between the layers of hepatocytes [34]. Between the endothelium of sinusoids and hepatocytes there are free-cellular spaces known as perisinusoidal spaces or spaces of Disse. Hepatocytes release two types of substances: endocrine toward sinusoids and exocrine toward the bile canaliculi. Hepatocytes are relatively large (around 20–30 μm) with a rounded nucleus, some are binucleated, and most of them are tetraploid. Hepatocytes are epithelial cells polygonal in shape having rich eosinophilic granular cytoplasm and centrally placed large spherical nuclei with conspicuous nucleolus. Hepatocytes having two nuclei are also common. Cells having numerous SER and RER, several mitochondria and Golgi apparatus. Hepatocytes are arranged in form of cords and the cells are separated by sinusoidal spaces called sinusoids. These are capillaries and are lined by flattened nucleated endothelial cells. The portal tirades constituted hepatic artery, portal vein and bile duct within the connective tissue are located at the portal areas between nearby lobules [35]. Portal triads are constituted by a branch of the portal vein (venule), a branch of the hepatic artery (arteriole) and a bile duct. In addition, lymphatic vessels and nerve fibers are found in the portal areas. The bile ducts of the portal triad collect the exocrine content, or bile, produced by the hepatocytes. Bile flows in the opposite direction to the blood that runs through the sinusoidal capillaries, in other words, it is directed from the hepatocytes to the bile ducts of the periphery of the hepatic lobule (the portal areas). This is possible because the plasma membranes of adjoining hepatocytes form interconnected spaces, the bile canaliculi, which are organized in an anastomosed network that finally fuses with the bile ducts. Ito cells (stellate cells/lipocytes) exist in space of Disse (between hepatocytes and endothelial cells). Kupffer cells are round in shape positioned in the sinusoids at vascular space within sinusoids [36]. Oval cells (pluripotent stem cells) are also present in the liver. Short lived lymphocytes (pit

*DOI: http://dx.doi.org/10.5772/intechopen.92722*

arteries.

**6. Liver**

#### *Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*) DOI: http://dx.doi.org/10.5772/intechopen.92722*

the mucous acini have only tubular shaped mucous cells. The sero-mucous (mixed) acini hold a combination of mucous and serous cells [6]. In histological set sections of the tissue, the swell mucous cells push the serous cells into a marginal area forming cap like structure recognized as serous demilune (demilune = "half-moon"). The submandibular gland obtains the supply of blood from lingual and facial arteries and emptied by shared lingual and facial veins. The parotid is supplied through the carotid artery (external) and its terminal branches including the superficial temporal and the maxillary artery and emptied by the retromandibular veins. The sublingual glands receive its blood supply from the submental and sublingual arteries.

#### **6. Liver**

*Equine Science*

nerve) also innervates stomach.

**5. Accessary glandular structures**

including chemical, thermal, mechanical and osmotic origin. The chemoreceptors are sensitive to intraluminal glucose, acid, and amino acids. The muscular sensory receptors are reacting to all kinds of tension and stretch. The ENS are collectively gathering the evidence on condition of the gut wall and its luminal contents and motor neurons controlling the intraluminal absorption and secretion along with gut motility. Motor neurons act directly on many effector cells, including secretory cells viz. parietal, chief, enterocytes, mucous, gut endocrine, pancreatic exocrine cells and the smooth muscle cells [31]. The interneurons of the intestine are liable for assimilating information from sensory neurons and delivering it to motor neurons. In autonomic nervous system the T5, T6, T7, T8 make greater splanchnic nerve of which splanchnic ganglion and celiac ganglion are formed that further form celiac plexus (that supplies the stomach). The T11, T12 make least splanchnic nerve of which superior enteric plexus and inferior enteric plexus are formed that further innervates intestines. The L1, L2, L3 also innervates intestines. Sympathetic nervous system includes S2, S3, S4 forms pelvic nerve that supplies intestines and C10 innervates both stomach and the intestines. Ganglions including celiacomesenteric ganglion and caudal mesenteric ganglion and the lumbosacral plexus (hypogastric

All three major salivary glands are composed of either serous acini, mucous acini, or a combination of both. While parotid gland is largest of the three. All glands function is to produce saliva to moisturize the mouth and assist in the breakdown of carbohydrates in the mouth. The submandibular gland is the primary source of basal saliva secretion [32], while the parotid gland is the main source of stimulated saliva secretion. Salivary glands also play a crucial immunologic role as their secretions contain many immunoglobins, namely IgA, that help fight bacteria and other foreign antigens in the oropharyngeal environment. The sublingual glands lie inferolateral to the tongue, below the floor of the mouth and above the mylohyoid muscle [18]. Sublingual tissue is also palpable and is an oval shaped when sectioned transversely, however, its shape is longitudinal and lentiform when sectioned parallel to the body of the mandible. The sublingual gland differs from the other major salivary glands, because it lacks intercalated or striated ducts, so the saliva secretes directly through the ducts of Rivinus. These ducts empty along an elevated ridge called the plica fimbriata formed by the sublingual folds, which are oblique to the frenulum linguae bilaterally. The sublingual duct of Bartholin joins Wharton's duct to form the draining orifice on each side of the lingual frenulum. The sublingual tissue is predominantly a mucous gland, however, is considered a mixed serous and mucous gland. It is made up of mainly mucous acini with serous demilunes at periphery. It is the only unencapsulated major salivary gland. Sublingual tissue primarily produces a thick mucinous fluid and lubricates the oral cavity which allows for swallowing, initiating digestion, buffering pH, and dental hygiene. It retains both serous and mucous acinar cells while parotid salivary glands possess predominantly serous acini and produces watery fluid [17]. Myoepithelial cells are present around the acinar cells. The mandibular is tubule-acinar seromucous gland. The myoepithelial cells are present around the secretory units. Cells of the mucous acini have a pale-staining foamy cytoplasm which pushed the nuclei toward the basal lamina. While, the serous cells cytoplasm has zymogen granules (markedly eosinophilic) and their nuclei having rounded shape. The secretory acini which is made up of collection of secretory cells are categorized into serous and mucous category. The serous acini have just spherical shaped serous cells and

**178**

Liver is the principal gland having no gall bladder. Its left side lobe is divided further. It is found underneath the diaphragm and protected by the ribs. It is covered by a fibrous connective tissue capsule, known as Glisson's capsule, which penetrates deep into the organ parenchyma to form septa that divide the main organ into lobes. The liver is formed from an invagination of the digestive tube during the embryonic development; therefore, it is an epithelial derivative [6]. The cellular organization of the liver is relatively simple based on the repetition of a basic structure called hepatic lobule. Lobules are separated from each other by connective tissue. The morphology of lobules is like polygonal prisms, of about 1–2 mm in diameter, and, in cross-sections, the lobules are similar to a hexagon containing a central vein of large diameter [33]. Hepatocytes represent more than 75% of the liver and are organized in anastomosed layers, or trabeculae. These layers of hepatocytes are usually one-cell thick and fused together to form a complex structure similar to a sponge. Small diameter sinusoids run between the layers of hepatocytes [34]. Between the endothelium of sinusoids and hepatocytes there are free-cellular spaces known as perisinusoidal spaces or spaces of Disse. Hepatocytes release two types of substances: endocrine toward sinusoids and exocrine toward the bile canaliculi. Hepatocytes are relatively large (around 20–30 μm) with a rounded nucleus, some are binucleated, and most of them are tetraploid. Hepatocytes are epithelial cells polygonal in shape having rich eosinophilic granular cytoplasm and centrally placed large spherical nuclei with conspicuous nucleolus. Hepatocytes having two nuclei are also common. Cells having numerous SER and RER, several mitochondria and Golgi apparatus. Hepatocytes are arranged in form of cords and the cells are separated by sinusoidal spaces called sinusoids. These are capillaries and are lined by flattened nucleated endothelial cells. The portal tirades constituted hepatic artery, portal vein and bile duct within the connective tissue are located at the portal areas between nearby lobules [35]. Portal triads are constituted by a branch of the portal vein (venule), a branch of the hepatic artery (arteriole) and a bile duct. In addition, lymphatic vessels and nerve fibers are found in the portal areas. The bile ducts of the portal triad collect the exocrine content, or bile, produced by the hepatocytes. Bile flows in the opposite direction to the blood that runs through the sinusoidal capillaries, in other words, it is directed from the hepatocytes to the bile ducts of the periphery of the hepatic lobule (the portal areas). This is possible because the plasma membranes of adjoining hepatocytes form interconnected spaces, the bile canaliculi, which are organized in an anastomosed network that finally fuses with the bile ducts. Ito cells (stellate cells/lipocytes) exist in space of Disse (between hepatocytes and endothelial cells). Kupffer cells are round in shape positioned in the sinusoids at vascular space within sinusoids [36]. Oval cells (pluripotent stem cells) are also present in the liver. Short lived lymphocytes (pit

cells) are situated in the sinusoids. The coeliac artery branched in hepatic artery and portal vein is fashioned by tributaries draining the pancreas, digestive tract and spleen [37]. Blood flows from the portal areas into the central vein lined by simple squamous epithelium. The blood vessels, nerves and bile duct leave and enter the liver at the hepatic porta.

#### **7. Pancreas**

The pancreas is encapsulated and lobulated organs having both the endocrine and exocrine portions. The color of the pancreas of the donkey is reddish cream. The connective tissue stroma divides the parenchyma into various lobules having secretory units and the intralobular duct. The pancreas is triangular, tubuloacinar gland and is present aside from the duodenum [35]. It consists of a body, right lobe, and left lobe. The pancreas has pyramidal acinar cells. Apical portions of these cells have secretory granules (zymogen granules). Exocrine portion produces several enzymes while the Islets of Langerhans are the endocrine portion of this gland. Alfa, beta and delta cells of the islets produces glucagon, insulin and somatostatin respectively [36]. Glandular tissue from the caudal end of the right lobe extended over the portal vein to the left lobe thus forming a ring. The pancreas secretes digestive enzymes into duodenum such as amylase, lipase and trypsin through pancreatic duct. These enzymes digest the carbohydrates, lipids and protein part of feed. The main pancreatic ducts which empties into the duodenum is the extension of interlobular duct, intralobular duct, and intercalated duct. The body of the pancreas received its blood supply from pancreatic branches of the gastroduodenal artery, the first branch was the larger one and originated from the gastroduodenal artery just after its origin from the hepatic artery, the second smaller branch has originated just before the gastroduodenal artery distributed into cranial pancreaticoduodenal and right gastroepiploic arteries. The left lobe received its blood supply from hepatic and splenic artery. The right lobe established its supply of blood from the cranial mesenteric artery.

#### **8. Mucosa associated lymphatic tissues**

Mucosa-associated lymphoid tissue (MALT) defends the body from gut invasion of pathogens. The mucosae of the respiratory, urinary and digestive tracts often have few aggregated lymphocytes called MALT or lymphoid follicles [38]. It is situated in different portions of the body viz. nasopharynx, lungs, breast, thyroid, eye, salivary glands, skin and GI tract. MALT is made-up of B and T lymphocytes, macrophages and plasma cells. In the case of intestinal MALT, there are also M cells that take antigen from the lumen and deliver it to the lymphoid tissue. MALT constitutes about 50% of the lymphoid tissue in animal body and its components are sometimes divided into the following areas/types: GALT (lymphoid tissue associated with the intestine. Peyer patches are a component of GALT, which is found in the lining of the small intestine), BALT (lymphoid tissue associated with bronchi), NALT (nasal associated lymphoid tissue), CALT (conjunctiva-associated lymphoid tissue), LALT (lymphoid tissue associated with the larynx), SALT (skin-associated lymphatic tissue), VALT (lymphoid tissue associated with vulvovaginal) and TALT (lymphoid tissue associated with testicular). It can also be distinguished by the degree of tissue organization: O-MALT (lymphoid tissue associated with the organized mucosa), D-MALT (diffuse lymphoid tissue of the mucosa). The MALT that is not organized as a mass, tissue or organ anatomically identifiable separately macroscopically (like

**181**

**Author details**

**9. Conclusion**

**Acknowledgements**

Attendant, Histology section, CVAS, Jhang.

Arbab Sikandar

Lahore, Pakistan

drarbab786@gmail.com

provided the original work is properly cited.

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*)*

the O-MALT mentioned above) is diffuse MALT. Due to its function during food intake, the mucous membrane is superficially slim and performed as permeable barrier in the body. Likewise, its permeability and delicateness make it susceptible to infection, and in fact most infectious agents that enter the body practice this way. GALT as protection mostly depends on plasma cells that produce antibodies. The lymphatic tissue associated with the intestine is found throughout the intestine and histopathology is the better option to study those [39]. Like thymocytes, GALT containing intestinal Peyer patches (lymphoid follicles made up of lymphocytes) are responsible to safeguard the animal health from the gut luminal side [40, 41].

The morphophysiological study both (gross and microscopic) of the gastrointestinal tract and associated structures of domestic donkeys are very important to document. The microstructure of internal luminal layer of the gut, luminal ecosys-

The author would like to acknowledge the typing efforts of Mr. Saqib Ali, Jr. Lab.

tem, immunity and function of the gut is highlighted in this chapter.

Department of Basic Sciences, University of Veterinary and Animal Sciences,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to: arbab.sikandar@uvas.edu.pk;

*DOI: http://dx.doi.org/10.5772/intechopen.92722*

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*) DOI: http://dx.doi.org/10.5772/intechopen.92722*

the O-MALT mentioned above) is diffuse MALT. Due to its function during food intake, the mucous membrane is superficially slim and performed as permeable barrier in the body. Likewise, its permeability and delicateness make it susceptible to infection, and in fact most infectious agents that enter the body practice this way. GALT as protection mostly depends on plasma cells that produce antibodies. The lymphatic tissue associated with the intestine is found throughout the intestine and histopathology is the better option to study those [39]. Like thymocytes, GALT containing intestinal Peyer patches (lymphoid follicles made up of lymphocytes) are responsible to safeguard the animal health from the gut luminal side [40, 41].

#### **9. Conclusion**

*Equine Science*

**7. Pancreas**

liver at the hepatic porta.

the cranial mesenteric artery.

**8. Mucosa associated lymphatic tissues**

cells) are situated in the sinusoids. The coeliac artery branched in hepatic artery and portal vein is fashioned by tributaries draining the pancreas, digestive tract and spleen [37]. Blood flows from the portal areas into the central vein lined by simple squamous epithelium. The blood vessels, nerves and bile duct leave and enter the

The pancreas is encapsulated and lobulated organs having both the endocrine and exocrine portions. The color of the pancreas of the donkey is reddish cream. The connective tissue stroma divides the parenchyma into various lobules having secretory units and the intralobular duct. The pancreas is triangular, tubuloacinar gland and is present aside from the duodenum [35]. It consists of a body, right lobe, and left lobe. The pancreas has pyramidal acinar cells. Apical portions of these cells have secretory granules (zymogen granules). Exocrine portion produces several enzymes while the Islets of Langerhans are the endocrine portion of this gland. Alfa, beta and delta cells of the islets produces glucagon, insulin and somatostatin respectively [36]. Glandular tissue from the caudal end of the right lobe extended over the portal vein to the left lobe thus forming a ring. The pancreas secretes digestive enzymes into duodenum such as amylase, lipase and trypsin through pancreatic duct. These enzymes digest the carbohydrates, lipids and protein part of feed. The main pancreatic ducts which empties into the duodenum is the extension of interlobular duct, intralobular duct, and intercalated duct. The body of the pancreas received its blood supply from pancreatic branches of the gastroduodenal artery, the first branch was the larger one and originated from the gastroduodenal artery just after its origin from the hepatic artery, the second smaller branch has originated just before the gastroduodenal artery distributed into cranial pancreaticoduodenal and right gastroepiploic arteries. The left lobe received its blood supply from hepatic and splenic artery. The right lobe established its supply of blood from

Mucosa-associated lymphoid tissue (MALT) defends the body from gut invasion

of pathogens. The mucosae of the respiratory, urinary and digestive tracts often have few aggregated lymphocytes called MALT or lymphoid follicles [38]. It is situated in different portions of the body viz. nasopharynx, lungs, breast, thyroid, eye, salivary glands, skin and GI tract. MALT is made-up of B and T lymphocytes, macrophages and plasma cells. In the case of intestinal MALT, there are also M cells that take antigen from the lumen and deliver it to the lymphoid tissue. MALT constitutes about 50% of the lymphoid tissue in animal body and its components are sometimes divided into the following areas/types: GALT (lymphoid tissue associated with the intestine. Peyer patches are a component of GALT, which is found in the lining of the small intestine), BALT (lymphoid tissue associated with bronchi), NALT (nasal associated lymphoid tissue), CALT (conjunctiva-associated lymphoid tissue), LALT (lymphoid tissue associated with the larynx), SALT (skin-associated lymphatic tissue), VALT (lymphoid tissue associated with vulvovaginal) and TALT (lymphoid tissue associated with testicular). It can also be distinguished by the degree of tissue organization: O-MALT (lymphoid tissue associated with the organized mucosa), D-MALT (diffuse lymphoid tissue of the mucosa). The MALT that is not organized as a mass, tissue or organ anatomically identifiable separately macroscopically (like

**180**

The morphophysiological study both (gross and microscopic) of the gastrointestinal tract and associated structures of domestic donkeys are very important to document. The microstructure of internal luminal layer of the gut, luminal ecosystem, immunity and function of the gut is highlighted in this chapter.

#### **Acknowledgements**

The author would like to acknowledge the typing efforts of Mr. Saqib Ali, Jr. Lab. Attendant, Histology section, CVAS, Jhang.

#### **Author details**

Arbab Sikandar Department of Basic Sciences, University of Veterinary and Animal Sciences, Lahore, Pakistan

\*Address all correspondence to: arbab.sikandar@uvas.edu.pk; drarbab786@gmail.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[11] Abd-Elnaeim MM, Zayed AE, Leiser R. Morphological characteristics of the tongue and its papillae in the donkey (*Equus asinus*): A light and scanning electron microscopical study. Annals of Anatomy-Anatomischer Anzeiger. 2002;**184**(5):473-480

[12] Du Toit N, Kempson SA, Dixon PM. Donkey dental anatomy. Part 1: Gross and computed axial tomography examinations. The Veterinary Journal. 2008;**176**(3):338-344

[13] Mohamed RA, Zaki MF. Applied anatomy of the head region of donkey (*Equus asinus*) in Egypt and its clinical value during regional anesthesia. International Journal of Current Research and Academic Review. 2015;**3**:45-58

[14] El-Gendy SAA, Alsafy MAM, El Sharaby AA. Computed tomography and sectional anatomy of the head cavities in donkey (*Equus asinus*). Anatomical Science International. 2014;**89**(3):140-150

[15] Lindsay FE, Clayton HM. An anatomical and endoscopic study of the nasopharynx and larynx of the donkey

**183**

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*)*

Rehman T. Histopathological and serological studies on paratuberculosis in cattle and buffaloes. Pakistan Veterinary Journal. 2012;**4**:547-551

[24] Sikandar A, Adil M, Ansari AR, Nasir A, Rehman TU, Raza hameed M, et al. Histological evaluation of the gut of Nili-Ravi buffaloes for diagnosing paratuberculosis. Buffalo Bulletin.

[25] Sikandar A, Zaneb H, Younus M, Masood S, Aslam A, Shah M, et al. Growth performance, immune status and organ morphometry in broilers fed *Bacillus subtilis*supplemented diet. South African Journal of Animal Science.

[26] Arbab S, Cheema AH, Adil M, Younus M, Zaneb H, Zaman A, et al. Ovine paratuberculosis—A histopathological study from Pakistan. The Journal of Animal and Plant Sciences.

2014;**33**(4):370-375

2017;**47**(3):378-388

2013;**23**(3):749-753

2019;**14**:1-14

2004;**88**(1-2):7-19

2020;**88**:102943

[27] Seow-Choen F, Ho JM.

of the Colon & Rectum. 1994;**37**(12):1215-1218

Histoanatomy of anal glands. Diseases

[28] Liu G, Bou G, Shaofeng S, Xing J, Honglei Q, Zhang X, et al. Microbial diversity within the digestive tract contents of Dezhou donkeys. PLoS One.

[29] Zeyner A, Geißler C, Dittrich A. Effects of hay intake and feeding sequence on variables in faeces and faecal water (dry matter, pH value, organic acids, ammonia, buffering capacity) of horses. Journal of Animal Physiology and Animal Nutrition.

[30] Garber A, Hastie P, Murray JA. Factors influencing equine gut microbiota: Current knowledge. Journal of Equine Veterinary Science.

*DOI: http://dx.doi.org/10.5772/intechopen.92722*

(*Equus asinus*). Journal of Anatomy.

[16] Fores P, Lopez J, Rodriguez A, Harran R. Endoscopy of the upper airways and the proximal digestive tract in the donkey (*Equus asinus*). Journal of Equine Veterinary Science.

