**5. Nutrition and secretory immune response**

The GIT is an extremely expensive tissue in terms of energy and nutrient needs to maintain and facilitate the full range of barrier and energy/nutrient assimilation functions it displays. Cant et al. [113] estimated that the GIT consumes approximately 20% of dietary energy with a turn-over rate of 50 to 75% per day. However, the GIT is a dynamic organ system whose maintenance needs dramatically changes based on responsive demands. Applegate [114] elucidated some of these adaptive responses, including: changes to peristaltic rate, changes to enterocyte turnover, tight junction regulation, mucin production (quantity and composition), changes to differentiation direction of undifferentiated cells and changes to secretory defenses.

While we often think of presence of microbiota as an additional barrier cost, there is some symbiotic relationships that they convey to the host. For example, the presence of the ceca contributes approximately 3% to dry matter digestibility to the bird [115] in part through 8% of energy derived from microbial fermentation resulting in short-chain fatty acids [116, 117].

Due to limitations of space in this review, we were unable to address all nutrient impacts on the secretory immune defenses of the bird. Notably, recent reviews have published on roles of amino acids on physiological, immunological, and microbiological responses as well as quantification of changes to endogenous amino acid production in the bird [118, 119]; as well as implications of protein indigestibility in

*Advances in Poultry Nutrition Research*

less prominent CD8+ cell population [86].

epithelial cells [90, 94, 95].

rial colonization [101].

Moreover, within the CD8+ IEL population the majority express CD8αα homodimers rather than the CD8αβ heterodimer commonly expressed on classical CD8+ T cells found at systemic sites [83–85]. The proportions of IEL belonging to each subpopulation differ according to age, genetics and environment (including infection). Numerically, B and T cells are the most common lymphocytes (~90%), the remainder being of the NK cell phenotype (CD3-Bu-1-). In contrast to the IEL population, the T cell population of the lamina propria contains a smaller proportion of γδ-T cells (~10%); the much larger αβ-T cell population is dominated by CD4+ T cells, with a

**4.1 Secretory IgA (sIgA) and its transporter, polymeric Ig receptor (pIgR)**

The existence of sIgA in the bird has been established for quite some time, but studies are relatively limited compared with mammals. In humans, it is estimated that approximately 70% of the body's IgA-producing plasma cells (differentiated from activated B cells) reside in the lamina propria of intestinal mucosa [87–89]. Although sIgA belongs to adaptive immunity by definition, it plays an important role in the first lines of mucosal defense [87, 90]. There are three modes of defense modulated by sIgA on gut mucosal surfaces: (1) sIgA has been shown to interfere with the early steps of the infection process through directly blocking pathogens and toxins from attaching to the intestinal epithelium [91]; (2) sIgA exerts the protective immunity through immune exclusion, which is the prevention of pathogens and toxins from approaching to epithelium through the stepwise procedures involving antibody-mediated agglutination, entrapment in mucus, and clearance through intestine peristalsis [92, 93]; (3) sIgA exhibits the ability to neutralize intracellular pathogens, viruses, and toxins within intestinal epithelial cells, which requires binding of specific IgA and occupation of antigens by pIgR transportation vesicles, followed by the passage of antigens into the lumen. Notably, the intracellular neutralization of LPS by IgA indicates the potential role in anti-inflammation and deactivation of the proinflammatory pathways in

T-cells generally produce high-affinity IgA antibodies. IgA has the specificity against previous exposure of the GIT by pathogens and more invasive commensal species [89, 96]. Conversely, low-affinity IgA antibodies can also be produced from T-cell-independent (TI) pathways. These low-affinity IgA antibodies act through coating commensal bacteria thereby augmenting the competitive inhibition of pathogens [88, 89, 96]. The production of both high and low-affinity production of IgA provides protective roles during an overt infection with a pathogen as well as

Presence of microflora in the the GIT may also regulate production of IgA. Studies with germ-free mice [99] and pigs [100, 101] have demonstrated that intestinal IgA and IgA-positive cells in the lamina propria are dramatically reduced versus conventionally reared animals. Further studies have shown that specific microflora (e.g. segmented filamentous bacteria and clostridia) when given to germ-free mice will stimulate the development of IgA-producing cells, while other microflora will have no effect or inhibit this development [97, 98]. Thus, other researchers have reported similar IgA production responses with poultry diets were supplemented with probiotics [99, 100]. Notably, IgA development in the hindgut of the bird early in life coincides with the rapidity of bacte-

Prior to development of IgA by the GIT, the chick is reliant upon maternal antibodies and physical defenses (such as mucins and intestinal turnover). In birds, a small amount of IgA (~ 0.3 mg) is transferred via the embryo imbibing amniotic

during unchallenged/non-pathogenic bacterial exposure.

