**3. Challenges with transfer of immunity to piglets**

The neonate piglets are born without the protection of immunoglobulins because of the epitheliochorial nature of the porcine placenta, which does not allow transfer of large molecules during the maternal-fetal interface. Neonate piglets must acquire maternal immunoglobulins from ingested colostrum for passive immune protection, before they will adequately produce own immunoglobulins at 3–4 weeks of age [32].

In Europe in the last 30 years there has been a constant increase in number of piglets born, with litter size averagely increasing from 11 to 14 piglets, with some countries reaching an average of 16 piglets [33, 34]. Nowadays, having litters up to 18–20 piglets it is not uncommon when raising hyper-prolific sow lines [18, 34, 35]. Because sows can have averagely an udder with 14–16 teats [36], large litters are challenging to manage during lactation. According to Andersen et al. [37], without balancing of litter size after birth and without any direct help to sow and piglets, a sow is able to wean successfully no more than 10 to 11 piglets. Large litters can also directly affect piglets at birth. The larger is the number of piglets born in a litter, the lower is their average birthweight and the higher is their weight variation within the litter [38–41]. A greater number of piglets born than the available teats at the sow's udder, a lower birthweight and a greater birthweight variation, all increase the piglets' competition for colostrum intake [42]. Similarly, lower birthweight and long farrowing duration are associated with lower piglet vitality at birth, which can delay the access to the udder [43, 44].

The constant presence of maternally secretory IgA (sIgA) in milk guarantees the protection of the intestinal mucosa of piglets. As long as piglets are able to intake sufficient amounts of milk, the sIgA give a localized protection to their intestine, allowing them to develop gradually their own immune response mechanisms [45]. Other immunoglobulins, like IgG are more concentrated into colostrum, with most of colostrum produced before farrowing and right after farrowing [46]. Porcine colostrum contains very high levels of IgG (30-70 g/l) and a mixture of bioactive molecules like growth factors and enzymes. In colostrum, the level of IgG may be four times higher than the level of IgA and IgG in the serum of the sow [2]. Closure of the gut junctions in piglets occurs 24–36 h after their birth, making the absorption of immunoglobulins impossible [32]. Impossibility for piglets to obtain timely a sufficient intake of colostrum is considered the main cause of piglet deaths occurring within the first days after birth [47]. The recommended amount of colostrum needed per piglet is at least 200 g to minimize the mortality and 250 g for good body weight gain [47]. Since the amount of colostrum offered is timely limited by the sow own production, there is a possibility that in large litters some of the piglets may suffer lack of colostrum. Lessard et al. [48] suggested that the genes' expression of immunity and oxidative stress in piglets' intestinal tissue can be affected by birth weight and colostrum intake, with direct effects on the leukocyte populations responsible of innate and cell-mediated immunity of nursing piglets. Piglets born with low weight had a lower amount of intestinal antigen presenting cells and an impaired increase of B cells, when compared to high birth weight piglets [48].

Social stress conditions like competition for colostrum and milk intake, crowding, and regrouping are more common in large litters. These conditions may induce short- and long-term effects in pigs, on their immunity. Psychosocial stress may alterate changes in the reactions of both the innate and adaptive immunity, such as leukocyte distribution, cytokine secretion, lymphocyte proliferation, antibody production and immune responses to viral infection or vaccination [49]. In addition, social stress may induce or promote gastrointestinal (GI) diseases through dysregulation of inflammatory processes and glucocorticoid resistance of lymphocytes [49], cortisol being the main stress-induced glucocorticoid in pigs.

**63**

**Figure 2.**

*Netherlands, 2017).*

*Troubled Process of Parturition of the Domestic Pig DOI: http://dx.doi.org/10.5772/intechopen.94547*

and lower birth weight commonly seen in large litter size [2].