[17] Jerbi H, Rejeb A, Erdoğan S,

study of gastrointestinal tract of donkey (*Equus africanus asinus*). Journal of Morphological Sciences.

[18] Herman CL. The anatomical differences between the donkey and the horse. In: Veterinary Care of Donkeys. Ithaca NY: International Veterinary

[19] Aganga AA, Letso M, Aganga AO. Feeding donkeys. Livestock Research for Rural Development. 2000;**12**(2):2000

[20] Pearson RA. Nutrition and feeding of donkeys. In: Mathews NS, Taylor TS, editors. Veterinary Care of Donkeys. Ithaca NY: International Veterinary

[21] Sikandar A, Zaneb H, Younus M, Masood S, Aslam A, Khattak F, et al. Effect of sodium butyrate on performance, immune status, microarchitecture of small intestinal mucosa and lymphoid organs in broiler chickens. Asian-Australasian Journal of Animal Sciences. 2017a;**30**(5):690

[22] Sikandar A, Zaneb H, Younus M, Masood S, Aslam A, Ashraf S, et al. Protective effect of sodium butyrate on growth performance, immune responses and gut mucosal morphometry in *Salmonella*-challenged broiler chickens. International Journal of Agriculture and

Biology. 2017b;**19**(6):1387-1393

[23] Sikandar A, Cheema AH, Younus M, Aslam A, Zaman MA,

Information Service; 2009

Information Service; 2005

Pérez W. Anatomical and morphometric

1986;**144**:123

2001;**21**(1):17-20

2014;**31**(01):018-022

*Morphophysiological Study of Gastrointestinal Tract of the Donkey (*Equus asinus*) DOI: http://dx.doi.org/10.5772/intechopen.92722*

(*Equus asinus*). Journal of Anatomy. 1986;**144**:123

[16] Fores P, Lopez J, Rodriguez A, Harran R. Endoscopy of the upper airways and the proximal digestive tract in the donkey (*Equus asinus*). Journal of Equine Veterinary Science. 2001;**21**(1):17-20

[17] Jerbi H, Rejeb A, Erdoğan S, Pérez W. Anatomical and morphometric study of gastrointestinal tract of donkey (*Equus africanus asinus*). Journal of Morphological Sciences. 2014;**31**(01):018-022

[18] Herman CL. The anatomical differences between the donkey and the horse. In: Veterinary Care of Donkeys. Ithaca NY: International Veterinary Information Service; 2009

[19] Aganga AA, Letso M, Aganga AO. Feeding donkeys. Livestock Research for Rural Development. 2000;**12**(2):2000

[20] Pearson RA. Nutrition and feeding of donkeys. In: Mathews NS, Taylor TS, editors. Veterinary Care of Donkeys. Ithaca NY: International Veterinary Information Service; 2005

[21] Sikandar A, Zaneb H, Younus M, Masood S, Aslam A, Khattak F, et al. Effect of sodium butyrate on performance, immune status, microarchitecture of small intestinal mucosa and lymphoid organs in broiler chickens. Asian-Australasian Journal of Animal Sciences. 2017a;**30**(5):690

[22] Sikandar A, Zaneb H, Younus M, Masood S, Aslam A, Ashraf S, et al. Protective effect of sodium butyrate on growth performance, immune responses and gut mucosal morphometry in *Salmonella*-challenged broiler chickens. International Journal of Agriculture and Biology. 2017b;**19**(6):1387-1393

[23] Sikandar A, Cheema AH, Younus M, Aslam A, Zaman MA, Rehman T. Histopathological and serological studies on paratuberculosis in cattle and buffaloes. Pakistan Veterinary Journal. 2012;**4**:547-551

[24] Sikandar A, Adil M, Ansari AR, Nasir A, Rehman TU, Raza hameed M, et al. Histological evaluation of the gut of Nili-Ravi buffaloes for diagnosing paratuberculosis. Buffalo Bulletin. 2014;**33**(4):370-375

[25] Sikandar A, Zaneb H, Younus M, Masood S, Aslam A, Shah M, et al. Growth performance, immune status and organ morphometry in broilers fed *Bacillus subtilis*supplemented diet. South African Journal of Animal Science. 2017;**47**(3):378-388

[26] Arbab S, Cheema AH, Adil M, Younus M, Zaneb H, Zaman A, et al. Ovine paratuberculosis—A histopathological study from Pakistan. The Journal of Animal and Plant Sciences. 2013;**23**(3):749-753

[27] Seow-Choen F, Ho JM. Histoanatomy of anal glands. Diseases of the Colon & Rectum. 1994;**37**(12):1215-1218

[28] Liu G, Bou G, Shaofeng S, Xing J, Honglei Q, Zhang X, et al. Microbial diversity within the digestive tract contents of Dezhou donkeys. PLoS One. 2019;**14**:1-14

[29] Zeyner A, Geißler C, Dittrich A. Effects of hay intake and feeding sequence on variables in faeces and faecal water (dry matter, pH value, organic acids, ammonia, buffering capacity) of horses. Journal of Animal Physiology and Animal Nutrition. 2004;**88**(1-2):7-19

[30] Garber A, Hastie P, Murray JA. Factors influencing equine gut microbiota: Current knowledge. Journal of Equine Veterinary Science. 2020;**88**:102943

**182**

*Equine Science*

**References**

2013;**1**:304-316

pp. 295-317

[1] Smith DG, Burden FA. Practical donkey and mule nutrition. Equine Applied and Clinical Nutrition.

behavior. The Veterinary Clinics of North America. Equine Practice.

Dixon PM. Donkey dental anatomy. Part 2: Histological and scanning electron microscopic examinations. The Veterinary Journal. 2008;**176**(3):345-353

Kempson SA, Dixon PM. Pathological investigation of caries and occlusal pulpar exposure in donkey cheek teeth using computerised axial tomography with histological and ultrastructural examinations. The Veterinary Journal.

[11] Abd-Elnaeim MM, Zayed AE, Leiser R. Morphological characteristics of the tongue and its papillae in the donkey (*Equus asinus*): A light and scanning electron microscopical study. Annals of Anatomy-Anatomischer Anzeiger. 2002;**184**(5):473-480

[12] Du Toit N, Kempson SA, Dixon PM. Donkey dental anatomy. Part 1: Gross and computed axial tomography examinations. The Veterinary Journal.

[13] Mohamed RA, Zaki MF. Applied anatomy of the head region of donkey (*Equus asinus*) in Egypt and its clinical value during regional anesthesia. International Journal of Current Research and Academic Review.

[14] El-Gendy SAA, Alsafy MAM, El Sharaby AA. Computed tomography and sectional anatomy of the head cavities in donkey (*Equus asinus*). Anatomical Science International.

[15] Lindsay FE, Clayton HM. An anatomical and endoscopic study of the nasopharynx and larynx of the donkey

2019;**35**(3):575-588

[9] Du Toit N, Kempson SA,

[10] Du Toit N, Burden FA,

2008;**178**(3):387-395

2008;**176**(3):338-344

2015;**3**:45-58

2014;**89**(3):140-150

[2] Clarence-Smith WG. Mules in the Indian Ocean world: Breeding and trade in the long nineteenth century, 1780s to 1918. In: Early Global Interconnectivity across the Indian Ocean World. Vol. 2. Cham: Palgrave Macmillan; 2019.

[3] Macdonald J. Supplying the British Army in the Second World War. Great Britain: Pen and Sword Military; 2020

[5] Li X, Amadou I, Zhou GY, Qian LY, Zhang JL, Wang DL, et al. Flavor components comparison between the neck meat of donkey, swine, bovine and sheep. Food Science of Animal

[6] Tisserand JL, Faurie F, Toure M. Comparative study of donkey and pony digestive physiology. In: Donkeys, Mules & Horses in Tropical Agricultural Development: Proc of a Colloquium Organ by the Edinburgh School of Agric & the Cent for Trop Vet Med of the Univ of Edinburgh; 3-6 September 1990; Edinburgh, Scotland. Edinburgh: Centre for Tropical Veterinary Medicine; 1991

[7] Van Weyenberg S, Sales J, Janssens GPJ. Passage rate of digesta through the equine gastrointestinal tract: A review. Livestock Science.

[8] McLean AK, González FJN, Canisso IF. Donkey and mule

2006;**99**(1):3-12

Resources. 2020;**40**:1-25

[4] Li M, Kang S, Zheng Y, Shao J, Zhao H, An Y, et al. Comparative metabolomics analysis of donkey colostrum and mature milk using ultra-high-performance liquid tandem chromatography quadrupole time-offlight mass spectrometry. Journal of Dairy Science. 2020;**103**(1):992-1001

[31] Spencer NJ, Hu H. Enteric nervous system: Sensory transduction, neural circuits and gastrointestinal motility. Nature Reviews Gastroenterology & Hepatology. 2020;**17**:338-351

[32] Barka T. Biologically active polypeptides in submandibular glands. The Journal of Histochemistry and Cytochemistry. 1980;**28**(8):836-859

[33] Zhang W, Mei N, Qian L, Xie X, Fan Y, Zhao H, et al. Comparison of nutrients between donkey liver and pig liver, chicken liver and goose liver. Journal of Food Safety and Quality. 2018;**9**(16):4435-4439

[34] Sikandar A, Cheema AH, Younus M, Zaneb H. *Mycobacterium avium* subspecies paratuberculosis multibacillary infection (Johne's disease) in at teddy goat. Pakistan Veterinary Journal. 2012;**33**(2):260-262

[35] König HE, Liebich HG, editors. Veterinary Anatomy of Domestic Mammals: Textbook and Colour Atlas. New York: Schattauer Verlag; 2013

[36] Eurell JN, Frappier BL. Textbook of Veterinary Histology. 6th ed. USA: Blackwell Publishing; 2006

[37] Karakurum E, Dursun N. Arterial vascularisation of liver and spleen in donkey (*Equus asinus* L.). Sağlık Bilimleri Veteriner Dergisi, Fırat Üniversitesi. 2014;**28**(2):73-76

[38] Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th ed. USA: Blackwell Publishing; 2009

[39] Sikandar A. Histopathology: An old yet important technique in modern science. In: Histopathology—An Update. IntechOpen; 2018

[40] Sikandar A, Ullah N. Microarchitecture of the thymus gland; its age and disease-associated

morphological alterations, and possible means to prolong its physiological activity. In: Thymus. London, UK: IntechOpen Ltd; 2020

[41] Spahn TW, Kucharzik T. Modulating the intestinal immune system: The role of lymphotoxin and GALT organs. Gut. 2004;**53**(3):456-465

**185**

**Chapter 10**

Programme

*Stéphanie Cassigneul*

**Abstract**

faecal egg count

**1. Introduction**

Promoting Grass in Horse Diets

and Implementing Sustainable

Deworming: 'Équipâture'

*Pauline Doligez, Marie Delerue, Agnès Orsoni,* 

*Guillaume Mathieu, Jean Baptiste Quillet and* 

*Bathilde Diligeon, Céline Saillet, Hervé Feugère,* 

The Équipâture programme examined the grazing regimes and parasite statuses of horses on 12 study farms. Its research yielded useful results. Rotational grazing of mares, foals, and school riding horses allowed animals to meet their nutritional needs without any supplements (50 ares/LU in the spring; 80 ares/LU in the summer). During the winter, haylage met the high demands of mares and foals. Late-cut hay could not, and there was a risk of P, Cu, and Zn deficiencies when horses were given a 100% hay diet. A sustainable approach to deworming was implemented on the farms. Based on faecal analysis, animals were assigned a parasite excretion status. As a result of this categorisation, only half of the animals were dewormed. This method helped limit deworming costs and the development of parasite resistance to dewormers.

**Keywords:** horse grazing, stocking rate, hay, haylage grass analysis, deworming,

Grass, although being the most adapted food and considered as the least costly for herbivores, is nevertheless not always duly promoted in equine diets. The lack of data on equine pasture management and systematic deworming practices are recorded as factors hampering the efficient and sustainable management of grazing horses [1]. Systematic and frequent deworming of horses encourages the development of parasite resistance to dewormers. Three active dewormer families against cyathostomins, the most prevalent parasite in adult horses, are currently available on the market in France. Among the said three families, cyathostomins are known to resist two of them. In order to counteract the development of such resistances, it is important to change deworming practices by adopting faecal egg count as a determining element whether or not to worm. Sustainable deworming could also include the implementation of management measures in order to reduce the parasitic pressure on pastures [2]. Nevertheless, literature provides very little data

#### **Chapter 10**

*Equine Science*

[31] Spencer NJ, Hu H. Enteric nervous system: Sensory transduction, neural circuits and gastrointestinal motility. Nature Reviews Gastroenterology &

morphological alterations, and possible means to prolong its physiological activity. In: Thymus. London, UK:

[41] Spahn TW, Kucharzik T. Modulating the intestinal immune system: The role of lymphotoxin and GALT organs. Gut.

IntechOpen Ltd; 2020

2004;**53**(3):456-465

polypeptides in submandibular glands. The Journal of Histochemistry and Cytochemistry. 1980;**28**(8):836-859

[33] Zhang W, Mei N, Qian L, Xie X, Fan Y, Zhao H, et al. Comparison of nutrients between donkey liver and pig liver, chicken liver and goose liver. Journal of Food Safety and Quality.

Hepatology. 2020;**17**:338-351

2018;**9**(16):4435-4439

[34] Sikandar A, Cheema AH, Younus M, Zaneb H. *Mycobacterium avium* subspecies paratuberculosis multibacillary infection (Johne's disease) in at teddy goat. Pakistan Veterinary Journal. 2012;**33**(2):260-262

[35] König HE, Liebich HG, editors. Veterinary Anatomy of Domestic Mammals: Textbook and Colour Atlas. New York: Schattauer Verlag; 2013

[36] Eurell JN, Frappier BL. Textbook of Veterinary Histology. 6th ed. USA:

[37] Karakurum E, Dursun N. Arterial vascularisation of liver and spleen in donkey (*Equus asinus* L.). Sağlık Bilimleri Veteriner Dergisi, Fırat Üniversitesi. 2014;**28**(2):73-76

[38] Frandson RD, Wilke WL, Fails AD. Anatomy and Physiology of Farm Animals. 7th ed. USA: Blackwell

[39] Sikandar A. Histopathology: An old yet important technique in modern science. In: Histopathology—An Update. IntechOpen; 2018

Microarchitecture of the thymus gland;

Blackwell Publishing; 2006

Publishing; 2009

[40] Sikandar A, Ullah N.

its age and disease-associated

[32] Barka T. Biologically active

**184**

## Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture' Programme

*Pauline Doligez, Marie Delerue, Agnès Orsoni, Bathilde Diligeon, Céline Saillet, Hervé Feugère, Guillaume Mathieu, Jean Baptiste Quillet and Stéphanie Cassigneul*

#### **Abstract**

The Équipâture programme examined the grazing regimes and parasite statuses of horses on 12 study farms. Its research yielded useful results. Rotational grazing of mares, foals, and school riding horses allowed animals to meet their nutritional needs without any supplements (50 ares/LU in the spring; 80 ares/LU in the summer). During the winter, haylage met the high demands of mares and foals. Late-cut hay could not, and there was a risk of P, Cu, and Zn deficiencies when horses were given a 100% hay diet. A sustainable approach to deworming was implemented on the farms. Based on faecal analysis, animals were assigned a parasite excretion status. As a result of this categorisation, only half of the animals were dewormed. This method helped limit deworming costs and the development of parasite resistance to dewormers.

**Keywords:** horse grazing, stocking rate, hay, haylage grass analysis, deworming, faecal egg count

#### **1. Introduction**

Grass, although being the most adapted food and considered as the least costly for herbivores, is nevertheless not always duly promoted in equine diets. The lack of data on equine pasture management and systematic deworming practices are recorded as factors hampering the efficient and sustainable management of grazing horses [1]. Systematic and frequent deworming of horses encourages the development of parasite resistance to dewormers. Three active dewormer families against cyathostomins, the most prevalent parasite in adult horses, are currently available on the market in France. Among the said three families, cyathostomins are known to resist two of them. In order to counteract the development of such resistances, it is important to change deworming practices by adopting faecal egg count as a determining element whether or not to worm. Sustainable deworming could also include the implementation of management measures in order to reduce the parasitic pressure on pastures [2]. Nevertheless, literature provides very little data

in this regard. In this context, the 'équipâture' programme was initiated through the monitoring of 12 equine study farms located in the regions of Centre Val de Loire, Limousin and Normandy (France) between 2016 and 2017, with the aim of analysing pasture management, promotion of forage intake, and implementation of sustainable deworming. In collaboration with Agricultural Chambers, local Horse Councils, and the French Horse and Equestrian Institute (IFCE), this study has permitted the compilation of data on horse grazing and pasture management. This summary illustrates the technical results of feed and pasture management, as well as the monitoring of animal infection.

#### **2. Material and methods**

At the national level, 12 study farms were monitored for over 2 years—2016 and 2017 (grazing seasons and in the winter). The selected equine farms were chosen according to the different breeds (draft horses, racehorses, sport and leisure horses, and cattle-combined) and the category of horses at grass (breeding stock and adult horses at rest or for schooling). The idea was to study and monitor a panel of structures with different production targets, using all grass surfaces for equine feeding and wishing to engage in more sustainable parasitic management practices. The 12 farms were located in 3 abundant grass regions [Centre-Val de Loire (4), Limousin (4), and Normandy (4)] and were comprised of 7 stud farms (2 draft horse + suckling-cow farmers, 1 pony breeder + crop farmer, 1 thoroughbred stud, 1 French Trotter stud, and 2 sport-horse breeders) and 5 riding establishments (1 riding school + sport-horse breeder, 2 riding schools + livery + breeder, 1 trail-riding centre, and 1 'active stall').

Batches of 10 to 25 adults (aged 3 years or more in 2016) per farm, i.e., 204 horses in total, were monitored by the study team (2 persons) with the aim of defining their parasitic status, measuring their body condition score (BCS), and analysing their feed pattern and grazing during the two 2016–2017 seasons. Since it has been illustrated that acquired immunity against cyathostomins is reached at age 3, adults can be grouped according to their strongyle egg excretion level. It is considered that 15 to 30% of horses over the age of 3 are responsible for excreting approximately 80% of all eggs [2].

#### **2.1 Monitoring animals**

For each animal over the two-year period, faeces were collected individually and their body condition score (BCS) and weight were recorded at three intervals (May, August, and November). Faecal sample, upon individual identification, was despatched within 24–48 hours after refrigeration to the same county veterinary analysis laboratory for faecal egg count [quantitative numeration of the number of strongyle and tapeworm eggs per gram of faeces (epg)]. For each visit, the INRA 1997 [3] grid was used to evaluate the body condition score of each monitored horse (score ranging from 0 to 5, 3 being the optimum score). The faecal egg count (FEC) results and BCS figures were regularly transmitted to the farmers, along with personal advice per animal as to whether or not to worm, in addition to guidance on feed and grazing.

In spring and summer, only horses whose faecal egg count resulted in an egg count exceeding 200 epg were dewormed with, respectively, ivermectin in spring and pyrantel in summer (such threshold being traditionally recommended in literature, according to [2]). All of the horses, regardless of the faecal egg count results, were dewormed at the end of autumn using a molecule association (moxidectin and praziquantel), thus enabling to eliminate strongyles, whether adult or larvae, as well as tapeworm.

**187**

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'…*

At each farm visit, some horses were absent or gone definitely (sold, owners changed, died, etc.); that is why, 6 (FEC + BCS) data/horse were not possible to

Three to four visits over the two-year period, from March to September, were conducted in order to draw up a grazing programme, evaluate pasture management, and carry out grass and fodder sampling. At the beginning of the season, the grazing forecast was estimated using the 'prév'Her' application (tool devised by the Creuse Chamber of Agriculture and adapted to take account of French equine LU references: one saddle mare and its foal = 1.2 LU [4–6]). The grazing base area for each batch was calculated for horses under rotational grazing. Forage, hay, and haylage samples over the 2 years, in addition to fresh grass samples in 2017, were taken from the grazing plots at various intervals, and they were tested using near-infrared spectrophotometry at the LANO 50 agronomy laboratory in order to determine their nutritive values [HFU/kg DM (net energy horse feed units), INRA 2011, (g HDCP) horse digestible crude proteins g/kgDM, Ca, P, K, Na in g/kg DM and Mg, Cu, Zn, Mn, Fe in mg/kg DM (XLStat statistics' analysis, Student Test)]. From 2 to 11 dried forage samples (2016 and 2017) were collected depending on the numbers of hay or haylage harvests per farm. From 2 to 6 fresh grass samples per farm (2017) depending on the numbers of grazing cycle exploited were taken across the various seasons from the grazed areas (rough areas excluded) on the same plots of permanent pastures, free of nitrogen fertiliser. Winter diets for the different equine categories were calculated with INRA system according to the nutritional values collected from the analysis of

**2.3 Influence of stud management and the age of the horses on parasite** 

• Foals (< 1 year) on site: two criteria—present or absent

turned out daily (stable/pasture combined)

and 15 years), and old (over 15 years)

Only the results of the faecal egg counts gathered in spring and summer of 2016 and 2017 were used. Indeed, studies have shown that parasites lay fewer eggs outside the grazing season, i.e., when the climate is less favourable to parasitical transmission [7]. Nevertheless, any such faecal egg count in November remains interesting in practice, in order to give an overall picture of the farm's parasitical

Five explanatory variables were retained in relation to stud management and to

• Accommodation type: two criteria—horses living out at pasture 24/7 or horses

• Annual stocking rates: three criteria—low (less than 0.6 LU/ha), medium (between 0.6 and 1.0 LU/ha), and high (more than 1 LU/ha), (LU: livestock

• Age of horses: three criteria—young (under 10 years), medium (between 10

• Significant movement on site: two criteria—few or many new arrivals

*DOI: http://dx.doi.org/10.5772/intechopen.92734*

**2.2 Monitoring the feed pattern and grazing**

collect over the 2 years.

forage harvested in 2016.

situation at the end of the grazing season.