**126**

the GIT and implications of microbial fermentation of protein in the hindgut of the animal [120]. Additional impact of microminerals (e.g. zinc, copper, and manganese) and plant bioactive compounds on intestinal functionality have been elucidated [121, 122]. Similarly, recent research has revealed modes of action of specific classes of feed additives that directly or indirectly influence the secretory immune responses of the GIT. For example, probiotic and phytogenic additives have had numerous reviews on these actions [123–125]. Further elucidation of contribution of specific fibrous and fatty acids to the intestinal secretory defenses are further elucidated.

#### **5.1 Dietary fiber and intestinal health**

Carbohydrates that are not hydrolyzed by endogenous enzymes in the upper GIT can be fermented by bacteria in the large intestine and ceca are designated as dietary fiber [126]. Dietary fiber (DF) resides in the indigestible portion of plant derived foods that include cell walls, non-starch polysaccharides (NSP), oligosaccharides and lignin [126, 127].

Polysaccharides of NSP include cellulose, pectins, β-glucans, pentosans, heteroxylans and xyloglucan [128]. There are two different types of NSP, soluble and insoluble. Such classification is based on their solubility in water. The ability of soluble NSP to mix with water, producing an increase in the viscosity of the digesta and decreasing the binding of digestive enzymes, negatively affects the digestibility of nutrients [129]. As a result of suboptimal digestion, there is an increase in GIT surface area and secretion of digestive enzymes, creating an increased endogenous energy cost of digestion and affecting bird productivity [130]. NSP from cerealbased diets are associated with low apparently metabolized energy, increased feed conversion rates and increased incidence of wet droppings.

Some previous studies have considered the effects of different cereal NSP based diets on the intestinal microbial immunity. Different types of cereal can modify specific members of the microbiota in the cecum of chickens in two different ways; by altering the viscosity and pH and/or by supplying nutrients to produce the selective growth of specific bacteria [131]. The increase in digesta viscosity with the subsequent reduction in feed passage rate leaves more undigestible feed in the intestine, which represents an ideal substrate for bacterial growth [131]. Chickens fed with a barley-based diet had a higher number of *Clostridium perfringens* in the ileum and ceca. Likewise, it has been reported that the use of wheat in poultry diets may favor the proliferation of pathogenic bacteria like *Escherichia coli*, Salmonella and Campylobacter [132].

In contrast, insoluble NSP is metabolized into short chain fatty acids (SCFA) including acetate, propionate, butyrate, valerate and isovalerate [116]. Those fermentable metabolites serve as sources of carbon and energy for the commensal microbiota in the lower intestine, specifically, for the bacterial population in the ceca of chickens [116] which provide up to 10% of the energy to the bird. In addition, cecal reverse peristalsis produces translocation of the cecal microbiota affecting energy metabolism and performance [133]. The fermentation metabolites produced by the intestinal bacteria depends on the availability of the substrate, fermentation mechanisms and bacteria specie involved in the process [117].

Dietary fiber has a direct, positive effect on the immune response in numerous species by increasing the abundance of some immune cells, specifically T cells, in the gut-associated lymphoid tissue [134], changing the cytokine secretion profile [135, 136] increasing mucosal immunoglobulins and by acting as a prebiotic substrate for beneficial bacteria [137]. For feed ingredients to be considered prebiotics,

**129**

associated mortality [152].