Some studies found an increased association between high pre-weaning mortality and large litters [50, 51], one example is given in **Figure 2** for the Netherlands. An explanation to this correlation can be found in prolonged farrowing duration

In a recent study performed in Norway they found that, on the first day of life, the level of piglet plasma IgG, was affected negatively by a linear decrease of 0.4 g/L for each piglet born, indicating how prolonged parturition in large litters can impair the uptake of passive immunity of neonate piglets [52]. Several studies report a negative correlation between litter size and piglet birth weight [38–40, 53]. When looking to piglets' individual growth, three different studies consistently found a decline in litter average birth weight, ranging from 35 to 43 g for each additional pig born across three different populations of litters recorded [39, 40, 54]. A lower birth weight can affect negatively colostrum intake, increasing the risk of mortality [55–57]. Piglets serum IgG concentrations increased with increased piglet weight, while piglets from larger litters had lower serum IgG [58]. Similarly, greater amount of colostrum ingested at birth increased the IgG content in serum of piglets at 24 h after birth [59]. Another study found that piglet serum IgG concentration at 24 h, 10 and 20 days of age was positively correlated with colostrum intake and with the serum IgG concentration of the mother, but was not correlated with birth weight [56]. Increased duration of farrowing in combination with larger competition in the litter, can reduce not only the possibility to intake adequate amount of colostrum, but also retard the time of access to the udder. This is an unfavorable condition considering that colostrum level of immunoglobulins declines fast after the start of parturition [57]. Studies report that a delayed intake, after the birth, of a standard colostrum ration affected negatively the piglets' immunoglobulin absorption and the maturation of their intestinal villi, having possibly long-term harm on their digestion process [60]. A retarded detection of IgG in piglets' serum was reported when the standardized colostrum portion was given only after 12 h from their birth, than in piglets getting it immediately after the birth. The latter piglets had 4.4%

*Increased mortality with increased litter size in the Netherlands (adapted from: AgroVision B.V. the* 

*Troubled Process of Parturition of the Domestic Pig DOI: http://dx.doi.org/10.5772/intechopen.94547*

*Animal Reproduction in Veterinary Medicine*

3–4 weeks of age [32].

**3. Challenges with transfer of immunity to piglets**

The neonate piglets are born without the protection of immunoglobulins because of the epitheliochorial nature of the porcine placenta, which does not allow transfer of large molecules during the maternal-fetal interface. Neonate piglets must acquire maternal immunoglobulins from ingested colostrum for passive immune protection, before they will adequately produce own immunoglobulins at

In Europe in the last 30 years there has been a constant increase in number of piglets born, with litter size averagely increasing from 11 to 14 piglets, with some countries reaching an average of 16 piglets [33, 34]. Nowadays, having litters up to 18–20 piglets it is not uncommon when raising hyper-prolific sow lines [18, 34, 35]. Because sows can have averagely an udder with 14–16 teats [36], large litters are challenging to manage during lactation. According to Andersen et al. [37], without balancing of litter size after birth and without any direct help to sow and piglets, a sow is able to wean successfully no more than 10 to 11 piglets. Large litters can also directly affect piglets at birth. The larger is the number of piglets born in a litter, the lower is their average birthweight and the higher is their weight variation within the litter [38–41]. A greater number of piglets born than the available teats at the sow's udder, a lower birthweight and a greater birthweight variation, all increase the piglets' competition for colostrum intake [42]. Similarly, lower birthweight and long farrowing duration are associated with lower piglet vitality at birth, which can delay the access to the udder [43, 44].

The constant presence of maternally secretory IgA (sIgA) in milk guarantees the protection of the intestinal mucosa of piglets. As long as piglets are able to intake sufficient amounts of milk, the sIgA give a localized protection to their intestine, allowing them to develop gradually their own immune response mechanisms [45]. Other immunoglobulins, like IgG are more concentrated into colostrum, with most of colostrum produced before farrowing and right after farrowing [46]. Porcine colostrum contains very high levels of IgG (30-70 g/l) and a mixture of bioactive molecules like growth factors and enzymes. In colostrum, the level of IgG may be four times higher than the level of IgA and IgG in the serum of the sow [2]. Closure of the gut junctions in piglets occurs 24–36 h after their birth, making the absorption of immunoglobulins impossible [32]. Impossibility for piglets to obtain timely a sufficient intake of colostrum is considered the main cause of piglet deaths occurring within the first days after birth [47]. The recommended amount of colostrum needed per piglet is at least 200 g to minimize the mortality and 250 g for good body weight gain [47]. Since the amount of colostrum offered is timely limited by the sow own production, there is a possibility that in large litters some of the piglets may suffer lack of colostrum. Lessard et al. [48] suggested that the genes' expression of immunity and oxidative stress in piglets' intestinal tissue can be affected by birth weight and colostrum intake, with direct effects on the leukocyte populations responsible of innate and cell-mediated immunity of nursing piglets. Piglets born with low weight had a lower amount of intestinal antigen presenting cells and an impaired increase of B cells, when compared to high birth weight piglets [48].