**excretion**

the age of the horses:

unit)

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'… DOI: http://dx.doi.org/10.5772/intechopen.92734*

At each farm visit, some horses were absent or gone definitely (sold, owners changed, died, etc.); that is why, 6 (FEC + BCS) data/horse were not possible to collect over the 2 years.

#### **2.2 Monitoring the feed pattern and grazing**

*Equine Science*

as the monitoring of animal infection.

breeder, 1 trail-riding centre, and 1 'active stall').

approximately 80% of all eggs [2].

**2.1 Monitoring animals**

**2. Material and methods**

in this regard. In this context, the 'équipâture' programme was initiated through the monitoring of 12 equine study farms located in the regions of Centre Val de Loire, Limousin and Normandy (France) between 2016 and 2017, with the aim of analysing pasture management, promotion of forage intake, and implementation of sustainable deworming. In collaboration with Agricultural Chambers, local Horse Councils, and the French Horse and Equestrian Institute (IFCE), this study has permitted the compilation of data on horse grazing and pasture management. This summary illustrates the technical results of feed and pasture management, as well

At the national level, 12 study farms were monitored for over 2 years—2016 and 2017 (grazing seasons and in the winter). The selected equine farms were chosen according to the different breeds (draft horses, racehorses, sport and leisure horses, and cattle-combined) and the category of horses at grass (breeding stock and adult horses at rest or for schooling). The idea was to study and monitor a panel of structures with different production targets, using all grass surfaces for equine feeding and wishing to engage in more sustainable parasitic management practices. The 12 farms were located in 3 abundant grass regions [Centre-Val de Loire (4), Limousin (4), and Normandy (4)] and were comprised of 7 stud farms (2 draft horse + suckling-cow farmers, 1 pony breeder + crop farmer, 1 thoroughbred stud, 1 French Trotter stud, and 2 sport-horse breeders) and 5 riding establishments (1 riding school + sport-horse breeder, 2 riding schools + livery +

Batches of 10 to 25 adults (aged 3 years or more in 2016) per farm, i.e., 204 horses in total, were monitored by the study team (2 persons) with the aim of defining their parasitic status, measuring their body condition score (BCS), and analysing their feed pattern and grazing during the two 2016–2017 seasons. Since it has been illustrated that acquired immunity against cyathostomins is reached at age 3, adults can be grouped according to their strongyle egg excretion level. It is considered that 15 to 30% of horses over the age of 3 are responsible for excreting

For each animal over the two-year period, faeces were collected individually and their body condition score (BCS) and weight were recorded at three intervals (May, August, and November). Faecal sample, upon individual identification, was despatched within 24–48 hours after refrigeration to the same county veterinary analysis laboratory for faecal egg count [quantitative numeration of the number of strongyle and tapeworm eggs per gram of faeces (epg)]. For each visit, the INRA 1997 [3] grid was used to evaluate the body condition score of each monitored horse (score ranging from 0 to 5, 3 being the optimum score). The faecal egg count (FEC) results and BCS figures were regularly transmitted to the farmers, along with personal advice per animal as to whether or not to worm, in addition to guidance on feed and grazing.

In spring and summer, only horses whose faecal egg count resulted in an egg count exceeding 200 epg were dewormed with, respectively, ivermectin in spring and pyrantel in summer (such threshold being traditionally recommended in literature, according to [2]). All of the horses, regardless of the faecal egg count results, were dewormed at the end of autumn using a molecule association (moxidectin and praziquantel), thus

enabling to eliminate strongyles, whether adult or larvae, as well as tapeworm.

**186**

Three to four visits over the two-year period, from March to September, were conducted in order to draw up a grazing programme, evaluate pasture management, and carry out grass and fodder sampling. At the beginning of the season, the grazing forecast was estimated using the 'prév'Her' application (tool devised by the Creuse Chamber of Agriculture and adapted to take account of French equine LU references: one saddle mare and its foal = 1.2 LU [4–6]). The grazing base area for each batch was calculated for horses under rotational grazing. Forage, hay, and haylage samples over the 2 years, in addition to fresh grass samples in 2017, were taken from the grazing plots at various intervals, and they were tested using near-infrared spectrophotometry at the LANO 50 agronomy laboratory in order to determine their nutritive values [HFU/kg DM (net energy horse feed units), INRA 2011, (g HDCP) horse digestible crude proteins g/kgDM, Ca, P, K, Na in g/kg DM and Mg, Cu, Zn, Mn, Fe in mg/kg DM (XLStat statistics' analysis, Student Test)]. From 2 to 11 dried forage samples (2016 and 2017) were collected depending on the numbers of hay or haylage harvests per farm. From 2 to 6 fresh grass samples per farm (2017) depending on the numbers of grazing cycle exploited were taken across the various seasons from the grazed areas (rough areas excluded) on the same plots of permanent pastures, free of nitrogen fertiliser. Winter diets for the different equine categories were calculated with INRA system according to the nutritional values collected from the analysis of forage harvested in 2016.

#### **2.3 Influence of stud management and the age of the horses on parasite excretion**

Only the results of the faecal egg counts gathered in spring and summer of 2016 and 2017 were used. Indeed, studies have shown that parasites lay fewer eggs outside the grazing season, i.e., when the climate is less favourable to parasitical transmission [7]. Nevertheless, any such faecal egg count in November remains interesting in practice, in order to give an overall picture of the farm's parasitical situation at the end of the grazing season.

Five explanatory variables were retained in relation to stud management and to the age of the horses:


Among the 204 horses monitored, data from 83 horses were used for the analysis, the result range of the others being incomplete. For the horses used, five explanatory variables were applied in addition to the 2016 and 2017 spring and summer faecal egg count results. The five explanatory variables underwent a multiple correspondence analysis (R software), followed by agglomerative clustering (AHC), in order to compile groups of variable criteria. The clusters derived from the AHC are those that maximise the difference of one group in relation to another, while ensuring the best homogeneity among individuals within the same group. The best division singles out four groups:


A principal component analysis (PCA) was conducted in order to observe a possible influence of the explanatory variables on parasite excretion in the spring and summer of 2016 and 2017.

#### **3. Results of the feed patterns and pasture management**

#### **3.1 Stud farm stocking rates**

The indicator retained for evaluating the stocking rate is calculated according to the number of LU (livestock units) per equine equivalent (one saddle mare and its foal = 1.2 LU, INRA 2012) in relation to the volume of the breed main forage areas (MFAs) in hectares. The 12 stud farms monitored are characterised by a medium to low stocking rate (from 1.05 to 0.6 LU/ha of MFA), on par with the data of equine farms monitored in the context of the REFErences' network (7). The most intensive systems can be found in multi-production farms, comprising horse breeding alongside another production (beef cattle or crop farming). The most extensive farms (<0.5 LU/ha of MFA) breed exclusively top pedigree horses (2/12). For such farms, the productivity of grassland is not a priority when considering the real economic value of the animals [8].

#### **3.2 Stocking rate and conditions of pasture management**

Pasture management for the 33 batches of animals was duly monitored on the 12 study farms. Grazing rotations were recorded by noting the number of animals present per cycle.

Pasture management was split into three different types (**Table 1**).

Seven batches of horses monitored out of 33 (21%) were reared in rotational pastures with a stocking rate comprised between 40 and 60 ares/LU in spring and 80 ares/LU in summer. Sixty per cent of the farms mulched the herbage rejected by the animals.

**189**

nor even in winter.

**3.4 Grass analysis**

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'…*

4/33 (12%) Stabled horses

7/33 (21%) Broodmares and

22/33 (67%) Horses at rest

Horses at rest

foals School horses

Broodmares

**Horse types Feed pattern and pasture** 

**management**

The so-called paddock void of feeding role several hours/day for exercise 24/7 for overweight horses with restricted forage rations

Rotational grazing

Grazing 24/7

**No. of batches of horses observed and overall %**

*For example:* 14 thoroughbred yearlings and 10 cows with calf at foot were taken in the spring to a 9-ha pasture divided into 5 separate plots of 1.5 to 2 ha. This

Among 2/3 of the batches (67%), grazing 24/7 is generally conducted at low intensity (>100 ares/LU) across large areas, with small batches of horses (2 to 3) given extra fodder in summer and/or autumn [9]. Rough was mulched several times

To end, for 12% of the batches, small surface areas (<0.2 ha), mainly located near the farm buildings, were used as 'exercise paddocks' for stabled horses. Such paddocks may also serve to accommodate horses that should have limited grazing (overweight horses and ponies at rest or retired). These paddocks are not considered

A body condition score (BCS) was recorded for 132 adult horses at three separate

The BCS of the school horses was >3.6 for 48% of them in spring and 39% in summer. In autumn, they gained weight with 16% becoming quite overweight (BCS > 4.1). In such a case, forage supplementation in winter was delayed. Eightythree per cent of the horses at rest were overweight (BCS > 3.6) in summer, 37% of which showed a BCS > 4.1. Grass restrictions were imposed on certain horses (BCS > 4.6 in summer) by placing them in drylots in order to limit the risk of laminitis. Fifty per cent of the retired horses with a BCS < 2.4 in summer were at least supplemented in forage. Twenty-nine per cent of the thoroughbred broodmares, some of which being supplemented with concentrates, became overweight in autumn (BCS > 3.6). Eighty-eight per cent of draft horse broodmares that attained a BCS > 4.6 in autumn were not given extra fodder during that period,

The mean HFU energy value of grass was exactly the same in April and in May (0.718 vs. 0.72 HFU/kg DM). In June, the mean energy value significantly dropped

*DOI: http://dx.doi.org/10.5772/intechopen.92734*

**Stocking rate observed**

summer

spring

**Table 1.**

<20 ares/LU in spring/

40–60 ares/LU in

> 100 ares/LU in spring and summer

80 ares/LU in summer

combined batch then grazed 18 ha in the summer.

*Stocking rate observed and management conditions on the 12 study farms.*

during the grazing season.

as a nutritional source for the animals.

**3.3 Estimation of a horse's body condition**

intervals (May, August, and November) over the 2 years.

*3.4.1 HFU content and digestible crude proteins/kg fresh grass DM*

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'… DOI: http://dx.doi.org/10.5772/intechopen.92734*


#### **Table 1.**

*Equine Science*

best division singles out four groups:

• Group 2: horses over the age of 16

arrivals, living out 24/7, and horses aged under 10)

foals, low or medium stocking rate, and few new arrivals)

**3. Results of the feed patterns and pasture management**

**3.2 Stocking rate and conditions of pasture management**

15 years)

summer of 2016 and 2017.

**3.1 Stud farm stocking rates**

value of the animals [8].

present per cycle.

the animals.

Among the 204 horses monitored, data from 83 horses were used for the analysis, the result range of the others being incomplete. For the horses used, five explanatory variables were applied in addition to the 2016 and 2017 spring and summer faecal egg count results. The five explanatory variables underwent a multiple correspondence analysis (R software), followed by agglomerative clustering (AHC), in order to compile groups of variable criteria. The clusters derived from the AHC are those that maximise the difference of one group in relation to another, while ensuring the best homogeneity among individuals within the same group. The

• Group 1: stud farms with a high turnover (many new arrivals, high stocking rate, presence of foals, living out 24/7, and horses mostly aged between 10 and

• Group 3: riding establishments with a low turnover (absence of foals, few new

• Group 4: stud farms with a low turnover (horses turned out daily, presence of

A principal component analysis (PCA) was conducted in order to observe a possible influence of the explanatory variables on parasite excretion in the spring and

The indicator retained for evaluating the stocking rate is calculated according to the number of LU (livestock units) per equine equivalent (one saddle mare and its foal = 1.2 LU, INRA 2012) in relation to the volume of the breed main forage areas (MFAs) in hectares. The 12 stud farms monitored are characterised by a medium to low stocking rate (from 1.05 to 0.6 LU/ha of MFA), on par with the data of equine farms monitored in the context of the REFErences' network (7). The most intensive systems can be found in multi-production farms, comprising horse breeding alongside another production (beef cattle or crop farming). The most extensive farms (<0.5 LU/ha of MFA) breed exclusively top pedigree horses (2/12). For such farms, the productivity of grassland is not a priority when considering the real economic

Pasture management for the 33 batches of animals was duly monitored on the 12 study farms. Grazing rotations were recorded by noting the number of animals

Seven batches of horses monitored out of 33 (21%) were reared in rotational pastures with a stocking rate comprised between 40 and 60 ares/LU in spring and 80 ares/LU in summer. Sixty per cent of the farms mulched the herbage rejected by

Pasture management was split into three different types (**Table 1**).

**188**

*Stocking rate observed and management conditions on the 12 study farms.*

*For example:* 14 thoroughbred yearlings and 10 cows with calf at foot were taken in the spring to a 9-ha pasture divided into 5 separate plots of 1.5 to 2 ha. This combined batch then grazed 18 ha in the summer.

Among 2/3 of the batches (67%), grazing 24/7 is generally conducted at low intensity (>100 ares/LU) across large areas, with small batches of horses (2 to 3) given extra fodder in summer and/or autumn [9]. Rough was mulched several times during the grazing season.

To end, for 12% of the batches, small surface areas (<0.2 ha), mainly located near the farm buildings, were used as 'exercise paddocks' for stabled horses. Such paddocks may also serve to accommodate horses that should have limited grazing (overweight horses and ponies at rest or retired). These paddocks are not considered as a nutritional source for the animals.

#### **3.3 Estimation of a horse's body condition**

A body condition score (BCS) was recorded for 132 adult horses at three separate intervals (May, August, and November) over the 2 years.

The BCS of the school horses was >3.6 for 48% of them in spring and 39% in summer. In autumn, they gained weight with 16% becoming quite overweight (BCS > 4.1). In such a case, forage supplementation in winter was delayed. Eightythree per cent of the horses at rest were overweight (BCS > 3.6) in summer, 37% of which showed a BCS > 4.1. Grass restrictions were imposed on certain horses (BCS > 4.6 in summer) by placing them in drylots in order to limit the risk of laminitis. Fifty per cent of the retired horses with a BCS < 2.4 in summer were at least supplemented in forage. Twenty-nine per cent of the thoroughbred broodmares, some of which being supplemented with concentrates, became overweight in autumn (BCS > 3.6). Eighty-eight per cent of draft horse broodmares that attained a BCS > 4.6 in autumn were not given extra fodder during that period, nor even in winter.

#### **3.4 Grass analysis**

#### *3.4.1 HFU content and digestible crude proteins/kg fresh grass DM*

The mean HFU energy value of grass was exactly the same in April and in May (0.718 vs. 0.72 HFU/kg DM). In June, the mean energy value significantly dropped to 0.67 HFU/kg DM (p < 0.01), proving to be more heterogeneous, and then increased again in July to 0.71 HFU/kg DM (p < 0.01). The higher energy values in July were due to regrowth following a more prominent period of rain than in June 2017 (**Figure 1**). Hence, other mean grass HFU comparisons in April and May among the three regions illustrated superior energy values in Normandy by +0.04 (p < 0.01) and +0.06 (p < 0.01) HFU points, respectively, in relation to the HFU value of grass in the Limousin and the region of Centre Val de Loire.

Concerning the protein values in gr HDCP/kg DM (**Figure 2**), the averages observed during the grazing season hardly differed (p > 0.5) on a monthly scale. Hence, the protein value comparisons among the three regions failed to show any difference (p > 0.5).

When grass was abundant and could be compared with a minimal to maximal *ad lib* intake level of DM/kg, the nutritional needs (in intake HFU and gr HDCP/ kg DM) of the broodmare during the 1st month of suckling and of the 18-month yearling are basically covered between April and June across the three regions.

#### **3.5 Analysis of the harvested dry forage and the consequences on winter diets (HFU and g HDCP/kg DM)**

#### *3.5.1 Energy and protein*

The harvesting conditions in 2016 (late first cut in July) resulted in slightly lower energy and crude protein values by, respectively, 0.04 points HFU and 8 g HDCP/ kg of DM in relation to the values of forage harvested in 2017 (early to mid-June cut) (**Table 2**).

The HFU and HDCP nutritive values of 62 hay and 10 haylage samples were compared with the recommended dietary needs [4] for three categories of animals receiving essentially forage-based rations in winter (**Table 3**).

Haylage harvested at the end of May or as second cut seems better adapted than hay for animals with high nutritional needs (broodmares and foals). For horses at rest or having light exercise, hay seems more adapted despite a 5- to 15-gr HDCP/kg DM crude protein deficiency in relation to dietary needs (**Table 3**).

#### **Figure 1.**

*Net energy values (net energy horse feed units: HFU/kg DM) of grass samples depending on grazing period (2017 season, n = 52).*

**191**

forage analysis.

**Table 2.**

**Figure 2.**

*season, n = 52).*

*3.5.2 Minerals*

at rest was far too rich (**Table 4**).

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'…*

For each stud farm, a report on the winter rations was drawn up based on the

*Nutritional values (HFU and g HDCP) of hay depending on harvest year.*

*Horse digestible crude protein values (g HDCP/kg DM) of grass samples depending on grazing period (2017* 

**2016 (n = 40), 2017 (n = 22) 2016 2017 2016 2017** Minimum 0.33 0.38 12 16 Maximum 0.65 0.62 76 73 **Averages 0.48 0.52 25 33** Standard deviation 0.07 0.06 13 14

**HFU/kg DM g HDCP/kg DM**

+ 0.04 p < 0.1 +8 p < 0.1

If the net energy and digestible crude protein needs of animals with high nutritional needs (broodmares) are covered by haylage-based rations, those based on hay harvested in 2016 (with or without concentrates) fail to cover such needs (**Table 4**). For animals with minimal needs (horse at rest or in light exercise), a winter ration of 100% hay, or 90% hay +10% cereals, based on forage analysed in 2016, failed to cover the digestible crude protein needs. A 100% haylage ration for a horse

The Ca and Mg content of the three forage types (grass, haylage, and hay) (**Table 5**) covered the overall daily needs for the three animal types (broodmare, 18-month foal, and horse at rest or in light exercise). The mean phosphorus content of the hay (Me = 1.8 g/kg DM) was deficient for animals with high nutritional needs (broodmare: 3.2–4.3 g/kg DM; 18-month foal: 2.7–3.4 g/kg DM). The Ca/P calciumphosphate ratio showed an average of 2 instead of 1.5 (mean reference of all horse categories [4]). The potassium content was in excess in relation to needs (**Table 5**).

*DOI: http://dx.doi.org/10.5772/intechopen.92734*

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'… DOI: http://dx.doi.org/10.5772/intechopen.92734*

#### **Figure 2.**

*Equine Science*

difference (p > 0.5).

*3.5.1 Energy and protein*

cut) (**Table 2**).

**(HFU and g HDCP/kg DM)**

to 0.67 HFU/kg DM (p < 0.01), proving to be more heterogeneous, and then increased again in July to 0.71 HFU/kg DM (p < 0.01). The higher energy values in July were due to regrowth following a more prominent period of rain than in June 2017 (**Figure 1**). Hence, other mean grass HFU comparisons in April and May among the three regions illustrated superior energy values in Normandy by +0.04 (p < 0.01) and +0.06 (p < 0.01) HFU points, respectively, in relation to the HFU

Concerning the protein values in gr HDCP/kg DM (**Figure 2**), the averages observed during the grazing season hardly differed (p > 0.5) on a monthly scale. Hence, the protein value comparisons among the three regions failed to show any

When grass was abundant and could be compared with a minimal to maximal *ad lib* intake level of DM/kg, the nutritional needs (in intake HFU and gr HDCP/ kg DM) of the broodmare during the 1st month of suckling and of the 18-month yearling are basically covered between April and June across the three regions.