*Secretory Defense Response in the Bird's Gastro-Intestinal Tract and Nutritional Strategies…*

they have to meet the following criteria: resistance to an acidic environment (indigestible), fermentation by intestinal microbiota and selective stimulation of beneficial bacterial populations [138]. Based on this concept, dietary fiber is classi-

function including direct production of SCFA [139, 140], augmentation of gut burrier function [141], influence on immune mediated inflammatory responses and

In human nutrition, multiple benefits have been attributed to dietary fiber, including maintaining normal bowel structure and function, increasing water retention, blood flow, fluid, and electrolyte uptake in colonic intestinal mucosa [128, 142]. Moreover, fiber intake can reduce the risk of metabolic diseases such as obesity, coronary artery disease, diabetes, constipation, inflammatory bowel disease, colitis and colon cancer [128]. In diets rich in protein, the inclusion of dietary fiber such as arabinoxylan-oligosaccharides (AXOS) can potentially decrease the generation of toxic metabolites originated from proteolytic activity and increase the

The addition of dietary fiber has also been widely adopted in swine nutrition in order to maximize the nutrient supply and intestinal health [144, 145]. Dietary fiber can change the physiological features of the digesta, most notably modifying the transit time, and the composition of digesta in terms of solubility, fermentability and water retention. Such changes have a direct impact on intestinal functions, bacteria population and fermentation. The inclusion of high to moderate levels of dietary fiber in pigs, remodel the gut microbiota since certain healthy bacteria species such as Lactobacilli and Bifidobacterium tend to increase. The proliferation of lactic acid producing bacteria decrease the pH of the intestinal lumen, resulting in decreased abundance of other pH sensitive enteropathogenic bacteria like *Escherichia coli*, Salmonella, Shigella and Clostridia [144, 145]. Other effects of dietary fiber have been demonstrated. Changes in the gut morphology, most remarkably inducing increases in crypt depth and altering cell division in growing pigs. This effect has been attributed to the trophic nature of SCFA, specifically butyrate [145]. In contrast, fiber is a feed ingredient poorly utilized in poultry nutrition due to antinutritional effects observed from soluble fiber sources that are mainly associated with increased viscosity of digesta and subsequent impair of nutrient absorption and performance parameters [129]. The effects of fiber are variable and depends on the fiber source, particle size, level of inclusion and chemical composition [146]. A number of studies have found that low levels of insoluble fiber can provide benefits from the point of view of gut health by improving nutrient digestibility [147], gizzard functionality, and resulting in modulation of digesta passage and higher nutrient retention [148, 149]. In the literature, a wide range of other effects of dietary fiber have been demonstrated in laying breeders and broilers chickens. In commercial layers supplemented with high fiber ingredients in the diets, environmental improvements have been demonstrated by reducing ammonia concentrations in manure [150], feather pecking [151], cannibalistic behavior and

A number of oligosaccharides including lactulose, inulin, galacto-oligosaccharide and mannan oligosaccharides have been proposed to use as prebiotics in chickens. Those non-digestible carbohydrates are metabolized by fermenting bacteria to produce SCFAs. SCFA are nutritional substrates required for an adequate function of the immune system [139]. When xylo-oligosaccharides were supplemented into a broiler chicken diet, the abundance of butyrate-producing bacteria in the colon and ceca, such as Bifidobacterium and Lactobacillus, significantly increased [153].

restoration of the physiological function of bacterial populations.

amount of health-promoting bacterial populations [143].

A number of studies have found that fiber-rich prebiotics can enhance immune

*DOI: http://dx.doi.org/10.5772/intechopen.95952*

fied as a prebiotic.

#### *Secretory Defense Response in the Bird's Gastro-Intestinal Tract and Nutritional Strategies… DOI: http://dx.doi.org/10.5772/intechopen.95952*

they have to meet the following criteria: resistance to an acidic environment (indigestible), fermentation by intestinal microbiota and selective stimulation of beneficial bacterial populations [138]. Based on this concept, dietary fiber is classified as a prebiotic.

A number of studies have found that fiber-rich prebiotics can enhance immune function including direct production of SCFA [139, 140], augmentation of gut burrier function [141], influence on immune mediated inflammatory responses and restoration of the physiological function of bacterial populations.

In human nutrition, multiple benefits have been attributed to dietary fiber, including maintaining normal bowel structure and function, increasing water retention, blood flow, fluid, and electrolyte uptake in colonic intestinal mucosa [128, 142]. Moreover, fiber intake can reduce the risk of metabolic diseases such as obesity, coronary artery disease, diabetes, constipation, inflammatory bowel disease, colitis and colon cancer [128]. In diets rich in protein, the inclusion of dietary fiber such as arabinoxylan-oligosaccharides (AXOS) can potentially decrease the generation of toxic metabolites originated from proteolytic activity and increase the amount of health-promoting bacterial populations [143].