Social stress conditions like competition for colostrum and milk intake, crowding, and regrouping are more common in large litters. These conditions may induce short- and long-term effects in pigs, on their immunity. Psychosocial stress may alterate changes in the reactions of both the innate and adaptive immunity, such as leukocyte distribution, cytokine secretion, lymphocyte proliferation, antibody production and immune responses to viral infection or vaccination [49]. In addition, social stress may induce or promote gastrointestinal (GI) diseases through dysregulation of inflammatory processes and glucocorticoid resistance of lympho-

cytes [49], cortisol being the main stress-induced glucocorticoid in pigs.

**62**

Some studies found an increased association between high pre-weaning mortality and large litters [50, 51], one example is given in **Figure 2** for the Netherlands. An explanation to this correlation can be found in prolonged farrowing duration and lower birth weight commonly seen in large litter size [2].

In a recent study performed in Norway they found that, on the first day of life, the level of piglet plasma IgG, was affected negatively by a linear decrease of 0.4 g/L for each piglet born, indicating how prolonged parturition in large litters can impair the uptake of passive immunity of neonate piglets [52]. Several studies report a negative correlation between litter size and piglet birth weight [38–40, 53]. When looking to piglets' individual growth, three different studies consistently found a decline in litter average birth weight, ranging from 35 to 43 g for each additional pig born across three different populations of litters recorded [39, 40, 54]. A lower birth weight can affect negatively colostrum intake, increasing the risk of mortality [55–57]. Piglets serum IgG concentrations increased with increased piglet weight, while piglets from larger litters had lower serum IgG [58]. Similarly, greater amount of colostrum ingested at birth increased the IgG content in serum of piglets at 24 h after birth [59]. Another study found that piglet serum IgG concentration at 24 h, 10 and 20 days of age was positively correlated with colostrum intake and with the serum IgG concentration of the mother, but was not correlated with birth weight [56]. Increased duration of farrowing in combination with larger competition in the litter, can reduce not only the possibility to intake adequate amount of colostrum, but also retard the time of access to the udder. This is an unfavorable condition considering that colostrum level of immunoglobulins declines fast after the start of parturition [57]. Studies report that a delayed intake, after the birth, of a standard colostrum ration affected negatively the piglets' immunoglobulin absorption and the maturation of their intestinal villi, having possibly long-term harm on their digestion process [60]. A retarded detection of IgG in piglets' serum was reported when the standardized colostrum portion was given only after 12 h from their birth, than in piglets getting it immediately after the birth. The latter piglets had 4.4%

**Figure 2.** *Increased mortality with increased litter size in the Netherlands (adapted from: AgroVision B.V. the Netherlands, 2017).*

more plasma IgG (21.5 vs. 17.1%), probably because of their greater development of intestinal villi [60]. Klobasa et al. [61] found that birth order had an influence on the amount of immunoglobulin absorbed in a population of 600 piglets. The latest piglets born in the litters had the lower IgG level in their plasma, due to the fast decline in colostrum immunoglobulins level from the start of parturition. Correspondingly, another study reported a 4% decrease of plasma IgG concentration in piglets of smaller birth weight, when compared to their bigger siblings [62]. Manjarin et al. [63] indicated the farrowing-to-suckling interval to be fundamental in the acquisition of adequate IgG by piglets. A 4 h delayed intake of colostrum, after the start of parturition, significantly reduced the amount of piglets' plasma proteins 24 hours up to 12 days. It is therefore extremely important to consider also the time of birth of piglets in relation to the start of farrowing, when planning successful strategies to boost colostrum intake in large litters, like for instance split suckling [2].