**3.5 Analysis of the harvested dry forage and the consequences on winter diets** 

The harvesting conditions in 2016 (late first cut in July) resulted in slightly lower energy and crude protein values by, respectively, 0.04 points HFU and 8 g HDCP/ kg of DM in relation to the values of forage harvested in 2017 (early to mid-June

The HFU and HDCP nutritive values of 62 hay and 10 haylage samples were compared with the recommended dietary needs [4] for three categories of animals

*Net energy values (net energy horse feed units: HFU/kg DM) of grass samples depending on grazing period* 

Haylage harvested at the end of May or as second cut seems better adapted than hay for animals with high nutritional needs (broodmares and foals). For horses at rest or having light exercise, hay seems more adapted despite a 5- to 15-gr HDCP/kg

receiving essentially forage-based rations in winter (**Table 3**).

DM crude protein deficiency in relation to dietary needs (**Table 3**).

value of grass in the Limousin and the region of Centre Val de Loire.

**190**

**Figure 1.**

*(2017 season, n = 52).*

*Horse digestible crude protein values (g HDCP/kg DM) of grass samples depending on grazing period (2017 season, n = 52).*


#### **Table 2.**

*Nutritional values (HFU and g HDCP) of hay depending on harvest year.*

For each stud farm, a report on the winter rations was drawn up based on the forage analysis.

If the net energy and digestible crude protein needs of animals with high nutritional needs (broodmares) are covered by haylage-based rations, those based on hay harvested in 2016 (with or without concentrates) fail to cover such needs (**Table 4**).

For animals with minimal needs (horse at rest or in light exercise), a winter ration of 100% hay, or 90% hay +10% cereals, based on forage analysed in 2016, failed to cover the digestible crude protein needs. A 100% haylage ration for a horse at rest was far too rich (**Table 4**).

#### *3.5.2 Minerals*

The Ca and Mg content of the three forage types (grass, haylage, and hay) (**Table 5**) covered the overall daily needs for the three animal types (broodmare, 18-month foal, and horse at rest or in light exercise). The mean phosphorus content of the hay (Me = 1.8 g/kg DM) was deficient for animals with high nutritional needs (broodmare: 3.2–4.3 g/kg DM; 18-month foal: 2.7–3.4 g/kg DM). The Ca/P calciumphosphate ratio showed an average of 2 instead of 1.5 (mean reference of all horse categories [4]). The potassium content was in excess in relation to needs (**Table 5**).


#### **Table 3.**

*Nutritional values (HFU and g HDCP) of hay and haylage compared with the animals' dietary needs.*


#### **Table 4.**

*Winter rations calculated according to the nutritional values of forage harvested in 2016.*

#### *3.5.3 Trace minerals*

If the Cu and Zn content was deficient for all forages, the manganese and iron content was significantly in excess (**Table 5**). Among the stud farms monitored, some administered mineral and vitamin supplementation to the winter diet (5/12) or make it available in the grazing period (3/12).

#### **4. Results of parasite excretion monitoring**

Throughout the grazing season (spring and summer 2016 and 2017; **Figure 3**), the results of the faecal egg counts carried out on the 83 adult horses (**Table 6**) aged over 3 enabled, on average, to simply worm 50% of the horses, i.e., those excreting more than 200 epg. Such horses are nevertheless responsible for excreting 94 to 99% of the eggs, depending on the period concerned, thus significantly contributing to pasture contamination.

#### **4.1 Definition of the excretory status**

Three excretory statuses of horses were defined:

• 23% of the horses have a low excretory status: horses excreting less than 200 epg in all faecal egg count analysed in spring and summer of 2016/2017.

**193**

**Figure 3.**

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'…*

**Median σ Median σ Median σ**

Ca (g) 6.2 1.9 6.4 1.4 4.0 1.1 2 at 5 g P (g) 2.9 0.6 2.9 0.3 **1.8** 0.5 1.7 at 4.3 g Ca/P ratio **2.2** 0.9 **2.1** 0.6 **2.2** 0.9 1.35 at 1.8 Mg (g) 1.7 0.4 1.5 0.5 1.3 0.3 0.7 at 1.1 g K (g) **23.8** 5.5 **25.1** 6.5 **14.6** 4.6 2.5 at 5.5 g Na (g) 0.8 0.8 0.7 1.4 1.2 1.5 0.9 at 2 g Cu (mg) **5.5** 1.6 **4.9** 1.3 **3.2** 1.1 10 mg Zn (mg) **23.9** 7.6 **25.0** 6.2 **17.9** 5.2 50 mg

Mn (mg) **155.2** 120.1 **195.3** 86.6 **158.1** 150.6 40 mg Fe (mg) **147.6** 215.3 **152.5** 94.8 **116.6** 507.0 50 at 80 mg

*Mineral content in gr or mg/kg DM of forage (grass, haylage, and hay) for the 2 years 2016 and 2017. Data over* 

0.2 0.1 0.2 0.1 0.2 0.1 0.2

**Grass (n = 53) Haylage (n = 10) Hay (n = 62) Early pregnant** 

**mare, 18–24 month yearling and light exercise adult average needs [4], per g or mg per kg DM intake**

• 13% of the horses have a high excretory status: horses excreting more than 200 epg in all faecal egg count analysed in spring and summer of 2016/2017.

*Percentage of the 83 horses excreting more or less 200 strongyle epg at each faecal egg count (FEC).*

• 64% of the horses have an unstable excretory status: horses excreting alterna-

tively more than 200 epg or less than 200 epg.

*DOI: http://dx.doi.org/10.5772/intechopen.92734*

**Mineral g/kg DM and trace minerals mg/kg DM from forages**

Cu/Zn ratio

**Table 5.**

*or under the average needs.*

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'… DOI: http://dx.doi.org/10.5772/intechopen.92734*


#### **Table 5.**

*Equine Science*

(n = 10)

Energy and protein values/kg DM of hays (n = 62) and haylage

Daily needs/kg DM according to horse's low and high intake

**192**

*3.5.3 Trace minerals*

**Table 4.**

**Table 3.**

ing to pasture contamination.

**4.1 Definition of the excretory status**

or make it available in the grazing period (3/12).

Haylage (87%) + industrial concentrates (13%) 92 120

Standard deviation

9th month pregnant mare

18–24 month yearling

Adults at rest or having light exercise

*Winter rations calculated according to the nutritional values of forage harvested in 2016.*

**% of net energy and protein needs covered by the four ration types observed (/kg DM)**

**4. Results of parasite excretion monitoring**

Three excretory statuses of horses were defined:

If the Cu and Zn content was deficient for all forages, the manganese and iron content was significantly in excess (**Table 5**). Among the stud farms monitored, some administered mineral and vitamin supplementation to the winter diet (5/12)

100% hay 80 50 98 70 Hay (90%) + cereals (10%) 110 50 133 70 100% haylage 174 194

*Nutritional values (HFU and g HDCP) of hay and haylage compared with the animals' dietary needs.*

**Ninth month pregnant mare**

> **in g HDCP**

**HFU/kg DM g HDCP/kg DM Haylage Hay Haylage Hay**

0.04 0.07 12 13

**0.55–0.67 43–54**

**0.58–0.73 33–41**

**0.46–0.60 33–43**

Minimum 0.62 0.33 35.2 11.8 Maximum 0.73 0.65 76.8 75.9 **Averages 0**.**67 0**.**49 55 28**

P-value +0.18 (p < 0.01) +27 (p < 0.01)

**in HFU** **Adult at rest or in light exercise**

**in HFU in g HDCP**

Throughout the grazing season (spring and summer 2016 and 2017; **Figure 3**), the results of the faecal egg counts carried out on the 83 adult horses (**Table 6**) aged over 3 enabled, on average, to simply worm 50% of the horses, i.e., those excreting more than 200 epg. Such horses are nevertheless responsible for excreting 94 to 99% of the eggs, depending on the period concerned, thus significantly contribut-

• 23% of the horses have a low excretory status: horses excreting less than 200 epg in all faecal egg count analysed in spring and summer of 2016/2017.

*Mineral content in gr or mg/kg DM of forage (grass, haylage, and hay) for the 2 years 2016 and 2017. Data over or under the average needs.*

#### **Figure 3.**

*Percentage of the 83 horses excreting more or less 200 strongyle epg at each faecal egg count (FEC).*



#### **Table 6.**

*Followed animals per farm distribution.*

#### **4.2 Study of the influence of stud management and horse's age on the level of equine parasitic excretion**

In the principal component analysis, four groups were identified:


The first and second axes of the PCA are those that best resume the data contained in the five variables; they are thus retained for the analysis. Axis 1 represents the general tendency of the faecal egg count (FEC) for an individual: on the left, an individual shows basically low results, while on the right, the results are generally high. Axis 2 represents the results from spring and summer 2016: at the top, the individuals show high results in spring 2016, while in summer 2016, the results are low. **Figure 4** thus enables to distinguish a high excretory profile in spring 2016 and a low excretory profile in summer 2016 (in the direction of 'FEC 1'), a high excretory profile in summer 2016 and a low excretory profile in spring 2016 (in the direction of 'FEC 2'), and a high excretory profile in 2016 and in 2017 (in the direction of 'FEC 4' and 'FEC 5').

**Figure 5**, on its part, enables to identify certain individuals belonging to one of the profiles highlighted in the graph of the variables. The individuals (grey dots) surrounded by a continuous line illustrate high FEC in spring 2016, though with low results in summer 2016. The individuals surrounded by a dotted line illustrate high FEC in summer 2016, though with low FEC in spring 2016. The individuals surrounded by dashes illustrate high FEC for all FEC. These different ellipses were hand drawn for educational purposes. All other individuals illustrate low or average FEC. The four groups of horses (black boxes), identified in accordance with their management type, appear in the box in the centre of the graph. None of these groups particularly stand out in relation to the four axes. No significant difference can be observed among the faecal egg count results for the different groups.

**195**

**5. Discussion**

*faecal egg count (FEC).*

**Figure 5.**

**Figure 4.**

**5.1 Stocking rate and pasture management**

The stud managements observed illustrated a very low stocking rate in spring, thereby requiring regular mechanical maintenance in order to limit the development of roughs. The management of certain batches of animals (mares with foal at foot to be covered by a stallion and requiring individual attention and school horses exercised daily) and the need for shelters and secure fencing entail extensive pasture management and 24/7 grazing, where manipulation and care take priority in relation to a sustainable management of grassland. Such low stocking rate is, for some batches, linked to the use of pastures for wintering horses, thus reducing the available grass stocks early in the season and the productivity of grasslands [9].

*Principal component analysis on the effect of the individuals on the results of spring and summer 2016 and 2017* 

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'…*

*Principal component analysis on the effect of the five explanatory variables on the results of spring and* 

*DOI: http://dx.doi.org/10.5772/intechopen.92734*

*summer 2016 and 2017 faecal egg count (FEC).*

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'… DOI: http://dx.doi.org/10.5772/intechopen.92734*

#### **Figure 4.**

*Equine Science*

Nb of followed animals with full FEC results in spring and summer 2016/2017

*\**

**Table 6.**

**4.2 Study of the influence of stud management and horse's age on the level** 

**Region Centre Val de Loire Normandie Limousin**

**Farm No. 1 2 3 4 5 6 7 8 9 10 11 12**

14 18 0\* 5 4 0\* 14 11 0\* 8 0\* 9

• Group 1: stud farms with a high turnover (many new arrivals, high stocking rate, presence of foals, living out 24/7, and horses mostly aged between 10 and

• Group 3: riding establishments with a low turnover (absence of foals, few new

• Group 4: stud farms with a low turnover (horses turned out daily, presence of

The first and second axes of the PCA are those that best resume the data contained in the five variables; they are thus retained for the analysis. Axis 1 represents the general tendency of the faecal egg count (FEC) for an individual: on the left, an individual shows basically low results, while on the right, the results are generally high. Axis 2 represents the results from spring and summer 2016: at the top, the individuals show high results in spring 2016, while in summer 2016, the results are low. **Figure 4** thus enables to distinguish a high excretory profile in spring 2016 and a low excretory profile in summer 2016 (in the direction of 'FEC 1'), a high excretory profile in summer 2016 and a low excretory profile in spring 2016 (in the direction of 'FEC 2'), and a high excretory profile in 2016 and in 2017 (in the direction of

**Figure 5**, on its part, enables to identify certain individuals belonging to one of the profiles highlighted in the graph of the variables. The individuals (grey dots) surrounded by a continuous line illustrate high FEC in spring 2016, though with low results in summer 2016. The individuals surrounded by a dotted line illustrate high FEC in summer 2016, though with low FEC in spring 2016. The individuals surrounded by dashes illustrate high FEC for all FEC. These different ellipses were hand drawn for educational purposes. All other individuals illustrate low or average FEC. The four groups of horses (black boxes), identified in accordance with their management type, appear in the box in the centre of the graph. None of these groups particularly stand out in relation to the four axes. No significant difference can be observed among the faecal egg count results for the

foals, low or medium stocking rate, and few new arrivals), 27 horses

In the principal component analysis, four groups were identified:

arrivals, living out 24/7, and horses aged under 10), 18 horses

**of equine parasitic excretion**

• Group 2: horses over the age of 16, 18 horses

15 years), 20 horses

*Horses with less than 6 FEC/2 years.*

*Followed animals per farm distribution.*

'FEC 4' and 'FEC 5').

**194**

different groups.

*Principal component analysis on the effect of the five explanatory variables on the results of spring and summer 2016 and 2017 faecal egg count (FEC).*

#### **Figure 5.**

*Principal component analysis on the effect of the individuals on the results of spring and summer 2016 and 2017 faecal egg count (FEC).*

#### **5. Discussion**

#### **5.1 Stocking rate and pasture management**

The stud managements observed illustrated a very low stocking rate in spring, thereby requiring regular mechanical maintenance in order to limit the development of roughs. The management of certain batches of animals (mares with foal at foot to be covered by a stallion and requiring individual attention and school horses exercised daily) and the need for shelters and secure fencing entail extensive pasture management and 24/7 grazing, where manipulation and care take priority in relation to a sustainable management of grassland. Such low stocking rate is, for some batches, linked to the use of pastures for wintering horses, thus reducing the available grass stocks early in the season and the productivity of grasslands [9].

When the stocking rate in the spring exceeds 100 ares/LU (22/33 of the batches studied), practices aiming to intensify the farming system, such as the sale of forage or taking on boarding cattle, were proposed to breeders. Nevertheless, the lack of human resources, the necessary investment in harvesting equipment, and additional infrastructures (fencing and wintering barn), as well as the lack of economic production attractiveness (suckling cows), are the main blockers exposed by the stud farms for developing other activities to enable optimum use of the grassland.

Since few references already exist on the interest of an equine-cattle grazing combination in grassy areas [6, 10], the French Horse and Equestrian Institute (IFCE) and the National Institute for Agricultural Research (INRA) are currently conducting studies in order to pinpoint its effects in relation to a farm's biotechnical, economic, and social (labour) performances [11].

Rotational grazing is considered as the most appropriate practice for providing an adequate energy and protein balance for animals requiring high nutritional needs (broodmares and foals), though without the necessity for concentrate supplementation and without body condition loss. The grass available must be of adequate quality (in leaf) and quantity (height between 5 and 20 cm) [12]. For those stud farms having thus invested, such practice should be long-lasting.

For horses at rest, their living conditions take priority over the optimum use of grassland. Pasture management thus becomes somewhat tricky when trying to prevent overweight and consequential metabolic illnesses (laminitis) in adult horses having little or no exercise. Indeed, as a monogastric herbivore, diets with a low starch and sugar content are more adapted to horses, who have the ability to continuously ingest vast quantities of rough forage in order to satisfy their nutritional needs and maintain a healthy digestive system [13]. When grass resources are abundant, ingestion increases beyond the normal capacity in terms of the nutritional needs for maintaining a 3/5 body condition score, and the lack of exercise results in weight gain. Restricting food in winter, in order to encourage weight loss and to limit overweight just prior to the grazing season, could be a solution. Nevertheless, such practice is scarcely applied by breeders, the latter generally offering ad libitum forage in winter.

In spring, the grass available in leaf can represent a far too rich food resource (in energy and proteins) with over 50% of the grass analysis attaining + 132% of the HDCP needs and + 110% of the HFU needs for such horses already in good condition (BCS > 3.6) at the end of winter.

Drylots are temporarily used for part of the day, or even 24/7, in order to restrict the food intake of overweight animals (horses and ponies) (body condition score corresponding to 4/5 at the end of winter). Low-protein fibrous forage is often administered in order to prevent metabolic illnesses (laminitis), notably when grass grows abundantly (spring, autumn). Such management raises the question of how to optimise the maintenance of such areas, not only in order to limit the propagation of weeds but also to maintain the weight-bearing ability of the ground in a manner not to damage the horses' hooves. An alternative, in order to prevent the degradation of drylots, sacrificed due to overgrazing, could be the creation of stabilised sandy areas where such horses could be parked during sensitive periods (spring, autumn).

#### **5.2 Analysis of forage and winter rations**

None of the stud farms monitored undertook forage analysis, nor calculated routine rations, despite the diet administered to their horses consisting of forage, for the most part. An essentially forage-predominant diet in terms of proportion

**197**

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'…*

HFU ratio) compared with diets consisting of haylage (90 HDCP/HFU ratio, significantly more in line with the needs of the horse). Nevertheless, few stud farms (2/12) produce haylage. Eighty-three per cent of the stud farms monitored do not produce such forage, either because they have no knowledge of the harvest techniques (4/12) or because such forage constitutes too richer feed in relation to their

and quantity, thus enabling to further reduce the amount of concentrates, would not only control feed costs but also promote digestive health and the overall wellbeing of the horse [14, 15]. A simulation of the feed costs on a farm enabled to illustrate that a ration consisting of haylage + hay results in savings of up to 25% in

Diets consisting of just hay, or hay + cereals, are often less balanced (~40 HDCP/

Adding a vitamin-mineral supplement (VMS) to the ration is not systematic. Having said that, P, Cu, and Zn deficiencies were recorded on the forage analysed. A vitamin-mineral supplement is necessary not only in winter rations but also

The implementation of targeted deworming above the threshold of 200 epg in such equestrian structures enabled to simply worm half of the adult horses present on site during the grazing season. Such 200 epg threshold thus enables to preserve a parasite population not subject to anthelminthic treatment, the so-called refuge population [2]. The larger the refuge population, the less rapidly resistances

Having said that, these dewormed horses were responsible for excreting more than 94% of eggs across the pastures. Targeted deworming thus enables to rupture the cycle of most parasites and hence to safeguard the health of all the horses on site. One of the main hindrances to implementing targeted deworming within a structure seems, aside from the time spent in collecting individual stools, to be its cost. Indeed, Sallé et al. [17] illustrated that such targeted deworming can be financially viable in relation to systematic deworming insofar as the cost of a faecal egg count is less than 5 Euros. In the stud farms monitored, approximately ¼ of the horses had a low excretory status. Literature shows that such low excretory status is stable from one grazing season to the next [18, 19], for a healthy horse accommodated in stable conditions. In this study, 90% of the horses with this status in 2016 had the same status in 2017. For such horses, deworming once or twice a year (in autumn and possibly in spring) was recommended, without annual faecal egg count testing; only one faecal egg count approximately every 2–3 years in order to verify that the on-site epidemiological situation has not evolved and that the horse has not changed status. Annual faecal egg count monitoring is moreover recommended in the case of suspicion of immune deficiency (senior horse over the age of 20 or

The cost of sustainable deworming could thus be reduced over the seasons due to the stability of the low excretory status requiring less strict faecal egg count. Having said that, the high excretory status was much less stable in between the two grazing seasons, since only 37% of the horses with such status in 2016 also had the same status in 2017, and the remaining 63% passed from a high excretory status to an unstable status. For such unstable and high excretory statuses, it was advised

to continue faecal egg count in order to adapt the frequency of deworming. In terms of faecal egg count results, the situations varied considerably among the stud farms, such as illustrated in the following two examples:

*DOI: http://dx.doi.org/10.5772/intechopen.92734*

when out at grass.

progress [16].

**5.3 Sustainable deworming**

relation to a standard ration of hay + concentrates.

animals' needs (at rest, light exercise, draft horse) (6/12).

illness affecting the immune system (e.g., Cushing's disease)).

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'… DOI: http://dx.doi.org/10.5772/intechopen.92734*

and quantity, thus enabling to further reduce the amount of concentrates, would not only control feed costs but also promote digestive health and the overall wellbeing of the horse [14, 15]. A simulation of the feed costs on a farm enabled to illustrate that a ration consisting of haylage + hay results in savings of up to 25% in relation to a standard ration of hay + concentrates.

Diets consisting of just hay, or hay + cereals, are often less balanced (~40 HDCP/ HFU ratio) compared with diets consisting of haylage (90 HDCP/HFU ratio, significantly more in line with the needs of the horse). Nevertheless, few stud farms (2/12) produce haylage. Eighty-three per cent of the stud farms monitored do not produce such forage, either because they have no knowledge of the harvest techniques (4/12) or because such forage constitutes too richer feed in relation to their animals' needs (at rest, light exercise, draft horse) (6/12).