The addition of dietary fiber has also been widely adopted in swine nutrition in order to maximize the nutrient supply and intestinal health [144, 145]. Dietary fiber can change the physiological features of the digesta, most notably modifying the transit time, and the composition of digesta in terms of solubility, fermentability and water retention. Such changes have a direct impact on intestinal functions, bacteria population and fermentation. The inclusion of high to moderate levels of dietary fiber in pigs, remodel the gut microbiota since certain healthy bacteria species such as Lactobacilli and Bifidobacterium tend to increase. The proliferation of lactic acid producing bacteria decrease the pH of the intestinal lumen, resulting in decreased abundance of other pH sensitive enteropathogenic bacteria like *Escherichia coli*, Salmonella, Shigella and Clostridia [144, 145]. Other effects of dietary fiber have been demonstrated. Changes in the gut morphology, most remarkably inducing increases in crypt depth and altering cell division in growing pigs. This effect has been attributed to the trophic nature of SCFA, specifically butyrate [145]. In contrast, fiber is a feed ingredient poorly utilized in poultry nutrition due to antinutritional effects observed from soluble fiber sources that are mainly associated with increased viscosity of digesta and subsequent impair of nutrient absorption and performance parameters [129]. The effects of fiber are variable and depends on the fiber source, particle size, level of inclusion and chemical composition [146]. A number of studies have found that low levels of insoluble fiber can provide benefits from the point of view of gut health by improving nutrient digestibility [147], gizzard functionality, and resulting in modulation of digesta passage and higher nutrient retention [148, 149]. In the literature, a wide range of other effects of dietary fiber have been demonstrated in laying breeders and broilers chickens. In commercial layers supplemented with high fiber ingredients in the diets, environmental improvements have been demonstrated by reducing ammonia concentrations in manure [150], feather pecking [151], cannibalistic behavior and associated mortality [152].

A number of oligosaccharides including lactulose, inulin, galacto-oligosaccharide and mannan oligosaccharides have been proposed to use as prebiotics in chickens. Those non-digestible carbohydrates are metabolized by fermenting bacteria to produce SCFAs. SCFA are nutritional substrates required for an adequate function of the immune system [139]. When xylo-oligosaccharides were supplemented into a broiler chicken diet, the abundance of butyrate-producing bacteria in the colon and ceca, such as Bifidobacterium and Lactobacillus, significantly increased [153].

*Advances in Poultry Nutrition Research*

**5.1 Dietary fiber and intestinal health**

charides and lignin [126, 127].

and Campylobacter [132].

elucidated.

the GIT and implications of microbial fermentation of protein in the hindgut of the animal [120]. Additional impact of microminerals (e.g. zinc, copper, and manganese) and plant bioactive compounds on intestinal functionality have been elucidated [121, 122]. Similarly, recent research has revealed modes of action of specific classes of feed additives that directly or indirectly influence the secretory immune responses of the GIT. For example, probiotic and phytogenic additives have had numerous reviews on these actions [123–125]. Further elucidation of contribution of specific fibrous and fatty acids to the intestinal secretory defenses are further

Carbohydrates that are not hydrolyzed by endogenous enzymes in the upper GIT can be fermented by bacteria in the large intestine and ceca are designated as dietary fiber [126]. Dietary fiber (DF) resides in the indigestible portion of plant derived foods that include cell walls, non-starch polysaccharides (NSP), oligosac-

Polysaccharides of NSP include cellulose, pectins, β-glucans, pentosans, heteroxylans and xyloglucan [128]. There are two different types of NSP, soluble and insoluble. Such classification is based on their solubility in water. The ability of soluble NSP to mix with water, producing an increase in the viscosity of the digesta and decreasing the binding of digestive enzymes, negatively affects the digestibility of nutrients [129]. As a result of suboptimal digestion, there is an increase in GIT surface area and secretion of digestive enzymes, creating an increased endogenous energy cost of digestion and affecting bird productivity [130]. NSP from cerealbased diets are associated with low apparently metabolized energy, increased feed

Some previous studies have considered the effects of different cereal NSP based diets on the intestinal microbial immunity. Different types of cereal can modify specific members of the microbiota in the cecum of chickens in two different ways; by altering the viscosity and pH and/or by supplying nutrients to produce the selective growth of specific bacteria [131]. The increase in digesta viscosity with the subsequent reduction in feed passage rate leaves more undigestible feed in the intestine, which represents an ideal substrate for bacterial growth [131]. Chickens fed with a barley-based diet had a higher number of *Clostridium perfringens* in the ileum and ceca. Likewise, it has been reported that the use of wheat in poultry diets may favor the proliferation of pathogenic bacteria like *Escherichia coli*, Salmonella

In contrast, insoluble NSP is metabolized into short chain fatty acids (SCFA) including acetate, propionate, butyrate, valerate and isovalerate [116]. Those fermentable metabolites serve as sources of carbon and energy for the commensal microbiota in the lower intestine, specifically, for the bacterial population in the ceca of chickens [116] which provide up to 10% of the energy to the bird. In addition, cecal reverse peristalsis produces translocation of the cecal microbiota affecting energy metabolism and performance [133]. The fermentation metabolites produced by the intestinal bacteria depends on the availability of the substrate, fermentation mechanisms and bacteria specie involved in the process [117].

Dietary fiber has a direct, positive effect on the immune response in numerous species by increasing the abundance of some immune cells, specifically T cells, in the gut-associated lymphoid tissue [134], changing the cytokine secretion profile [135, 136] increasing mucosal immunoglobulins and by acting as a prebiotic substrate for beneficial bacteria [137]. For feed ingredients to be considered prebiotics,

conversion rates and increased incidence of wet droppings.

**128**

Similarly, Zhao et al. reported an increase in Lactobacillus counts in excreta when birds were fed with 0.15% inclusion of lactulose [154].

Production of butyrate is considered advantageous to maintain gut health. Butyrate is an important energy source for the enterocytes [140] and is characterized for having immunomodulatory properties. Butyrate can have an anti-inflammatory effect by modulating key inflammatory mediators including the reduction of IFN-γ and NF-kB and the increase in the number of T reg cells and the expression of IL-10 which suppresses the activity of the immune system [155]. Likewise, inulin supplementation in broiler chickens (0.25-0.5%) induces an anti-inflammatory response by decreasing the gene expression of proinflammatory cytokines such as NF-kB, LITAF, IL-6, iNOS and enhances the protective barrier function represented by increased expression of epithelial tightness components including MUC2 and claudin-1 [156].

Other major effects have been shown with the supplementation of oligosaccharides, such as the improvement of growth performance [153], the influence on the intestinal morphology reflected in an increase in crypt depth, villus height and villus area [157] and the reduction of pathogenic bacterial colonization. The increase in pathogen resistance due to prebiotic supplementation is associated with the simultaneous elevation of lactic acid producing bacteria and the decrease in the pH of the intestinal lumen, creating an unfavorable environment for pathogenic bacteria and thereby decreasing the colonization. In fact, a meta-analysis study showed a reduction of 0.61 log10 cfu/g cecal Salmonella spp. in birds treated with lactose and its associated prebiotic products (lactulose, lacto-sucrose, whey and dried milk) [158].

#### **5.2 Fatty acids and immune response**

Short-chain and medium chain fatty acids play an important role on maintaining intestinal gut health and controlling enteric pathogens [159]. Endogenous metabolic pathways, including beta oxidation of fats, leads to the production of short chain fatty acids (SCFA) such as acetate, propionate and butyrate [160]. Long chain fatty acids can be converted into acetate via acetyl-coA or in propionate via propionyl-CoA [160]. SCFA can modulate multiple cellular metabolic activities by the interaction of nuclear cellular (G-protein couple receptors: GRPs), enzymatic receptors (histone deacetylases: HDACs), serving as a substrate for energy for enterocyte and Krebs's cycle and inducing apoptosis of cells [156]. Through these mechanisms, SCFA modulates gene transcription of cells involved in metabolic pathways, inflammation and immune response. In intestinal cells, butyrate and propionate has the ability to inhibit the HDAC activity which decrease the activation of NFkB transcription factor and subsequently modulating the expression of inflammatory genes [161]. The anti-inflammatory effect of butyrate is produced by preventing the secretion of pro-inflammatory cytokines by macrophages through the NFkb pathway [156].