Adding a vitamin-mineral supplement (VMS) to the ration is not systematic. Having said that, P, Cu, and Zn deficiencies were recorded on the forage analysed. A vitamin-mineral supplement is necessary not only in winter rations but also when out at grass.

#### **5.3 Sustainable deworming**

*Equine Science*

When the stocking rate in the spring exceeds 100 ares/LU (22/33 of the batches studied), practices aiming to intensify the farming system, such as the sale of forage or taking on boarding cattle, were proposed to breeders. Nevertheless, the lack of human resources, the necessary investment in harvesting equipment, and additional infrastructures (fencing and wintering barn), as well as the lack of economic production attractiveness (suckling cows), are the main blockers exposed by the stud farms for developing other activities to enable optimum use of the grassland. Since few references already exist on the interest of an equine-cattle grazing combination in grassy areas [6, 10], the French Horse and Equestrian Institute (IFCE) and the National Institute for Agricultural Research (INRA) are currently conducting studies in order to pinpoint its effects in relation to a farm's biotechnical,

Rotational grazing is considered as the most appropriate practice for providing an adequate energy and protein balance for animals requiring high nutritional needs (broodmares and foals), though without the necessity for concentrate supplementation and without body condition loss. The grass available must be of adequate quality (in leaf) and quantity (height between 5 and 20 cm) [12]. For those stud

For horses at rest, their living conditions take priority over the optimum use of grassland. Pasture management thus becomes somewhat tricky when trying to prevent overweight and consequential metabolic illnesses (laminitis) in adult horses having little or no exercise. Indeed, as a monogastric herbivore, diets with a low starch and sugar content are more adapted to horses, who have the ability to continuously ingest vast quantities of rough forage in order to satisfy their nutritional needs and maintain a healthy digestive system [13]. When grass resources are abundant, ingestion increases beyond the normal capacity in terms of the nutritional needs for maintaining a 3/5 body condition score, and the lack of exercise results in weight gain. Restricting food in winter, in order to encourage weight loss and to limit overweight just prior to the grazing season, could be a solution. Nevertheless, such practice is scarcely applied by breeders, the latter generally offering ad libitum

In spring, the grass available in leaf can represent a far too rich food resource (in energy and proteins) with over 50% of the grass analysis attaining + 132% of the HDCP needs and + 110% of the HFU needs for such horses already in good

Drylots are temporarily used for part of the day, or even 24/7, in order to restrict the food intake of overweight animals (horses and ponies) (body condition score corresponding to 4/5 at the end of winter). Low-protein fibrous forage is often administered in order to prevent metabolic illnesses (laminitis), notably when grass grows abundantly (spring, autumn). Such management raises the question of how to optimise the maintenance of such areas, not only in order to limit the propagation of weeds but also to maintain the weight-bearing ability of the ground in a manner not to damage the horses' hooves. An alternative, in order to prevent the degradation of drylots, sacrificed due to overgrazing, could be the creation of stabilised sandy areas where such horses could be parked during sensitive periods

None of the stud farms monitored undertook forage analysis, nor calculated routine rations, despite the diet administered to their horses consisting of forage, for the most part. An essentially forage-predominant diet in terms of proportion

economic, and social (labour) performances [11].

farms having thus invested, such practice should be long-lasting.

**196**

forage in winter.

(spring, autumn).

condition (BCS > 3.6) at the end of winter.

**5.2 Analysis of forage and winter rations**

The implementation of targeted deworming above the threshold of 200 epg in such equestrian structures enabled to simply worm half of the adult horses present on site during the grazing season. Such 200 epg threshold thus enables to preserve a parasite population not subject to anthelminthic treatment, the so-called refuge population [2]. The larger the refuge population, the less rapidly resistances progress [16].

Having said that, these dewormed horses were responsible for excreting more than 94% of eggs across the pastures. Targeted deworming thus enables to rupture the cycle of most parasites and hence to safeguard the health of all the horses on site.

One of the main hindrances to implementing targeted deworming within a structure seems, aside from the time spent in collecting individual stools, to be its cost. Indeed, Sallé et al. [17] illustrated that such targeted deworming can be financially viable in relation to systematic deworming insofar as the cost of a faecal egg count is less than 5 Euros. In the stud farms monitored, approximately ¼ of the horses had a low excretory status. Literature shows that such low excretory status is stable from one grazing season to the next [18, 19], for a healthy horse accommodated in stable conditions. In this study, 90% of the horses with this status in 2016 had the same status in 2017. For such horses, deworming once or twice a year (in autumn and possibly in spring) was recommended, without annual faecal egg count testing; only one faecal egg count approximately every 2–3 years in order to verify that the on-site epidemiological situation has not evolved and that the horse has not changed status. Annual faecal egg count monitoring is moreover recommended in the case of suspicion of immune deficiency (senior horse over the age of 20 or illness affecting the immune system (e.g., Cushing's disease)).

The cost of sustainable deworming could thus be reduced over the seasons due to the stability of the low excretory status requiring less strict faecal egg count.

Having said that, the high excretory status was much less stable in between the two grazing seasons, since only 37% of the horses with such status in 2016 also had the same status in 2017, and the remaining 63% passed from a high excretory status to an unstable status. For such unstable and high excretory statuses, it was advised to continue faecal egg count in order to adapt the frequency of deworming.

In terms of faecal egg count results, the situations varied considerably among the stud farms, such as illustrated in the following two examples:


It is thus difficult to implement an appropriate and acceptable targeted deworming protocol for all equine structures. This programme should be adapted to each stud farm, not only in accordance with the objectives of each farm (protection of the environment, health safety, economic considerations, and breeder implication) but also according to the epidemiological situation, such as the presence of foals and youngsters, or the frequency of movement, among others [2]. Nevertheless, good practices of stud management, enabling to reduce parasitic pressure across pastures, have been the subject of few studies in relation to horses, with the exception of dung removal [20] or composting manure [21]. We have attempted, during this project, to highlight the influence of certain types of stud management (presence or not of foals, accommodation, 24/7 grazing VS mixed rotational grazing, stocking rates, and importance of movements) on parasite excretion; nevertheless, no correlation was able to be established. Perhaps this was due to the limited number of horses selected for the study, or maybe due to the age of the horses (3 years and over), for which parasite immunity is deemed as being established [2]. Additional studies are thus necessary in order to research such risk factors within farms and to preach good practices of stud management [11].

#### **6. Conclusion**

Monitoring feed and pasture management in horses on 12 study farms for 2 years highlighted the necessity to alert horse breeders on the regular recording of the body condition score in order to optimise the balance between the needs of the animals, notably those with low nutritional needs, and the grass available in the pastures. Forage analysis and the calculation of a ration need to be more commonly accepted in order to ensure dietary balance and more targeted grazing. The parasitic monitoring in horses illustrated very heterogeneous situations among the structures. It seems very difficult to propose a sustainable deworming protocol without first carrying out a parasitic audit and ensuring strict monitoring of the farm by the treating veterinarian.

Several pasture management studies are currently ongoing in order to optimise feed and cost controls and to limit equine parasitic pressure, with notably a combined cattle-equine grazing study.

**199**

**Author details**

Pauline Doligez1

and Stéphanie Cassigneul8

3 ESA Angers (49), France

4 ENSAIA Nancy (54), France

Céline Saillet4

\*, Marie Delerue1

5 Chambre d'Agriculture de la Creuse (23), France

6 Chambre d'Agriculture de Corrèze (19), France

7 Chambre d'Agriculture de l'Indre (36), France

provided the original work is properly cited.

8 Chambre d'Agriculture du Calvados (14), France

\*Address all correspondence to: pauline.doligez@ifce.fr

, Hervé Feugère5

, Agnès Orsoni2

, Guillaume Mathieu6

1 Institut français du cheval et de l'équitation, La Jumenterie du Pin, Exmes, France

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 Institut français du cheval et de l'équitation, Arnac Pompadour, France

, Bathilde Diligeon3

, Jean Baptiste Quillet7

,

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'…*

*DOI: http://dx.doi.org/10.5772/intechopen.92734*

*Promoting Grass in Horse Diets and Implementing Sustainable Deworming: 'Équipâture'… DOI: http://dx.doi.org/10.5772/intechopen.92734*

#### **Author details**

*Equine Science*

rest of the herd.

• The first structure is a French Trotter breed farm with significant breeding and foaling activity, taking in many broodmares during the breeding season, these outside mares being lodged with the home-based horses. We noted a very high proportion of the horses with an unstable excretory status (80%) with only 20% of the horses with a stable status, of which only half, i.e., 10% overall, had a low excretory status. In such structure, targeted deworming has little interest, since most of the horses need to be dewormed following the faecal egg count. We notably observe high excretion levels in summer (1000 epg per horse in 2016, compared with 272 epg in spring 2016). Prior to introducing targeted deworming, certain stud-management measures should be implemented, in order to reduce contamination of the plots and infestation of the horses in summer, notably by separating the outside mares from the

• The second structure is an 'active stable', wherein the horses (essentially over the age of 15) benefit from mixed accommodation (a central stabilised area with rotational pastures during the grazing season, the dry areas being very regularly cleared of all dung). In this structure, ¾ of the horses had a stable status (54%

It is thus difficult to implement an appropriate and acceptable targeted deworming protocol for all equine structures. This programme should be adapted to each stud farm, not only in accordance with the objectives of each farm (protection of the environment, health safety, economic considerations, and breeder implication) but also according to the epidemiological situation, such as the presence of foals and youngsters, or the frequency of movement, among others [2]. Nevertheless, good practices of stud management, enabling to reduce parasitic pressure across pastures, have been the subject of few studies in relation to horses, with the exception of dung removal [20] or composting manure [21]. We have attempted, during this project, to highlight the influence of certain types of stud management (presence or not of foals, accommodation, 24/7 grazing VS mixed rotational grazing, stocking rates, and importance of movements) on parasite excretion; nevertheless, no correlation was able to be established. Perhaps this was due to the limited number of horses selected for the study, or maybe due to the age of the horses (3 years and over), for which parasite immunity is deemed as being established [2]. Additional studies are thus necessary in order to research such risk factors within farms and to

Monitoring feed and pasture management in horses on 12 study farms for 2 years highlighted the necessity to alert horse breeders on the regular recording of the body condition score in order to optimise the balance between the needs of the animals, notably those with low nutritional needs, and the grass available in the pastures. Forage analysis and the calculation of a ration need to be more commonly accepted in order to ensure dietary balance and more targeted grazing. The parasitic monitoring in horses illustrated very heterogeneous situations among the structures. It seems very difficult to propose a sustainable deworming protocol without first carrying out a parasitic audit and ensuring strict monitoring of the farm by the treating veterinarian. Several pasture management studies are currently ongoing in order to optimise feed and cost controls and to limit equine parasitic pressure, with notably a com-

with a low excretory status and 21% a high excretory status).

preach good practices of stud management [11].

bined cattle-equine grazing study.

**198**

**6. Conclusion**

Pauline Doligez1 \*, Marie Delerue1 , Agnès Orsoni2 , Bathilde Diligeon3 , Céline Saillet4 , Hervé Feugère5 , Guillaume Mathieu6 , Jean Baptiste Quillet<sup>7</sup> and Stéphanie Cassigneul8

1 Institut français du cheval et de l'équitation, La Jumenterie du Pin, Exmes, France

2 Institut français du cheval et de l'équitation, Arnac Pompadour, France

3 ESA Angers (49), France

4 ENSAIA Nancy (54), France

5 Chambre d'Agriculture de la Creuse (23), France

6 Chambre d'Agriculture de Corrèze (19), France

7 Chambre d'Agriculture de l'Indre (36), France

8 Chambre d'Agriculture du Calvados (14), France

\*Address all correspondence to: pauline.doligez@ifce.fr

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[4] INRA 2012- Nutrition et alimentation des chevaux (coord. W. Martin-Rosset). Editions Quae, Versailles, France

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[12] Collas C, Fleurance G, Cabaret J, Martin-Rosset W, Wimel L, Cortet J, et al. How does the suppression of energy supplementation affect herbage intake, performance and parasitism in lactating saddle mares? Animal. 2014;**8**(8):1290-1297

[13] Frape D. Equine Nutrition and Feeding. 4th ed. Oxford, UK: Wiley Blackwell; 2010

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[16] Van Wyk JA. Refugia overlooked as perhaps the most potent factor concerning the development of anthelminthic resistance. The Onderstepoort Journal of Veterinary Research. 2001;**68**:55-67

[17] Sallé G, Cortet J, Koch C, Reigner F, Cabaret J. Economic assessment of

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[18] Nielsen MK, Haaning N, Olsen SN. Strongyle egg shedding consistency in horses on farms using selective therapy in Denmark. Veterinary Parasitology.

[19] Becher A, Mahling M, Nielsen MK, Pfister K. Selective anthelmintic therapy of horses in the federal states of Bavaria (Germany) and Salzburg (Austria): An investigation into strongyle egg shedding consistency. Veterinary Parasitology. 2010;**171**:116-122

[20] Corbett CJ, Love S, Moore A, Burden FA, Matthews JB, Denwood MJ. The effectiveness of faecal removal methods of pasture management to control the cyathostomin burden of donkeys. Parasites & Vectors.

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2012;**191**:73-80

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FEC-based targeted selective drenching in horses. Veterinary Parasitology. 2015;**214**:159-166

[18] Nielsen MK, Haaning N, Olsen SN. Strongyle egg shedding consistency in horses on farms using selective therapy in Denmark. Veterinary Parasitology. 2006;**135**:333-335

[19] Becher A, Mahling M, Nielsen MK, Pfister K. Selective anthelmintic therapy of horses in the federal states of Bavaria (Germany) and Salzburg (Austria): An investigation into strongyle egg shedding consistency. Veterinary Parasitology. 2010;**171**:116-122

[20] Corbett CJ, Love S, Moore A, Burden FA, Matthews JB, Denwood MJ. The effectiveness of faecal removal methods of pasture management to control the cyathostomin burden of donkeys. Parasites & Vectors. 2014;**48**:1-7

[21] Gould JC, Rossano MG, Lawrence LM, Burk SV, Ennis RB, Lyons ET. The effects of windrow composting on the viability of *Parascaris equorum* eggs. Veterinary Parasitology. 2012;**191**:73-80

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*Equine Science*

**References**

[1] Nielsen MK, Mittel L, Grice A, Erskine M, Graves E, Vaala W, et al. AAEP Parasite Control Guidelines. 2017. Avaibale from: https://aaep. org/sites/default/files/Guidelines/ AAEPParasiteControlGuidelines.pdf en Basse Normandie. In: 26ème Journée de la Recherche Equine. Paris: Les Haras

[10] Bigot G, Célié A, Deminguet S, Perret E, Pavie J, Turpin N. Exploitation

des prairies dans des élevages de chevaux de sport en Basse-Normandie.

[11] Forteau L, Dumont B, Sallé G, Bigot G, Fleurance G. Horses grazing with cattle have reduced strongyle egg count due to the dilution effect and increased reliance on macrocyclic lactones in mixed farms. Animal. 2020;**14**(5):1076-1082. DOI: 10.1017/

[12] Collas C, Fleurance G, Cabaret J, Martin-Rosset W, Wimel L, Cortet J, et al. How does the suppression of energy supplementation affect herbage intake, performance and parasitism in lactating saddle mares? Animal.

[13] Frape D. Equine Nutrition and Feeding. 4th ed. Oxford, UK: Wiley

[14] Morhain B. Systèmes fourragers et d'alimentation du cheval dans différentes régions françaises. Revue

[15] Harris PA, Ellis AD, Fradinho MJ, Jansson A, Julliand V, Luthersson N, et al. Review: Feeding conserved forage to horses: Recent advances and recommendations. Animal.

[16] Van Wyk JA. Refugia overlooked as perhaps the most potent factor concerning the development of anthelminthic resistance. The Onderstepoort Journal of Veterinary

[17] Sallé G, Cortet J, Koch C, Reigner F, Cabaret J. Economic assessment of

Fourrages. 2011;**207**:155-163

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S1751731119002738

2014;**8**(8):1290-1297

Blackwell; 2010

2017;**11**(6):958-967

Research. 2001;**68**:55-67

Nationaux; 2000

[2] Cabaret J. Gestion durable des strongyloses chez le cheval à l'herbe: réduire le niveau d'infestation tout en limitant le risque de résistance aux anthelminthiques. Fourrages.

[3] INRA- IFCE- IE. Grille de notation de l'état corporel des chevaux de selle et de sport. Institut de l'Elevage, ed., Paris.

[4] INRA 2012- Nutrition et alimentation des chevaux (coord. W. Martin-Rosset).

Editions Quae, Versailles, France

[6] Trillaud-Geyl C, Leconte D, Cabaret J, Fleurance G, Martin RW. Conduite au pâturage (9th chapter). In: Nutrition et Alimentation des chevaux-Tables des apports alimentaires, INRA 2011. eds (Quae - Les Haras nationaux), 2011. pp. 185-205. ISBN: 978-2-7592- 1668-0. Journal of Animal and Feed

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[7] Poynter D. Seasonal fluctuations in the number of parasite eggs passed in horses. The Veterinary Record.

[8] Moulin C. Fonctionnement des systèmes d'alimentation à l'herbe pour différents types de chevaux proposition de méthodologie et premiers éléments d'analyse, Collection Lignes, éd (Institut

[9] Doligez E, Fouquet S. Enquête sur les pratiques de pâturage et l'entretien des prairies chez les éleveurs de chevaux

[5] Martin RW. Valeurs alimentaires des fourrages verts chez le cheval. Fourrages. 2011;**207**:173-180

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1997. p. 40

**203**

**Chapter 11**

**Abstract**

What Are They Thinking?

Mind of the Horse

and is relevant to safe horse handling.

**1. Introduction**

interacting with a horse.

gradient, horse home base, horse spatial gradient

latter include things like broken or unsecured tack.

*Ian Q. Whishaw and Candace J. Burke*

Scientific Horsemanship and the

Horse behavior in an arena is examined to determine their *Umwelt*, or point of view. When in an arena singly, horses displayed home base behavior, spending their time near the entrance, and excursion behavior, trips into the arena. At home bases, horses paced against the wall, pushed against the gate, looked out, and rolled. On excursions, they displayed a "sniff, look, and loop" pattern; sniffing the ground on the outward leg, looking with ears forward down the arena at the apex, making a faster return with ears back. When free with a pair mate, the area of its excursions expanded and if a pair mate was tethered at the far end of the arena, a horse shifted its home base to that location. When ridden, horses displayed similar sniff, look, and loop behavior centered toward the entrance. Experiments on memory for the arena showed it was good but was reset each day. A model suggests that behavior is shaped by a spatial gradient, in which stress expands in proportion to distance from home, and an exploratory gradient, in which patrolling is a part of each day's outing. Science-based horsemanship can provide insight into a horse's view of its world

**Keywords:** exploration of horse in arena, horse excursion, horse exploratory

The question, "what are they thinking?" in reference to horses has been addressed in many horse monographs and by many clinicians. Our intent is not to choose amongst suggested answers but to address the question by presenting a few of our own scientific studies. Science-based horsemanship can improve insight into horse behavior, contribute to the welfare of the horse, and improve safety for those

The statistics on injury related to handling or riding horses are consistent in every country in which they have been collected. The incidence of horse-related injury is due to the things that the horse does and to things that people do. The former includes things like "the horse spooked" or "the horse ran off" while the

Horse-related injuries outnumber injuries obtained in other sports, including contact sports such as rugby, football, and hockey [1–3]. Injuries occur almost as frequently when a person is at home, on a farm, or at an equestrian center.

#### **Chapter 11**

## What Are They Thinking? Scientific Horsemanship and the Mind of the Horse

*Ian Q. Whishaw and Candace J. Burke*

#### **Abstract**

Horse behavior in an arena is examined to determine their *Umwelt*, or point of view. When in an arena singly, horses displayed home base behavior, spending their time near the entrance, and excursion behavior, trips into the arena. At home bases, horses paced against the wall, pushed against the gate, looked out, and rolled. On excursions, they displayed a "sniff, look, and loop" pattern; sniffing the ground on the outward leg, looking with ears forward down the arena at the apex, making a faster return with ears back. When free with a pair mate, the area of its excursions expanded and if a pair mate was tethered at the far end of the arena, a horse shifted its home base to that location. When ridden, horses displayed similar sniff, look, and loop behavior centered toward the entrance. Experiments on memory for the arena showed it was good but was reset each day. A model suggests that behavior is shaped by a spatial gradient, in which stress expands in proportion to distance from home, and an exploratory gradient, in which patrolling is a part of each day's outing. Science-based horsemanship can provide insight into a horse's view of its world and is relevant to safe horse handling.