Regarding the adaptive immune response, butyrate plays an important role in modifying various lymphocyte function including the inhibition of T-cell proliferation, and reduction of the secretion of pro-inflammatory cytokines such as IL-2, IFN-γ and promoting the production of the main anti-inflammatory cytokine, IL-10 [156, 161].

Due to its anti-inflammatory properties, SCFA has been used as a therapeutic alternative for intestinal diseases [162]. Direct delivery of SCFA by encapsulation allows the supplementation without the need for fermentation, increasing the release in the distal gastrointestinal section [163]. Multiple studies have shown that SCFAs are beneficial as a drinking water supplement and feed additive for the control of Salmonella, Campylobacter and Clostridium [164, 165].

In young chickens, *Salmonella enterica spp. enteritidis* cecal colonization significantly decreased when butyric acid was added to the feed [166, 167]. The

**131**

inflammatory diseases.

**6. Conclusions**

*Secretory Defense Response in the Bird's Gastro-Intestinal Tract and Nutritional Strategies…*

broiler chickens by reducing C. jejuni counts in the crop [173].

Among different classes of fatty acids, medium chain fatty acids (MCFA) have reported to be more inhibitory against Salmonella than short chain fatty acids [163]. MCFA are fatty acids composed by 6 to 12 carbons and include caproic, caprylic, capric and lauric fatty acids [174]. The greater antibacterial effect of MCFA is corelated with metabolic differences. Because of its smaller molecular size, MCFA can be absorbed more efficiently and therefore can be utilized more efficiently in the intestinal tract [175]. Indeed, the in-vitro antimicrobial activity of MCFA against Salmonella is observed at very low concentrations (between 10 nM- 50 nM) [176, 177]. Furthermore, in-vivo studies have shown reduction in Salmonella cecal counts with supplementation of caprylic acid [178, 179]. The supplementation with either 0.7 or 1% of caprylic acid significantly reduced the *Salmonella enterica spp. enteritidis* counts in cecal samples of birds fed caprylic acid 7 to 10 days post-challenge in 18 day-old chickens [179]. Another study, showed a reduction in cecal Salmonella *Salmonella enterica spp. enteritidis* counts in ceca, spleen and liver [178] in 3 and 6-week-old chickens. Similarly, the supplementation of caproic acid in broilers decrease the colonization of Salmonella through hilA gen suppression [177].

MCFA acid have also been used for controlling Campylobacter jejuni. Although, studies have shown inconsistent results, caprylic acid at 0.7 and 1.4% has shown to be effective in reducing C. jejuni counts by 3 to 5 log in infected chickens [180]. In conclusion, the application of fatty acids to reduce inflammation and intestinal pathogens is an alternative strategy for poultry nutritionists. Multiple studies support the important role of fatty acids as a modulation of intestinal health. Long chain fatty acids can modulate innate and adaptive immune responses and reduce inflammation produced by systemic diseases. On the other hand, SCFA and MCFA modulate the immune cell function to facilitate the elimination of pathogenic bacteria. Understanding the role of fatty acids in health and disease will increase the effectiveness of these compounds in a wide range of intestinal, metabolic and

In summary, secretory defense host response and their players including host defense peptides, sIgA and pIgR among others, constitute the first line of intestinal

addition of SCFA in the drinking water has also been used as an efficient strategy for decreasing the recovery of *Salmonella enterica spp. typhimurium* in the crop and in pre-chilled carcasses at the processing plant [168]. The reduction in colonization of Salmonella by SCFA is related to the regulation of invasion genes (hilA, invF and sipC) located on the pathogenicity island (Sp1-1) [169]. In addition to the antimicrobial activity, SCFA can contribute to disease resistance by enhancing the expression of host defense peptides including Avian β-defensin 9 (*AvBD9*), *cathelicidin B1*, *AvBD3*, *AvBD4*, *AvBD8*, *AvBD10* and *AvBD14* which consequently reduce bacterial growth [170]. However, the ability of SCFA to control Salmonella is highly correlated with acid type and concentration. For example, the feed supplementation of butyric acid in the coated form is more effective in decreasing *Salmonella enterica spp. enteritidis* counts than when using the powder form [166]. Previous studies have also investigated the formic-propionic acid combination at 0.5 and 0.68% respectively, with a significant reduction of *Salmonella enterica spp. kedougou* [171]. Furthermore, the use of a combination of propionic and formic acid decreased the recovery of *Salmonella enterica spp. typhimurium* in the ceca by 3.61 log at 21 days [172]. Similarly, the combination of 1.5% of formic acid and 0.1% of sorbic acid were protective against Campylobacter jejuni colonization during infection trials in

*DOI: http://dx.doi.org/10.5772/intechopen.95952*

*Secretory Defense Response in the Bird's Gastro-Intestinal Tract and Nutritional Strategies… DOI: http://dx.doi.org/10.5772/intechopen.95952*

addition of SCFA in the drinking water has also been used as an efficient strategy for decreasing the recovery of *Salmonella enterica spp. typhimurium* in the crop and in pre-chilled carcasses at the processing plant [168]. The reduction in colonization of Salmonella by SCFA is related to the regulation of invasion genes (hilA, invF and sipC) located on the pathogenicity island (Sp1-1) [169]. In addition to the antimicrobial activity, SCFA can contribute to disease resistance by enhancing the expression of host defense peptides including Avian β-defensin 9 (*AvBD9*), *cathelicidin B1*, *AvBD3*, *AvBD4*, *AvBD8*, *AvBD10* and *AvBD14* which consequently reduce bacterial growth [170]. However, the ability of SCFA to control Salmonella is highly correlated with acid type and concentration. For example, the feed supplementation of butyric acid in the coated form is more effective in decreasing *Salmonella enterica spp. enteritidis* counts than when using the powder form [166]. Previous studies have also investigated the formic-propionic acid combination at 0.5 and 0.68% respectively, with a significant reduction of *Salmonella enterica spp. kedougou* [171]. Furthermore, the use of a combination of propionic and formic acid decreased the recovery of *Salmonella enterica spp. typhimurium* in the ceca by 3.61 log at 21 days [172]. Similarly, the combination of 1.5% of formic acid and 0.1% of sorbic acid were protective against Campylobacter jejuni colonization during infection trials in broiler chickens by reducing C. jejuni counts in the crop [173].

Among different classes of fatty acids, medium chain fatty acids (MCFA) have reported to be more inhibitory against Salmonella than short chain fatty acids [163]. MCFA are fatty acids composed by 6 to 12 carbons and include caproic, caprylic, capric and lauric fatty acids [174]. The greater antibacterial effect of MCFA is corelated with metabolic differences. Because of its smaller molecular size, MCFA can be absorbed more efficiently and therefore can be utilized more efficiently in the intestinal tract [175]. Indeed, the in-vitro antimicrobial activity of MCFA against Salmonella is observed at very low concentrations (between 10 nM- 50 nM) [176, 177]. Furthermore, in-vivo studies have shown reduction in Salmonella cecal counts with supplementation of caprylic acid [178, 179]. The supplementation with either 0.7 or 1% of caprylic acid significantly reduced the *Salmonella enterica spp. enteritidis* counts in cecal samples of birds fed caprylic acid 7 to 10 days post-challenge in 18 day-old chickens [179]. Another study, showed a reduction in cecal Salmonella *Salmonella enterica spp. enteritidis* counts in ceca, spleen and liver [178] in 3 and 6-week-old chickens. Similarly, the supplementation of caproic acid in broilers decrease the colonization of Salmonella through hilA gen suppression [177].

MCFA acid have also been used for controlling Campylobacter jejuni. Although, studies have shown inconsistent results, caprylic acid at 0.7 and 1.4% has shown to be effective in reducing C. jejuni counts by 3 to 5 log in infected chickens [180].

In conclusion, the application of fatty acids to reduce inflammation and intestinal pathogens is an alternative strategy for poultry nutritionists. Multiple studies support the important role of fatty acids as a modulation of intestinal health. Long chain fatty acids can modulate innate and adaptive immune responses and reduce inflammation produced by systemic diseases. On the other hand, SCFA and MCFA modulate the immune cell function to facilitate the elimination of pathogenic bacteria. Understanding the role of fatty acids in health and disease will increase the effectiveness of these compounds in a wide range of intestinal, metabolic and inflammatory diseases.