**Keywords:** exploration of horse in arena, horse excursion, horse exploratory gradient, horse home base, horse spatial gradient

#### **1. Introduction**

The question, "what are they thinking?" in reference to horses has been addressed in many horse monographs and by many clinicians. Our intent is not to choose amongst suggested answers but to address the question by presenting a few of our own scientific studies. Science-based horsemanship can improve insight into horse behavior, contribute to the welfare of the horse, and improve safety for those interacting with a horse.

The statistics on injury related to handling or riding horses are consistent in every country in which they have been collected. The incidence of horse-related injury is due to the things that the horse does and to things that people do. The former includes things like "the horse spooked" or "the horse ran off" while the latter include things like broken or unsecured tack.

Horse-related injuries outnumber injuries obtained in other sports, including contact sports such as rugby, football, and hockey [1–3]. Injuries occur almost as frequently when a person is at home, on a farm, or at an equestrian center.

Injury is equally likely when a person is on the ground handling a horse as it is when they are riding a horse. Injury is more likely if a person is a beginner than if experienced. The average age of an injury is about 30 years of age, but injuries can happen to people of all ages, with injuries more severe in females than in males. The highest risk of injury is to young females, perhaps because so many are engaged in equestrian sports.

Although a good deal has been written on the incidence and type of injury related to handling and riding horses, less attention has been given to prevention [2]. There are ways to reduce the chance of having an accident, and in the case of an accident, to reduce severity. Inexperienced riders can take lessons from a coach who teaches safety and riders can wear helmets. Owners or buyers can ensure that a horse is well trained. But even with such precautions the statistics on horse-related injuries do not seem to change, except that head injuries are less severe if a helmet is worn.

A science-based approach to handling and training horses can improve safety with horses. Starling et al. [4] outline a 10-point approach in which understanding horse ethology is the first point. Horse ethology is the study of the natural behavior of horses. For example, ethological studies show that feral horses are herd animals. They spend up to 16 h a day feeding. They are on the move much of the day. They are flight animals and run when frightened or threatened. But a central question is, how does horse ethology translate into a relationship with humans in typical equestrian interactions?

The purpose of the present chapter is to elaborate one aspect of horse ethology that has not received much attention, the horses' *Umwelt*, its point of view. Umwelt is the biological term used to describe the world view of an animal [5]. We certainly do not know the full dimension of the horse's world view [6, 7]. The following sections present some experiments that describe behavior in an equestrian arena that provide insight into a horse's umwelt in conditions in which it is being handled or ridden. These experiments will present ideas about how humans can shape their own umwelt to that of the horse and so develop habits to improve horse handling.

#### **2. Horse behavior in an arena**

We took 18 horses, varying in age and sex, individually into a riding arena, released them, and filmed them for 30 min [8]. This is a test that has been given to other animals in laboratory studies and it reveals how they adapt their behavior to an environment that is different from their home. We found that the horses spent most of that 30 min at the end of the area near the door through which they had entered the arena. **Figure 1** shows a sketch of the movement of one horse during the 30-min test. The horse did periodically go out into the arena, each of its excursions initially got a little longer than the first one, but soon the number of excursions decreased as did the size of the excursions until finally the horse remained near the door. This representative horse did not make it past the midpoint of the arena on any excursion.

We did this experiment with our 18 horses and we have also informally watched many other horses in similar situations. The behavior of the horses was similar whether they were geldings or mares, whether they had frequently been ridden in the arena, or had only occasionally been ridden in the arena. Their behavior was similar when the arena was completely new to them, having been hauled to the arena from another farm. The behavior was similar for horses stabled inside, stabled right beside the arena, or at some distance away. Some of the horses were Thoroughbreds, some were American Quarter Horses, and some were mixed

**205**

child's home base.

them away from the gate.

**Figure 1.**

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse*

breeds. They all behaved in much the same way. On many occasions we have observed handlers turn their horse out in the arena to exercise only to find them loitering by the gate. To encourage them to exercise, the handler might then chase

*on the home base consisted of stops, pacing, pushing against the gate, and rolling.*

The location at which an animal hangs out when placed in a novel environment is called a home base. Many different species of animal have been found to choses one or more locations—home bases—in the test area in which they spend most of their time. The behavior was first described in laboratory rats [9, 10]. Rats placed in a new environment initially remain in an area close to the entrance point and make excursions from there only to return again. If they find a more secure location, as defined by a corner or a part of the arena where a dark object is located, they move their home base to that location. Rats like areas beside walls and they like dark places. The home base for the horse in our study was the entrance point. The horses appear to otherwise avoid walls and avoid dark locations. People display home base behavior as well. Scientists have observed the behavior of small children who were taken to a novel room with their mother [11]. The children made excursions away from the mother but always returned to her. The mother's location defines the

*The organization of the exploratory behavior of a single horse released into an arena for 30 min. (A) The horse spent most of its time near the entrance gate, its home base. Periodic excursions consist of an outward leg (blue) and a homeward leg (red) but none of the excursions went past the center of the arena. (B) Activities centered* 

Behavior in a home base is characteristic. This is where a horse paces back and forth against the wall, looks out over the gate in a direction away from the arena, leans against the gate, and rolls (see **Figure 1**). Home base behavior for the horse is organized and it is different from behavior that takes a horse away from a home base.

*DOI: http://dx.doi.org/10.5772/intechopen.91209*

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse DOI: http://dx.doi.org/10.5772/intechopen.91209*

#### **Figure 1.**

*Equine Science*

is worn.

engaged in equestrian sports.

equestrian interactions?

**2. Horse behavior in an arena**

Injury is equally likely when a person is on the ground handling a horse as it is when they are riding a horse. Injury is more likely if a person is a beginner than if experienced. The average age of an injury is about 30 years of age, but injuries can happen to people of all ages, with injuries more severe in females than in males. The highest risk of injury is to young females, perhaps because so many are

Although a good deal has been written on the incidence and type of injury related to handling and riding horses, less attention has been given to prevention [2]. There are ways to reduce the chance of having an accident, and in the case of an accident, to reduce severity. Inexperienced riders can take lessons from a coach who teaches safety and riders can wear helmets. Owners or buyers can ensure that a horse is well trained. But even with such precautions the statistics on horse-related injuries do not seem to change, except that head injuries are less severe if a helmet

A science-based approach to handling and training horses can improve safety with horses. Starling et al. [4] outline a 10-point approach in which understanding horse ethology is the first point. Horse ethology is the study of the natural behavior of horses. For example, ethological studies show that feral horses are herd animals. They spend up to 16 h a day feeding. They are on the move much of the day. They are flight animals and run when frightened or threatened. But a central question is, how does horse ethology translate into a relationship with humans in typical

The purpose of the present chapter is to elaborate one aspect of horse ethology that has not received much attention, the horses' *Umwelt*, its point of view. Umwelt is the biological term used to describe the world view of an animal [5]. We certainly do not know the full dimension of the horse's world view [6, 7]. The following sections present some experiments that describe behavior in an equestrian arena that provide insight into a horse's umwelt in conditions in which it is being handled or ridden. These experiments will present ideas about how humans can shape their own umwelt to that of the horse and so develop habits to improve horse handling.

We took 18 horses, varying in age and sex, individually into a riding arena, released them, and filmed them for 30 min [8]. This is a test that has been given to other animals in laboratory studies and it reveals how they adapt their behavior to an environment that is different from their home. We found that the horses spent most of that 30 min at the end of the area near the door through which they had entered the arena. **Figure 1** shows a sketch of the movement of one horse during the 30-min test. The horse did periodically go out into the arena, each of its excursions initially got a little longer than the first one, but soon the number of excursions decreased as did the size of the excursions until finally the horse remained near the door. This representative horse did not make it past the midpoint of the arena on

We did this experiment with our 18 horses and we have also informally watched

many other horses in similar situations. The behavior of the horses was similar whether they were geldings or mares, whether they had frequently been ridden in the arena, or had only occasionally been ridden in the arena. Their behavior was similar when the arena was completely new to them, having been hauled to the arena from another farm. The behavior was similar for horses stabled inside, stabled right beside the arena, or at some distance away. Some of the horses were Thoroughbreds, some were American Quarter Horses, and some were mixed

**204**

any excursion.

*The organization of the exploratory behavior of a single horse released into an arena for 30 min. (A) The horse spent most of its time near the entrance gate, its home base. Periodic excursions consist of an outward leg (blue) and a homeward leg (red) but none of the excursions went past the center of the arena. (B) Activities centered on the home base consisted of stops, pacing, pushing against the gate, and rolling.*

breeds. They all behaved in much the same way. On many occasions we have observed handlers turn their horse out in the arena to exercise only to find them loitering by the gate. To encourage them to exercise, the handler might then chase them away from the gate.

The location at which an animal hangs out when placed in a novel environment is called a home base. Many different species of animal have been found to choses one or more locations—home bases—in the test area in which they spend most of their time. The behavior was first described in laboratory rats [9, 10]. Rats placed in a new environment initially remain in an area close to the entrance point and make excursions from there only to return again. If they find a more secure location, as defined by a corner or a part of the arena where a dark object is located, they move their home base to that location. Rats like areas beside walls and they like dark places. The home base for the horse in our study was the entrance point. The horses appear to otherwise avoid walls and avoid dark locations. People display home base behavior as well. Scientists have observed the behavior of small children who were taken to a novel room with their mother [11]. The children made excursions away from the mother but always returned to her. The mother's location defines the child's home base.

Behavior in a home base is characteristic. This is where a horse paces back and forth against the wall, looks out over the gate in a direction away from the arena, leans against the gate, and rolls (see **Figure 1**). Home base behavior for the horse is organized and it is different from behavior that takes a horse away from a home base.

#### **3. Sniff, look, and loop**

When horses leave a home base, their away behavior is also organized. Each trip forms a loop, in which a horse ventures away from the starting point and then returns to it. The outward trip is generally slow and sometimes features stops. The homeward trip is faster with stops less likely. If the loop takes a horse well into the arena, it may trot or even gallop back. On an outward trip a horse will often lower its head and sniff the ground. When reaching the apex of an excursion, it may stop and look toward the far end of the arena with head erect and ears pointing forward. It may then put one ear back, indicating the direction in which it will turn, drop its head, and with ears in a relatively neutral position or back, make the homeward trip. To highlight major features of this organization we call the behavior "sniff, look, and loop" and it is illustrated in **Figure 2**. Note that the horse in **Figure 2** has its tail up at the sniff and look points, suggesting waryness.

Sniff, look, and loop describe the organized ways that a horse investigates the area surrounding the home base. Sniffing the arena likely helps it to determine what other horses may have been there. A horse has one of the largest eyes of all animals and excellent vision and so it need not go to the far end of the arena to visually investigate it [12]. Its ears forward posture allows it to investigate sounds both inside and outside the arena. Its homeward trip is quicker because its investigatory

#### **Figure 2.**

*Stop, look, and loop. Activities that occurred on a single excursion. (A) Sniff, the horse's head is lowered as it sniffs the ground on the outward leg of an excursion. (B) Look, a horse looks and sometimes stops and looks, with head erect and ears forward toward the far end of the arena. (C) Loop, the horse turns, often signaling the direction of turn with the retraction of the ipsilateral ear, and returns to its starting point, usually with ears back and head somewhat lowered. (D) Home base, the horse stands and looks outward. Note: tail up postures at sniff and look.*

**207**

**Figure 3.**

*paths).*

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse*

excursion is over and it can hurry back to the home base. According to the principles of optimal foraging theory, when business is done on an outward trip, it is safest not to tarry on the homeward trip [13]. Having its ears neutral or back on the homeward trip seems to suggest that a horse may be attending to what might be behind it, perhaps the unexplored arena, with which it is not comfortable. It may

One explanation of home base behavior is that a horse stays near the gate because that is where it entered the arena. That location might be perceived as the shortest way back to its home paddock and its herd, which is its actual home. In short, it wants to "be at home with its buddies," as every horse person can attest. We examined this idea by giving four horses the same 30 min test as described above and observed that these horses set up their home base near the gate. We then brought a pair mate into the arena and tied it at the far end of the arena for another 30 min test. The horse that was free to move immediately moved to the far end of the arena, the area of the arena that it previously avoided, and spent the half hour

This experiment suggests that what motivates the horse to remain near the gate end of the arena is that this is a place that is closest to its herd. For horses that were stalled individually in the arena, the herd explanation may still apply because they

The home paddock may also be attractive to a horse, however, because that is where it ordinarily finds safety and where it is fed. We tested this idea by turning out pair mates at liberty in the arena. When free the horses still displayed home base behavior and spent most of their time near the door where they also rolled. Rather than pacing, however, they spent time investigating objects near the door. Their loop excursions were much larger and frequently much faster. **Figure 4** illustrates the movements of one horse when it was in the arena alone and the movements of the same horse when it was in the arena with a pair mate. These experiments show that one reason a horse may form a home base near the door is that it wants to return to its pair mate but another reason is that it wants to return to its home

*Movement in two 30-min tests. When a horse was alone, it spent its time near the gate (red paths). When a familiar horse was tethered at the far end of the arena, the free horse moved to the far end of the arena (blue* 

*DOI: http://dx.doi.org/10.5772/intechopen.91209*

also be relaxing as it returns to its home base.

near the pair mate (**Figure 3**).

**4. The home base as a surrogate for the herd**

can see neighboring horses and so treat them as the herd.

territory. In its natural ecology, the two coincide.

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse DOI: http://dx.doi.org/10.5772/intechopen.91209*

excursion is over and it can hurry back to the home base. According to the principles of optimal foraging theory, when business is done on an outward trip, it is safest not to tarry on the homeward trip [13]. Having its ears neutral or back on the homeward trip seems to suggest that a horse may be attending to what might be behind it, perhaps the unexplored arena, with which it is not comfortable. It may also be relaxing as it returns to its home base.

#### **4. The home base as a surrogate for the herd**

*Equine Science*

**3. Sniff, look, and loop**

When horses leave a home base, their away behavior is also organized. Each trip forms a loop, in which a horse ventures away from the starting point and then returns to it. The outward trip is generally slow and sometimes features stops. The homeward trip is faster with stops less likely. If the loop takes a horse well into the arena, it may trot or even gallop back. On an outward trip a horse will often lower its head and sniff the ground. When reaching the apex of an excursion, it may stop and look toward the far end of the arena with head erect and ears pointing forward. It may then put one ear back, indicating the direction in which it will turn, drop its head, and with ears in a relatively neutral position or back, make the homeward trip. To highlight major features of this organization we call the behavior "sniff, look, and loop" and it is illustrated in **Figure 2**. Note that the horse in **Figure 2** has

Sniff, look, and loop describe the organized ways that a horse investigates the area surrounding the home base. Sniffing the arena likely helps it to determine what other horses may have been there. A horse has one of the largest eyes of all animals and excellent vision and so it need not go to the far end of the arena to visually investigate it [12]. Its ears forward posture allows it to investigate sounds both inside and outside the arena. Its homeward trip is quicker because its investigatory

*Stop, look, and loop. Activities that occurred on a single excursion. (A) Sniff, the horse's head is lowered as it sniffs the ground on the outward leg of an excursion. (B) Look, a horse looks and sometimes stops and looks, with head erect and ears forward toward the far end of the arena. (C) Loop, the horse turns, often signaling the direction of turn with the retraction of the ipsilateral ear, and returns to its starting point, usually with ears back and head somewhat lowered. (D) Home base, the horse stands and* 

its tail up at the sniff and look points, suggesting waryness.

**206**

**Figure 2.**

*looks outward. Note: tail up postures at sniff and look.*

One explanation of home base behavior is that a horse stays near the gate because that is where it entered the arena. That location might be perceived as the shortest way back to its home paddock and its herd, which is its actual home. In short, it wants to "be at home with its buddies," as every horse person can attest. We examined this idea by giving four horses the same 30 min test as described above and observed that these horses set up their home base near the gate. We then brought a pair mate into the arena and tied it at the far end of the arena for another 30 min test. The horse that was free to move immediately moved to the far end of the arena, the area of the arena that it previously avoided, and spent the half hour near the pair mate (**Figure 3**).

This experiment suggests that what motivates the horse to remain near the gate end of the arena is that this is a place that is closest to its herd. For horses that were stalled individually in the arena, the herd explanation may still apply because they can see neighboring horses and so treat them as the herd.

The home paddock may also be attractive to a horse, however, because that is where it ordinarily finds safety and where it is fed. We tested this idea by turning out pair mates at liberty in the arena. When free the horses still displayed home base behavior and spent most of their time near the door where they also rolled. Rather than pacing, however, they spent time investigating objects near the door. Their loop excursions were much larger and frequently much faster. **Figure 4** illustrates the movements of one horse when it was in the arena alone and the movements of the same horse when it was in the arena with a pair mate. These experiments show that one reason a horse may form a home base near the door is that it wants to return to its pair mate but another reason is that it wants to return to its home territory. In its natural ecology, the two coincide.

#### **Figure 3.**

*Movement in two 30-min tests. When a horse was alone, it spent its time near the gate (red paths). When a familiar horse was tethered at the far end of the arena, the free horse moved to the far end of the arena (blue paths).*

#### **Figure 4.**

*The movements of a horse when in the arena alone (red paths) and when with a pair mate (blue paths). The area of movement of the horse expanded with the pair mate present but movement was centered on the "home base" door area.*

#### **5. Behavior under saddle**

We asked what a horse's spontaneous behavior would be like if it were ridden but otherwise left alone. We used reining horses for the experiment because they are well schooled. All were familiar with the arena because it was their home arena and they had been frequently ridden there. We asked whether a horse would display elements of sniff, look, and loop behavior when ridden? We had riders do our 30-min test. We asked them to encourage the horse to leave the area entrance but once the horse began to do so, put down the reins and let the horse proceed as it wished. If the horse returned to the entrance, then after a pause, again ask the horse to leave. All of the horses made an excursion into the area when asked to do so and then they spontaneously stopped and looked down the arena, turned and returned to the starting point more quickly. For one of the horses the outward leg of the excursion was quite long and this was the only horse that went past the midpoint of the area. For all of the horses, successive excursions initially got a little longer and then progressively got shorter (**Figure 5**). The horses also came back more directly and more quickly than they went out. One horse first trotted back but on successive trips its speed increased until on one excursion, it galloped back. Two of the horses also sniffed the ground on the way out and all were more likely to have their ears up on the outward leg of a loop and their ears back on the homeward leg of a loop. These results suggest that the exploratory behavior of a horse under saddle reflects its behavior when it is at liberty.

We investigated whether stop, look, and loop behavior would influence a more typical riding session. We had riders enter the area singly and trot their horse around the edge of the arena, with the horse on a loose rein, so that the horse was free to choose its speed. At the same time, we timed the away and back legs of each of 10 trips. All of the horses spontaneously slowed their trotting speed as they left the gate end of the arena and they spontaneously increased their trotting speed as they left the far end of the arena on their trip back toward the gate. Consequently, the times taken to return were statistically shorter than the times to venture out. In addition, as a horse left the near end of the arena, it most often had its ears forward and looked toward the far end of the arena to which it was going. On the homeward leg of the trip, it noticeably lowered its head and frequently had its ears back (**Figure 6**). Thus, even though the horses were willingly circling the area under the guidance of a rider, they were noticeably engaging in behavior that they displayed when making

**209**

**Figure 6.**

*homeward leg.*

**Figure 5.**

two ends of the arena.

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse*

sniff, look, and loop trips when on their own—their going out was slow and their coming back faster and their ear position reflected their relative concern with the

*Ear position on outward and inward directions when circling an arena under saddle. (A) On the outward leg of the circle the horse frequently directs its ears forward. (B) On the homeward leg of a circle the horse frequently directs its ears backward. Ear position may signal caution on the outward leg and relaxation on the* 

*Loops made by a horse under saddle. The horse was asked to walk into the arena and then released from control. Note: the horse made repeated loops near the gate area of the arena. The colored bar indicates time.*

The observation that ear position is a marker of the inward and outward loops of spontaneous excursions and excursions under saddle suggests that ear position could be a marker of behavior in the show pen. We used videos from the nonpro National Reining Horse Association reigning futurity held in Oklahoma

*DOI: http://dx.doi.org/10.5772/intechopen.91209*

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse DOI: http://dx.doi.org/10.5772/intechopen.91209*

#### **Figure 5.**

*Equine Science*

**Figure 4.**

*base" door area.*

**5. Behavior under saddle**

its behavior when it is at liberty.

We asked what a horse's spontaneous behavior would be like if it were ridden but otherwise left alone. We used reining horses for the experiment because they are well schooled. All were familiar with the arena because it was their home arena and they had been frequently ridden there. We asked whether a horse would display elements of sniff, look, and loop behavior when ridden? We had riders do our 30-min test. We asked them to encourage the horse to leave the area entrance but once the horse began to do so, put down the reins and let the horse proceed as it wished. If the horse returned to the entrance, then after a pause, again ask the horse to leave. All of the horses made an excursion into the area when asked to do so and then they spontaneously stopped and looked down the arena, turned and returned to the starting point more quickly. For one of the horses the outward leg of the excursion was quite long and this was the only horse that went past the midpoint of the area. For all of the horses, successive excursions initially got a little longer and then progressively got shorter (**Figure 5**). The horses also came back more directly and more quickly than they went out. One horse first trotted back but on successive trips its speed increased until on one excursion, it galloped back. Two of the horses also sniffed the ground on the way out and all were more likely to have their ears up on the outward leg of a loop and their ears back on the homeward leg of a loop. These results suggest that the exploratory behavior of a horse under saddle reflects

*The movements of a horse when in the arena alone (red paths) and when with a pair mate (blue paths). The area of movement of the horse expanded with the pair mate present but movement was centered on the "home* 

We investigated whether stop, look, and loop behavior would influence a more typical riding session. We had riders enter the area singly and trot their horse around the edge of the arena, with the horse on a loose rein, so that the horse was free to choose its speed. At the same time, we timed the away and back legs of each of 10 trips. All of the horses spontaneously slowed their trotting speed as they left the gate end of the arena and they spontaneously increased their trotting speed as they left the far end of the arena on their trip back toward the gate. Consequently, the times taken to return were statistically shorter than the times to venture out. In addition, as a horse left the near end of the arena, it most often had its ears forward and looked toward the far end of the arena to which it was going. On the homeward leg of the trip, it noticeably lowered its head and frequently had its ears back (**Figure 6**). Thus, even though the horses were willingly circling the area under the guidance of a rider, they were noticeably engaging in behavior that they displayed when making

**208**

*Loops made by a horse under saddle. The horse was asked to walk into the arena and then released from control. Note: the horse made repeated loops near the gate area of the arena. The colored bar indicates time.*

#### **Figure 6.**

*Ear position on outward and inward directions when circling an arena under saddle. (A) On the outward leg of the circle the horse frequently directs its ears forward. (B) On the homeward leg of a circle the horse frequently directs its ears backward. Ear position may signal caution on the outward leg and relaxation on the homeward leg.*

sniff, look, and loop trips when on their own—their going out was slow and their coming back faster and their ear position reflected their relative concern with the two ends of the arena.

The observation that ear position is a marker of the inward and outward loops of spontaneous excursions and excursions under saddle suggests that ear position could be a marker of behavior in the show pen. We used videos from the nonpro National Reining Horse Association reigning futurity held in Oklahoma

#### **Figure 7.**

*Number of horses displaying either mainly ears forward or neutral position when walking into an arena or walking out of the arena as a part of reining Pattern 6. Results obtained from the non-pro National Reining Horse Association futurity in Oklahoma City in 2015.*

City in 2015. The horses were performing Pattern 6, a pattern in which they walk to the center of the arena to begin the pattern and walk much the same path to the entrance gate after making their last stop. We rated ear position on the inward and outward walks. As is illustrated in **Figure 7**, inward walks were overwhelmingly associated with periods of ears forward position whereas outward walks were associated with a relatively neutral or ear back position. It is noteworthy that many riders try to minimize "look" behavior on the outward walk by collecting their horse. These results suggest that just as horses treat the outward portion of a spontaneous loop as stressful, even when well-trained they display the same behavior when performing in an arena.

#### **6. Memory**

The similarity of home-base behavior of horses that were familiar with the arena and those who were taken to the arena for the first time might suggest that horses have a poor memory of the arena. Horses that are familiar with the arena seemed to behave as if they are being introduced to it for the first time, as judged by a comparison of their behavior to the behavior of horses that were new to the arena. Many studies have noted that horses have good memory [14–19], but our question related to the memory for an arena they had previously visited. We tested arena memory with five horses that had been ridden in the arena a number of times each week for many weeks. The arena baseboard was painted white but was covered with dust and scuff marks from being hit by the tires of the tractor that was used to groom the arena. We placed a novel object on the arena wall, a three-inch wide two-foot long strip of cloth. If the horses were treating the arena as a completely new place, they should not notice the cue because it would look to them like other marks on the wall. If they had a memory for the arena, they might notice the cue. The riders were unaware of our experiment. We took any especially attentive or avoidance behavior of the horses toward the cue as a sign that they recognized that the cue was there.

All of the horses immediately noticed the cue when the riders first circled the arena past the cue, and two of the horses shied noticeably, surprising the riders who did not seem to have noticed the cue themselves. The results of this experiment suggest to us that the horse have an excellent memory for the arena—excellent in the sense that they recognize something new against a background that is familiar to them.

**211**

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse*

were walking and approaching objects that they saw there.

were all associated with visits to droppings.

they had sniffed a half hour previously.

Accordingly, their home-base behavior and seeming avoidance of the far end of the arena on the exploratory tests cannot be explained in relation to poor memory for the arena. They were not avoiding the far end of the area because they had no memory of

In the course of studying why horses might sniff the ground during a warm-up

In the course of studying this sniffing behavior we observed that a horse very seldom returned to an object once it had sniffed it. That they did not return to objects indicated that they remembered them. To further examine this form of object memory, we purposefully manipulated the delay between the first approach to sniff of an object and subsequent responses to the same object. We had a rider allow a horse to approach and sniff an object and then return along the same path to see whether the horse would again approach the object. We varied the return time by minutes, as measured by a complete circle around the arena at a walk, to a half an hour, as timed with a watch. We found that the interval did not matter, of 297 instances of return visit opportunities, only 9 were associated with a second visit to an object (results collected from four horses). We also did tests of having the horses approach the object from a different direction. Again, of 75 instances of returns, only four were associated with the second inspection of an object. The second visits

Accordingly, we made droppings a focus of examination. We allowed a horse to walk directly toward a dropping and sniff it and we timed the duration of the sniff. We then varied the time of our next visit on which we allowed the horse to walk directly toward the dropping. Of 150 such samples, on 137 occasions the horses did not sniff the dropping on the second trip but passed by. On the few occasions on which they sniffed on a return visit, the duration of sniffing was shorter than on the previous visit. There was no effect of the intertrial interval, as horses mainly ignored a target that they had recently sniffed as much as they ignored a target that

We placed two plates containing droppings approximately 30 ft. away from each other and had a rider walk a horse toward the center of the space between the objects (**Figure 8**). Even at quite a long distance away, the horses veered toward one of the objects to sniff it. Then within a few minutes to as long as 30 min later, the test was repeated. Each horse then got a third trial, with the expectation that once they had examined both objects, they might ignore them on the third trial. The horses were given one test each day—with test at the short interval and the test at the 30-min interval alternated each day. For the tests, the objects were at different locations in the area each day. Thus, over 20 days the horse had 10 tests at the short interval and 10 tests at the long interval. The results are shown in **Figure 9**. One horse got 10/10 (they alternated on each of 10 trials) at both the short and the long interval and the other horse got 9/10 at the short interval and 9/10 at the long interval. On their third trial, both horses ignored both objects on 10/10 trials, so indicating that they remember that they had explored them. This experiment indicated that horses have an excellent short-term memory of objects that they get to sniff.

for riding, we observed that the horses would notice objects on the ground, go toward them and sniff them. The objects could be as small as a cigarette butt or a blade of hay, a sunbeam from a window, or the droppings left by a previous horse. We collected observations of sniffing and checking behavior as a way of assessing visual attention and memory. We found that horses would notice a small object as far as 10 feet away and a large object, such as the dropping from another horse, from as far as 30 feet away. When given the opportunity, the horses were very attentive to the ground and their inspection of the arena did not just consist of looking at objects in the distance but also consisted of inspecting the ground on which they

*DOI: http://dx.doi.org/10.5772/intechopen.91209*

ever being there.

*Equine Science*

**Figure 7.**

City in 2015. The horses were performing Pattern 6, a pattern in which they walk to the center of the arena to begin the pattern and walk much the same path to the entrance gate after making their last stop. We rated ear position on the inward and outward walks. As is illustrated in **Figure 7**, inward walks were overwhelmingly associated with periods of ears forward position whereas outward walks were associated with a relatively neutral or ear back position. It is noteworthy that many riders try to minimize "look" behavior on the outward walk by collecting their horse. These results suggest that just as horses treat the outward portion of a spontaneous loop as stressful, even when well-trained they

*Number of horses displaying either mainly ears forward or neutral position when walking into an arena or walking out of the arena as a part of reining Pattern 6. Results obtained from the non-pro National Reining* 

The similarity of home-base behavior of horses that were familiar with the arena and those who were taken to the arena for the first time might suggest that horses have a poor memory of the arena. Horses that are familiar with the arena seemed to behave as if they are being introduced to it for the first time, as judged by a comparison of their behavior to the behavior of horses that were new to the arena. Many studies have noted that horses have good memory [14–19], but our question related to the memory for an arena they had previously visited. We tested arena memory with five horses that had been ridden in the arena a number of times each week for many weeks. The arena baseboard was painted white but was covered with dust and scuff marks from being hit by the tires of the tractor that was used to groom the arena. We placed a novel object on the arena wall, a three-inch wide two-foot long strip of cloth. If the horses were treating the arena as a completely new place, they should not notice the cue because it would look to them like other marks on the wall. If they had a memory for the arena, they might notice the cue. The riders were unaware of our experiment. We took any especially attentive or avoidance behavior of the horses toward the cue as a sign that they recognized that the cue was there. All of the horses immediately noticed the cue when the riders first circled the arena

past the cue, and two of the horses shied noticeably, surprising the riders who did not seem to have noticed the cue themselves. The results of this experiment suggest to us that the horse have an excellent memory for the arena—excellent in the sense that they recognize something new against a background that is familiar to them.

display the same behavior when performing in an arena.

*Horse Association futurity in Oklahoma City in 2015.*

**210**

**6. Memory**

Accordingly, their home-base behavior and seeming avoidance of the far end of the arena on the exploratory tests cannot be explained in relation to poor memory for the arena. They were not avoiding the far end of the area because they had no memory of ever being there.

In the course of studying why horses might sniff the ground during a warm-up for riding, we observed that the horses would notice objects on the ground, go toward them and sniff them. The objects could be as small as a cigarette butt or a blade of hay, a sunbeam from a window, or the droppings left by a previous horse. We collected observations of sniffing and checking behavior as a way of assessing visual attention and memory. We found that horses would notice a small object as far as 10 feet away and a large object, such as the dropping from another horse, from as far as 30 feet away. When given the opportunity, the horses were very attentive to the ground and their inspection of the arena did not just consist of looking at objects in the distance but also consisted of inspecting the ground on which they were walking and approaching objects that they saw there.

In the course of studying this sniffing behavior we observed that a horse very seldom returned to an object once it had sniffed it. That they did not return to objects indicated that they remembered them. To further examine this form of object memory, we purposefully manipulated the delay between the first approach to sniff of an object and subsequent responses to the same object. We had a rider allow a horse to approach and sniff an object and then return along the same path to see whether the horse would again approach the object. We varied the return time by minutes, as measured by a complete circle around the arena at a walk, to a half an hour, as timed with a watch. We found that the interval did not matter, of 297 instances of return visit opportunities, only 9 were associated with a second visit to an object (results collected from four horses). We also did tests of having the horses approach the object from a different direction. Again, of 75 instances of returns, only four were associated with the second inspection of an object. The second visits were all associated with visits to droppings.

Accordingly, we made droppings a focus of examination. We allowed a horse to walk directly toward a dropping and sniff it and we timed the duration of the sniff. We then varied the time of our next visit on which we allowed the horse to walk directly toward the dropping. Of 150 such samples, on 137 occasions the horses did not sniff the dropping on the second trip but passed by. On the few occasions on which they sniffed on a return visit, the duration of sniffing was shorter than on the previous visit. There was no effect of the intertrial interval, as horses mainly ignored a target that they had recently sniffed as much as they ignored a target that they had sniffed a half hour previously.

We placed two plates containing droppings approximately 30 ft. away from each other and had a rider walk a horse toward the center of the space between the objects (**Figure 8**). Even at quite a long distance away, the horses veered toward one of the objects to sniff it. Then within a few minutes to as long as 30 min later, the test was repeated. Each horse then got a third trial, with the expectation that once they had examined both objects, they might ignore them on the third trial. The horses were given one test each day—with test at the short interval and the test at the 30-min interval alternated each day. For the tests, the objects were at different locations in the area each day. Thus, over 20 days the horse had 10 tests at the short interval and 10 tests at the long interval. The results are shown in **Figure 9**. One horse got 10/10 (they alternated on each of 10 trials) at both the short and the long interval and the other horse got 9/10 at the short interval and 9/10 at the long interval. On their third trial, both horses ignored both objects on 10/10 trials, so indicating that they remember that they had explored them. This experiment indicated that horses have an excellent short-term memory of objects that they get to sniff.

#### **Figure 8.**

*Two choice memory test. (A) A horse ridden to the center point between two plates containing droppings, approaches the right plate and sniffs the target. (B) About 5 min later, the horse is given a second choice and chooses the left target. (C) About 5 min later, the horse is given a third choice and passes both targets without investigating either.*

Our memory experiment shows that the horses always treated objects as novel on each day's encounter. We also tested horses in an outdoor arena, where droppings and other objects tended to be left because the arena received infrequent grooming. There, we found that the horses explored as many as six objects and remember them

**213**

**8. Discussion**

of an arena to which they are taken.

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse*

on a same day test. There too, when they were returned on the following day, they behaved toward the object as if they had never previously seen them. This experiment suggests that when removed from the arena for a day, a horse resets its memory

*Two choice test results (percent choices). On the second choice given either 5 or 30 min after the first choice there is a high probability that the horses choose the target not chosen on the first trial. On the third choice, there is a high probability that the horses choose neither target. Both results show that a horse remembers targets that it* 

The experiments on memory show that horses are motivated to investigate/ check small objects on the ground and they then remember those objects during the period of time that they are in the arena. It is well known that horses shy at novel objects and we reasoned that if we increased the size of the objects, their behavior should transition from investigatory to avoidance behavior. We made round cut outs of cardboard of various sizes and measured approach and avoidance behavior as we rode the horses around the arena. We found that as the size of the object increased, the probability of avoidance behavior increased. This behavior is very similar to that described by Ewart [20] for toads, which approach to eat small objects that he presented to them and who avoided larger objects that he presented, treating them as predators. We also varied the location of the objects in the arena and found that objects were avoided with more vigor at the far end of the arena. Often, an intermediate size object that was avoided at the far end of the arena was investigated at the near end of the arena. Interestingly, the horses were still likely to shy at large objects when returned to the object a short time later. Since their memory for objects in an

arena is good, repeated shying appeared unlikely due to poor memory.

These experiments tell us two main things about what a horse is thinking when it is taken into an arena. First, the arena is a source of stress and it is likely that it is anxiety provoking. Second, a horse views the arena as a place that is novel and that requires inspection and when not novel a place that must be patrolled and checked. In responding to these two influences, horses display a *spatial gradient* and an *exploratory gradient*. These gradients, if attended to, allow a rider to read the mind of their horse and adjust their ride and their training. We will point out some of the ways that more expert horse handlers show that they are aware of a horse's opinion

*DOI: http://dx.doi.org/10.5772/intechopen.91209*

and treats the objects in the arena as new.

**7. Checking and shying**

**Figure 9.**

*has investigated.*

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse DOI: http://dx.doi.org/10.5772/intechopen.91209*

**Figure 9.**

*Equine Science*

**212**

**Figure 8.**

*investigating either.*

Our memory experiment shows that the horses always treated objects as novel on each day's encounter. We also tested horses in an outdoor arena, where droppings and other objects tended to be left because the arena received infrequent grooming. There, we found that the horses explored as many as six objects and remember them

*Two choice memory test. (A) A horse ridden to the center point between two plates containing droppings, approaches the right plate and sniffs the target. (B) About 5 min later, the horse is given a second choice and chooses the left target. (C) About 5 min later, the horse is given a third choice and passes both targets without*  *Two choice test results (percent choices). On the second choice given either 5 or 30 min after the first choice there is a high probability that the horses choose the target not chosen on the first trial. On the third choice, there is a high probability that the horses choose neither target. Both results show that a horse remembers targets that it has investigated.*

on a same day test. There too, when they were returned on the following day, they behaved toward the object as if they had never previously seen them. This experiment suggests that when removed from the arena for a day, a horse resets its memory and treats the objects in the arena as new.

#### **7. Checking and shying**

The experiments on memory show that horses are motivated to investigate/ check small objects on the ground and they then remember those objects during the period of time that they are in the arena. It is well known that horses shy at novel objects and we reasoned that if we increased the size of the objects, their behavior should transition from investigatory to avoidance behavior. We made round cut outs of cardboard of various sizes and measured approach and avoidance behavior as we rode the horses around the arena. We found that as the size of the object increased, the probability of avoidance behavior increased. This behavior is very similar to that described by Ewart [20] for toads, which approach to eat small objects that he presented to them and who avoided larger objects that he presented, treating them as predators. We also varied the location of the objects in the arena and found that objects were avoided with more vigor at the far end of the arena. Often, an intermediate size object that was avoided at the far end of the arena was investigated at the near end of the arena. Interestingly, the horses were still likely to shy at large objects when returned to the object a short time later. Since their memory for objects in an arena is good, repeated shying appeared unlikely due to poor memory.

#### **8. Discussion**

These experiments tell us two main things about what a horse is thinking when it is taken into an arena. First, the arena is a source of stress and it is likely that it is anxiety provoking. Second, a horse views the arena as a place that is novel and that requires inspection and when not novel a place that must be patrolled and checked. In responding to these two influences, horses display a *spatial gradient* and an *exploratory gradient*. These gradients, if attended to, allow a rider to read the mind of their horse and adjust their ride and their training. We will point out some of the ways that more expert horse handlers show that they are aware of a horse's opinion of an arena to which they are taken.

#### **8.1 The spatial gradient**

**Figure 10** illustrates our model of a horse's spatial view of the world in relation to its actual home, the location of its herd. The model is constructed in the shape of a loop with the base of the loop representing a horse's actual home, its paddock or stall. The blue color of the spectrum of colors in the loop indicates low stress and is associated with the actual home. The color spectrum becomes redder as distance from that home increases to signify an increase in a horse's stress in proportion to the distance from its home. The model is shaped as a loop not only to signify an actual loop but also to signify avoidance of walls or other large objects that will also provoke an increase in stress.

Research on horses in herds that have been together for some time show both that a herd is stable and within the herd social relationships are structured, with horses maintaining favorite relations [21]. Substantial information suggests that that removing an animal from its social group is stressful and remains stressful even after repeated removal [22]. The loop model when superimposed onto an arena explains why the horse chooses the gate area of the area as a home base, why it avoids the walls of the arena, why its movement pattern forms a loop and why it limits its excursion to the near end of the arena. The model also explains why its behavior remains much the same even after attempted adaptation to an arena. It will attempt to confine its activities to the blue regions that are less stressful because they are perceived as closest to its actual home.

On the basis of our model, we have experimented with the idea that when beginning a ride or when warming a horse up for a ride when the horse is alone, a rider mimics the horse's natural behavior. Accordingly, a ride begins with small loops each of which bring the horse back to the starting gate and then extend to include

#### **Figure 10.**

*A model of the spatial gradient. The colored bubble represents a loop pattern of excursion color coded to represent comfort (blue) to anxiety (red). Maximal comfort is in the home paddock and maximum anxiety is at the apex of the loop. When superimposed on the arena the anxiety gradient indicates the entrance, nearest to the paddock, features lowest anxiety and the far end of the arena indicated maximum anxiety.*

**215**

them [26–29].