#### **6. Conclusions**

In summary, secretory defense host response and their players including host defense peptides, sIgA and pIgR among others, constitute the first line of intestinal

*Advances in Poultry Nutrition Research*

**5.2 Fatty acids and immune response**

birds were fed with 0.15% inclusion of lactulose [154].

Similarly, Zhao et al. reported an increase in Lactobacillus counts in excreta when

Production of butyrate is considered advantageous to maintain gut health. Butyrate is an important energy source for the enterocytes [140] and is characterized for having immunomodulatory properties. Butyrate can have an anti-inflammatory effect by modulating key inflammatory mediators including the reduction of IFN-γ and NF-kB and the increase in the number of T reg cells and the expression of IL-10 which suppresses the activity of the immune system [155]. Likewise, inulin supplementation in broiler chickens (0.25-0.5%) induces an anti-inflammatory response by decreasing the gene expression of proinflammatory cytokines such as NF-kB, LITAF, IL-6, iNOS and enhances the protective barrier function represented by increased expression of epithelial tightness components including MUC2 and claudin-1 [156]. Other major effects have been shown with the supplementation of oligosaccharides, such as the improvement of growth performance [153], the influence on the intestinal morphology reflected in an increase in crypt depth, villus height and villus area [157] and the reduction of pathogenic bacterial colonization. The increase in pathogen resistance due to prebiotic supplementation is associated with the simultaneous elevation of lactic acid producing bacteria and the decrease in the pH of the intestinal lumen, creating an unfavorable environment for pathogenic bacteria and thereby decreasing the colonization. In fact, a meta-analysis study showed a reduction of 0.61 log10 cfu/g cecal Salmonella spp. in birds treated with lactose and its associated prebiotic products (lactulose, lacto-sucrose, whey and dried milk) [158].

Short-chain and medium chain fatty acids play an important role on maintaining intestinal gut health and controlling enteric pathogens [159]. Endogenous metabolic pathways, including beta oxidation of fats, leads to the production of short chain fatty acids (SCFA) such as acetate, propionate and butyrate [160]. Long chain fatty acids can be converted into acetate via acetyl-coA or in propionate via propionyl-CoA [160]. SCFA can modulate multiple cellular metabolic activities by the interaction of nuclear cellular (G-protein couple receptors: GRPs), enzymatic receptors (histone deacetylases: HDACs), serving as a substrate for energy for enterocyte and Krebs's cycle and inducing apoptosis of cells [156]. Through these mechanisms, SCFA modulates gene transcription of cells involved in metabolic pathways, inflammation and immune response. In intestinal cells, butyrate and propionate has the ability to inhibit the HDAC activity which decrease the activation of NFkB transcription factor and subsequently modulating the expression of inflammatory genes [161]. The anti-inflammatory effect of butyrate is produced by preventing the secretion of pro-inflammatory cytokines by macrophages through the NFkb pathway [156]. Regarding the adaptive immune response, butyrate plays an important role in modifying various lymphocyte function including the inhibition of T-cell proliferation, and reduction of the secretion of pro-inflammatory cytokines such as IL-2, IFN-γ and promoting the production of the main anti-inflammatory cytokine,

Due to its anti-inflammatory properties, SCFA has been used as a therapeutic alternative for intestinal diseases [162]. Direct delivery of SCFA by encapsulation allows the supplementation without the need for fermentation, increasing the release in the distal gastrointestinal section [163]. Multiple studies have shown that SCFAs are beneficial as a drinking water supplement and feed additive for the

In young chickens, *Salmonella enterica spp. enteritidis* cecal colonization significantly decreased when butyric acid was added to the feed [166, 167]. The

control of Salmonella, Campylobacter and Clostridium [164, 165].

**130**

IL-10 [156, 161].

immune defense and bridge innate and adaptive immune responses at mucosal surfaces. Understanding the complex function and regulation of these immune components may offer new insights into the nutritional prevention and treatment of infectious and inflammatory diseases that originate at mucosal surfaces. Some studies have been addressed the role of key nutrients modulating this secretory defense system and aiding to the host to counteract the noxious effect of harmful microorganism. Based on that, nutrition would be considered as an important strategy in the reduction of antibiotic growth promotants. However, more studies are needed to understand the effects of nutrients on gut immune response against pathogens.