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse*

more of the arena. On each outward leg of a loop, the horse's anxiety likely increases but then on the return leg to the starting point its anxiety decreases. Over a training session and over days of training, a horse learns that outward excursions will always end with homeward excursions and in this way its behavior becomes managed. A rider might not force a horse down a wall but build up to approaching walls as the

We have seen aspects of our suggestion in play when young horses are first started. Some trainers first halter-break and lead-break a horse when it is in its stall and adapt a horse to a saddle while it is in its stall. We have also observed one horse trainer making the first mount and taking the first ride with horses in their stall. The stall is home and the location of a horse's lowest level of anxiety. Some trainers, when taking a horse to an arena for training might begin the training from the back of another horse. The other horse is a surrogate for its herd and serves to reduce anxiety. A trainer might begin the first ride in arena by making small circles when first asking the horse to move forward under saddle. It is likely that experience has led to training strategies that are integrated into a horse's spatial gradient. The spatial gradient also suggests that any added stress to a horse, including first separation from pair mates or pressure to perform more correctly or quickly, will shift the color gradient in our model from blue to red. It is also likely that when stressed, a horse attributes the stress to the environment and not the handler and so resistance to walls, shying at objects, and moving through the far end of an arena increase in

We have observed handling behaviors that are inconsistent with a horse's spatial gradient. A rider might force a horse to go to the far end of an arena even though it resists. A rider might begin a ride with a horse collected and unable examine the area visually or to examine the ground by sniffing. A handler might take a horse to the center of an arena and lunge it there. Lunging will likely not substitute for arena inspection and object checking. These handling methods might maximize anxiety and result in horse/handler conflict. It is likely that rides taken outside an arena are also subject to the spatial gradient, the further a horse is taken from its paddock, the greater the stress. Many riders taking a horse out alone have experienced the anxiety gradient in a number of ways. If a horse is going to "act up" it is likely this will happen on the outward leg of a trip. A rider might also notice that a horse returns more

The second point raised by our experiments is that each day that a horse is taken to an arena it treats the arena as new. This is not because it does not remember being in the arena or because it does not remember objects in the arena. Rather, it is likely that it wants to ascertain that the arena is safe. Many animal species that maintain home territories patrol and check their territories regularly [24]. It is likely that they want to be certain that the representation that they have of their environment matches the environment. Therefore, to ensure that the arena is safe, a horse needs to sniff the ground and objects in the arena as well as look at them. One clinician explained a horse's display of anxiety as, "there might be a bear there." What could be more threating, however, is the presence of an unknown horse. The many new smells on the ground of the arena, the dropping of another horse left in the arena, are a sign that other horses have been there. Ecological studies of many animal species suggest that daily conspecific aggression is much more likely than is predatory aggression [25]. Previous studies of olfactory memory in horses show that a horse's memory of others is particularly good for horses that have been aggressive toward

*DOI: http://dx.doi.org/10.5772/intechopen.91209*

ride proceeds.

proportion to stress [23].

quickly than it embarks on a ride.

**8.2 The exploratory gradient**

#### *What Are They Thinking? Scientific Horsemanship and the Mind of the Horse DOI: http://dx.doi.org/10.5772/intechopen.91209*

*Equine Science*

**8.1 The spatial gradient**

provoke an increase in stress.

they are perceived as closest to its actual home.

**Figure 10** illustrates our model of a horse's spatial view of the world in relation to its actual home, the location of its herd. The model is constructed in the shape of a loop with the base of the loop representing a horse's actual home, its paddock or stall. The blue color of the spectrum of colors in the loop indicates low stress and is associated with the actual home. The color spectrum becomes redder as distance from that home increases to signify an increase in a horse's stress in proportion to the distance from its home. The model is shaped as a loop not only to signify an actual loop but also to signify avoidance of walls or other large objects that will also

Research on horses in herds that have been together for some time show both that a herd is stable and within the herd social relationships are structured, with horses maintaining favorite relations [21]. Substantial information suggests that that removing an animal from its social group is stressful and remains stressful even after repeated removal [22]. The loop model when superimposed onto an arena explains why the horse chooses the gate area of the area as a home base, why it avoids the walls of the arena, why its movement pattern forms a loop and why it limits its excursion to the near end of the arena. The model also explains why its behavior remains much the same even after attempted adaptation to an arena. It will attempt to confine its activities to the blue regions that are less stressful because

On the basis of our model, we have experimented with the idea that when beginning a ride or when warming a horse up for a ride when the horse is alone, a rider mimics the horse's natural behavior. Accordingly, a ride begins with small loops each of which bring the horse back to the starting gate and then extend to include

*A model of the spatial gradient. The colored bubble represents a loop pattern of excursion color coded to represent comfort (blue) to anxiety (red). Maximal comfort is in the home paddock and maximum anxiety is at the apex of the loop. When superimposed on the arena the anxiety gradient indicates the entrance, nearest to* 

*the paddock, features lowest anxiety and the far end of the arena indicated maximum anxiety.*

**214**

**Figure 10.**

more of the arena. On each outward leg of a loop, the horse's anxiety likely increases but then on the return leg to the starting point its anxiety decreases. Over a training session and over days of training, a horse learns that outward excursions will always end with homeward excursions and in this way its behavior becomes managed. A rider might not force a horse down a wall but build up to approaching walls as the ride proceeds.

We have seen aspects of our suggestion in play when young horses are first started. Some trainers first halter-break and lead-break a horse when it is in its stall and adapt a horse to a saddle while it is in its stall. We have also observed one horse trainer making the first mount and taking the first ride with horses in their stall. The stall is home and the location of a horse's lowest level of anxiety. Some trainers, when taking a horse to an arena for training might begin the training from the back of another horse. The other horse is a surrogate for its herd and serves to reduce anxiety. A trainer might begin the first ride in arena by making small circles when first asking the horse to move forward under saddle. It is likely that experience has led to training strategies that are integrated into a horse's spatial gradient. The spatial gradient also suggests that any added stress to a horse, including first separation from pair mates or pressure to perform more correctly or quickly, will shift the color gradient in our model from blue to red. It is also likely that when stressed, a horse attributes the stress to the environment and not the handler and so resistance to walls, shying at objects, and moving through the far end of an arena increase in proportion to stress [23].

We have observed handling behaviors that are inconsistent with a horse's spatial gradient. A rider might force a horse to go to the far end of an arena even though it resists. A rider might begin a ride with a horse collected and unable examine the area visually or to examine the ground by sniffing. A handler might take a horse to the center of an arena and lunge it there. Lunging will likely not substitute for arena inspection and object checking. These handling methods might maximize anxiety and result in horse/handler conflict. It is likely that rides taken outside an arena are also subject to the spatial gradient, the further a horse is taken from its paddock, the greater the stress. Many riders taking a horse out alone have experienced the anxiety gradient in a number of ways. If a horse is going to "act up" it is likely this will happen on the outward leg of a trip. A rider might also notice that a horse returns more quickly than it embarks on a ride.

#### **8.2 The exploratory gradient**

The second point raised by our experiments is that each day that a horse is taken to an arena it treats the arena as new. This is not because it does not remember being in the arena or because it does not remember objects in the arena. Rather, it is likely that it wants to ascertain that the arena is safe. Many animal species that maintain home territories patrol and check their territories regularly [24]. It is likely that they want to be certain that the representation that they have of their environment matches the environment. Therefore, to ensure that the arena is safe, a horse needs to sniff the ground and objects in the arena as well as look at them. One clinician explained a horse's display of anxiety as, "there might be a bear there." What could be more threating, however, is the presence of an unknown horse. The many new smells on the ground of the arena, the dropping of another horse left in the arena, are a sign that other horses have been there. Ecological studies of many animal species suggest that daily conspecific aggression is much more likely than is predatory aggression [25]. Previous studies of olfactory memory in horses show that a horse's memory of others is particularly good for horses that have been aggressive toward them [26–29].

#### **9. Conclusion**

With this description of our experiments we suggest that a handler can appreciate a horse's thoughts with respect to an arena into which it is taken. In the area, the further a horse goes from the entrance, the greater the stress and the more it will want to leave. Most riders will confirm that even a well-trained horse will need to be encouraged to go into an area and during a ride and will speed up when moving back in the direction of the starting point. Many horses will appear afraid of the far end of the arena and so it will be difficult to get them to go there. Once there, they will not perform as well as they do in the close end of the arena. Many horses will also avoid the wall of the arena and beginning riders may have difficulty getting their horse to stay near the wall when circling an arena. These behaviors are reflected in our model of the horse's spatial gradient. In adapting a horse to an arena, a rider might find that if given the chance, a horse will explore using vision, olfaction, and touch and it will do so each day that it comes to the arena. It has to check or patrol. Allowing a horse to explore might reduce its anxiety by making an arena more like the home paddock. In short, being aware of what a horse is thinking when it is taken out of its paddock to work will improve a horse handling experience as well as improve the chances that the handling experience is accident free. We view the present contribution to scientific based horsemanship as preliminary [30]. There are many aspects of horsemanship that can be further investigated with the arena/home base model, including sex differences, which have only been touched upon here, and genetic [31], developmental [32], and brain influences.

#### **Acknowledgements**

The authors thank Bob McCutcheon for the use of his arena, Cathy Spencer, Meagan Reader, Josh Entz, Heather Holinaty, Bryan Kolb, and Jill West for the use of their horses.

#### **Author details**

Ian Q. Whishaw\* and Candace J. Burke Department of Neuroscience, Canadian Centre for Behavioural Neuroscience, University of Lethbridge, Canada

\*Address all correspondence to: whishaw@uleth.ca

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**217**

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse*

open field: An example of spontaneous episodic memory. Behavioural Brain Research. 2007;**182**(1):119-128

[11] Ainsworth MD. Object relations, dependency, and attachment: A

[12] Harman AM et al. Horse vision and an explanation for the visual behaviour originally explained by the 'ramp retina'. Equine Veterinary Journal.

[13] Pyke GH. Optimal foraging theory: A critical review. Annual Review of Ecology and Systematics.

[14] Fureix C et al. How horses

as significant "objects". Animal Cognition. 2009;**12**(4):643-654

[15] Goodwin D. Equine learning behaviour: What we know, what we don't and future research priorities. Behavioural Processes. 2007;**76**(1):17

[17] Murphy J. Assessing equine prospective memory in a Y-maze apparatus. Veterinary Journal.

[18] Proops L et al. Animals remember previous facial expressions that specific humans have exhibited. Current Biology. 2018;**28**(9):1428-1432.e4

[19] Whishaw IQ, Sacrey LA, Gorny B. Hind limb stepping over obstacles in the horse guided by place-object memory. Behavioural Brain Research.

2009;**181**(1):24-28

2009;**198**(2):372-379

(*Equus caballus*) see the world: Humans

[16] Hanggi EB, Ingersoll JF. Long-term memory for categories and concepts in horses (*Equus caballus*). Animal Cognition. 2009;**12**(3):451-462

1969;**40**(4):969-1025

1999;**31**(5):384-390

1984;**15**(1):523-575

theoretical review of the infant-mother relationship. Child Development.

*DOI: http://dx.doi.org/10.5772/intechopen.91209*

[1] Meredith L et al. Equestrian-related injuries, predictors of fatalities, and the impact on the public health system in Sweden. Public Health. 2019;**168**:67-75

McManus P. A critical review of horserelated risk: A research agenda for safer mounts, riders and equestrian cultures. Animals (Basel). 2015;**5**(3):561-575

[2] Thompson K, McGreevy P,

**References**

[3] Wolyncewicz GEL et al.

2018;**49**(5):933-938

Horse-related injuries in children— Unmounted injuries are more severe: A retrospective review. Injury.

[4] Starling M, McLean A, McGreevy P. The contribution of equitation science to minimising horse-related risks to humans. Animals (Basel). 2016;**6**(3):1-15

"Umwelt": How Living Beings Perceive the World. Berlin: Springer-Verlag; 2008

[6] Budiansky S. The Nature of Horses.

[5] Berthoz A. Neurobiology of

New York: Free Press; 1997

2002;**78**(2):209-224

beproc.2020.104065

1993;**53**(1-2):21-33

[7] Saslow CA. Understanding the perceptual world of horses. Applied Animal Behaviour Science.

[8] Burke C, Whishaw I. Sniff, look and loop excursions as the unit of "exploration" in the horse (*Equus ferus* caballis) when free or under saddle in an Equestrian Arena. Behavioural Processes. 2020:104065. DOI: 10.1016/j.

[9] Golani I, Benjamini Y, Eilam D. Stopping behavior: Constraints on exploration in rats (*Rattus norvegicus*).

[10] Nemati F, Whishaw IQ. The point of entry contributes to the organization of exploratory behavior of rats on an

Behavioural Brain Research.

*What Are They Thinking? Scientific Horsemanship and the Mind of the Horse DOI: http://dx.doi.org/10.5772/intechopen.91209*

#### **References**

*Equine Science*

**9. Conclusion**

**216**

**Author details**

**Acknowledgements**

of their horses.

Ian Q. Whishaw\* and Candace J. Burke

provided the original work is properly cited.

\*Address all correspondence to: whishaw@uleth.ca

University of Lethbridge, Canada

Department of Neuroscience, Canadian Centre for Behavioural Neuroscience,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

upon here, and genetic [31], developmental [32], and brain influences.

The authors thank Bob McCutcheon for the use of his arena, Cathy Spencer, Meagan Reader, Josh Entz, Heather Holinaty, Bryan Kolb, and Jill West for the use

With this description of our experiments we suggest that a handler can appreciate a horse's thoughts with respect to an arena into which it is taken. In the area, the further a horse goes from the entrance, the greater the stress and the more it will want to leave. Most riders will confirm that even a well-trained horse will need to be encouraged to go into an area and during a ride and will speed up when moving back in the direction of the starting point. Many horses will appear afraid of the far end of the arena and so it will be difficult to get them to go there. Once there, they will not perform as well as they do in the close end of the arena. Many horses will also avoid the wall of the arena and beginning riders may have difficulty getting their horse to stay near the wall when circling an arena. These behaviors are reflected in our model of the horse's spatial gradient. In adapting a horse to an arena, a rider might find that if given the chance, a horse will explore using vision, olfaction, and touch and it will do so each day that it comes to the arena. It has to check or patrol. Allowing a horse to explore might reduce its anxiety by making an arena more like the home paddock. In short, being aware of what a horse is thinking when it is taken out of its paddock to work will improve a horse handling experience as well as improve the chances that the handling experience is accident free. We view the present contribution to scientific based horsemanship as preliminary [30]. There are many aspects of horsemanship that can be further investigated with the arena/home base model, including sex differences, which have only been touched

[1] Meredith L et al. Equestrian-related injuries, predictors of fatalities, and the impact on the public health system in Sweden. Public Health. 2019;**168**:67-75

[2] Thompson K, McGreevy P, McManus P. A critical review of horserelated risk: A research agenda for safer mounts, riders and equestrian cultures. Animals (Basel). 2015;**5**(3):561-575

[3] Wolyncewicz GEL et al. Horse-related injuries in children— Unmounted injuries are more severe: A retrospective review. Injury. 2018;**49**(5):933-938

[4] Starling M, McLean A, McGreevy P. The contribution of equitation science to minimising horse-related risks to humans. Animals (Basel). 2016;**6**(3):1-15

[5] Berthoz A. Neurobiology of "Umwelt": How Living Beings Perceive the World. Berlin: Springer-Verlag; 2008

[6] Budiansky S. The Nature of Horses. New York: Free Press; 1997

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[8] Burke C, Whishaw I. Sniff, look and loop excursions as the unit of "exploration" in the horse (*Equus ferus* caballis) when free or under saddle in an Equestrian Arena. Behavioural Processes. 2020:104065. DOI: 10.1016/j. beproc.2020.104065

[9] Golani I, Benjamini Y, Eilam D. Stopping behavior: Constraints on exploration in rats (*Rattus norvegicus*). Behavioural Brain Research. 1993;**53**(1-2):21-33

[10] Nemati F, Whishaw IQ. The point of entry contributes to the organization of exploratory behavior of rats on an

open field: An example of spontaneous episodic memory. Behavioural Brain Research. 2007;**182**(1):119-128

[11] Ainsworth MD. Object relations, dependency, and attachment: A theoretical review of the infant-mother relationship. Child Development. 1969;**40**(4):969-1025

[12] Harman AM et al. Horse vision and an explanation for the visual behaviour originally explained by the 'ramp retina'. Equine Veterinary Journal. 1999;**31**(5):384-390

[13] Pyke GH. Optimal foraging theory: A critical review. Annual Review of Ecology and Systematics. 1984;**15**(1):523-575

[14] Fureix C et al. How horses (*Equus caballus*) see the world: Humans as significant "objects". Animal Cognition. 2009;**12**(4):643-654

[15] Goodwin D. Equine learning behaviour: What we know, what we don't and future research priorities. Behavioural Processes. 2007;**76**(1):17

[16] Hanggi EB, Ingersoll JF. Long-term memory for categories and concepts in horses (*Equus caballus*). Animal Cognition. 2009;**12**(3):451-462

[17] Murphy J. Assessing equine prospective memory in a Y-maze apparatus. Veterinary Journal. 2009;**181**(1):24-28

[18] Proops L et al. Animals remember previous facial expressions that specific humans have exhibited. Current Biology. 2018;**28**(9):1428-1432.e4

[19] Whishaw IQ, Sacrey LA, Gorny B. Hind limb stepping over obstacles in the horse guided by place-object memory. Behavioural Brain Research. 2009;**198**(2):372-379

[20] Ewert JP. Neural mechanisms of prey-catching and avoidance behavior in the toad (*Bufo bufo* L.). Brain, Behavior and Evolution. 1970;**3**(1):36-56

[21] Hauschildt V, Gerken M. Temporal stability of social structure and behavioural synchronization in Shetland pony mares (*Equus caballus*) kept on pasture. Acta Agriculturae Scandinavica, Section A—Animal Science. 2015;**65**(1):33-41

[22] Senst L et al. Sexually dimorphic neuronal responses to social isolation. eLife. 2016;**5**:218726

[23] Hausberger M et al. Mutual interactions between cognition and welfare: The horse as an animal model. Neuroscience and Biobehavioral Reviews. 2019;**107**:540-559

[24] Spencer WD. Home ranges and the value of spatial information. Journal of Mammalogy. 2012;**93**(4):929-947

[25] Whishaw IQ, Whishaw GE. Conspecific aggression influences food carrying: Studies on a wild population of *Rattus norvegicus*. Aggressive Behavior. 1996;**22**(1):47-66

[26] Krueger K, Flauger B. Olfactory recognition of individual competitors by means of faeces in horse (*Equus caballus*). Animal Cognition. 2011;**14**(2):245-257

[27] Peron F, Ward R, Burman O. Horses (*Equus caballus*) discriminate body odour cues from conspecifics. Animal Cognition. 2014;**17**(4):1007-1011

[28] Feist JD, McCullough DR. Behavior patterns and communication in feral horses. Zeitschrift für Tierpsychologie. 1976;**41**(4):337-371

[29] McDonnell SM. Reproductive behavior of stallions and mares: Comparison of free-running and domestic in-hand breeding.

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[20] Ewert JP. Neural mechanisms of prey-catching and avoidance behavior in the toad (*Bufo bufo* L.). Brain, Behavior

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[31] Burns E, Enns R, Garrick D. The status of equine genetic evaluation. In: Proceedings-American Society of Animal Science Western Section. 2004

Walter KW. Horse species symposium: Nutritional programming and the impact on mare and foal performance.

[32] Coverdale JA, Hammer CJ,

Journal of Animal Science. 2015;**93**(7):3261-3267

2000;**60-61**:211-219

2007;**174**(3):492-500

[21] Hauschildt V, Gerken M. Temporal stability of social structure and behavioural synchronization in Shetland pony mares (*Equus caballus*) kept on pasture. Acta Agriculturae Scandinavica, Section A—Animal

[22] Senst L et al. Sexually dimorphic neuronal responses to social isolation.

[24] Spencer WD. Home ranges and the value of spatial information. Journal of Mammalogy. 2012;**93**(4):929-947

[23] Hausberger M et al. Mutual interactions between cognition and welfare: The horse as an animal model. Neuroscience and Biobehavioral Reviews. 2019;**107**:540-559

[25] Whishaw IQ, Whishaw GE. Conspecific aggression influences food carrying: Studies on a wild population of *Rattus norvegicus*. Aggressive Behavior. 1996;**22**(1):47-66

[26] Krueger K, Flauger B. Olfactory recognition of individual competitors by means of faeces in horse (*Equus caballus*). Animal Cognition.

[27] Peron F, Ward R, Burman O. Horses (*Equus caballus*) discriminate body odour cues from conspecifics. Animal Cognition. 2014;**17**(4):1007-1011

[28] Feist JD, McCullough DR. Behavior patterns and communication in feral horses. Zeitschrift für Tierpsychologie.

[29] McDonnell SM. Reproductive behavior of stallions and mares: Comparison of free-running and domestic in-hand breeding.

2011;**14**(2):245-257

1976;**41**(4):337-371

and Evolution. 1970;**3**(1):36-56

Science. 2015;**65**(1):33-41

eLife. 2016;**5**:218726

### *Edited by Catrin Rutland and Albert Rizvanov*

Understanding the latest developments in equine science is essential for all veterinary and equine professionals and students, researchers, owners, and those caring for equids. This book reflects the diversity in research presently being carried out worldwide. From locomotion and the digestive system, through to the skin and reproduction. The chapter on medicine includes not only some of the latest advances in gene therapy but also reveals medieval treatments, providing a fascinating glimpse into the past whilst also looking at future technologies. The book also highlights some contemporary insights into diet and behavior. From DNA and individual cells through to the entire animal, this research uses different scientific methods to understand horses and donkeys in greater detail.

Published in London, UK © 2020 IntechOpen © RosaFrei / iStock

Equine Science

IntechOpen Book Series

Veterinary Medicine and Science, Volume 5

Equine Science

*Edited by Catrin Rutland and Albert Rizvanov*