Weaning stress and gastrointestinal barrier development: Implications for lifelong gut health in pigs

Colostrum intake from birth to 24 h after the onset of parturition (T24) was estimated for 526 piglets from 40 litters. Plasma concentrations of immunoglobulin G (IgG), lactate, glucose and cortisol were determined at T24 for six piglets per litter. Plasma IgG concentration was also assayed at weaning (28 days) on the same piglets. Rectal temperature was measured at T24 on all piglets. Mortality was recorded until weaning and comparisons were made between piglets that died before weaning and those that were still alive at weaning. The piglets that died before weaning had lower birth weight, lower colostrum intake, lower weight gain between birth and T24, and had a lower rectal temperature, higher plasma cortisol concentration and lower plasma IgG and glucose concentrations at T24 than piglets still alive at weaning. In addition, a higher proportion of piglets that died before weaning had difficulty taking their first breath after birth and were affected by splayleg. Considering all piglets, colostrum intake was positively related to rectal temperature and plasma glucose concentration and negatively related to plasma cortisol concentration at T24. Plasma IgG concentration at T24 was explained by colostrum intake, IgG concentration in the ingested colostrum, birth weight and birth rank (P<0.0001). Plasma IgG concentration at weaning was related to plasma IgG concentration at T24 (r=0.54; P<0.0001) and to colostrum intake (r=0.32; P<0.0001). Finally, body weight was explained by colostrum intake, birth weight and age until 6 weeks of age (P<0.0001). These results show that colostrum intake is the main determinant of piglet survival through provision of energy and immune protection and has potential long-term effects on piglet growth and immunity.

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Influence of colostrum intake on piglet survival and immunity.

This article reviews thyroid function and its hypothalamic-pituitary-thyroid (HPT) axis control in birds with emphasis on the similarities and differences in thyroid function compared to mammals and other vertebrate classes. Thyroid hormones are important in metabolism and the thermogenesis required for homeothermy in birds, as in mammals, the other homeothermic class of vertebrates. Thyroid hormones play important roles in development and growth in birds, as is the case for all vertebrate classes. The developmental effects of thyroid hormones in birds are presented in the context of differences in precocial and altricial patterns of development and growth with emphasis on oviparous development. The sections on thyroid hormone actions include discussion of effects on the development of a number of tissue types as well as on seasonal organismal processes and interactions of the thyroid axis with reproduction. The current picture of how environmental chemicals may disrupt avian thyroid function is relatively limited and is presented in the context of the assessment endpoints that have been used to date. These endpoints are categorized as thyroid and HPT axis endpoints versus target organ endpoints. The final section discusses two recommended assay protocols, the avian two-generation toxicity assay and the avian one-generation assay, and whether these protocols can evaluate thyroid disruption in birds.

The hypothalamic-pituitary-thyroid (HPT) axis in birds and its role in bird development and reproduction.

Uptake of colostrum just after birth is essential to stimulate intestinal growth and function, and in many species, including pigs, colostrum also provides immunological protection via the absorption of immunoglobulin G (IgG). In this study, intestinal growth, IgG absorptive capacity and enzyme activities were investigated in newborn pigs in response to different diets. Newborn piglets were bottle-fed porcine colostrum (PC), bovine colostrum (BC), porcine plasma (PP), porcine milk (PM), bovine colostrum containing porcine plasma (BCP) or a milk replacer (MR) every 3 h (15 mL/kg) for up to 2 d. Bovine serum albumin (BSA) was added to the diets as a macromolecule marker. The percentage of absorbed BSA just after birth was highest for piglets fed the PC diet (30-50%), lower for those fed the BC and BCP diets (23-30%) and lowest for the PP, PM and MR diet-fed piglets (7-20%, P < 0.05 relative to those fed colostrum). Porcine IgG was absorbed more efficiently than bovine IgG. Intestinal closure occurred earlier in MR and BCP piglets (within 12 h after birth) than in PC pigs. At 2 d of age, intestinal mucosal weight (+120% increase from birth) and villus morphology were similar in the PC, BCP and MR groups. All 3 groups also had increased aminopeptidase A activity compared with values at birth (+100% increase). Compared with PC pigs, the BCP group had higher sucrase and maltase activities (+50% and +200%, respectively) and lower aminopeptidase N activity (-50%, P < 0.05). Similarly, MR pigs showed elevated sucrase activity (+40%) and lowered maltase, lactase and aminopeptidase N activities (-20% to -50%, P < 0.05) compared with PC pigs. We conclude that porcine and bovine colostrum contain factors that stimulate the intestinal endocytotic and enzymatic capacity in newborn pigs. A milk replacer can produce normal gut growth, but may be inefficient in mediating normal macromolecule transport and disaccharidase activity. Bovine colostrum mixed with porcine plasma proteins may be a useful substitute for porcine colostrum in artificial rearing of newborn pigs.

Development of Intestinal Immunoglobulin Absorption and Enzyme Activities in Neonatal Pigs Is Diet Dependent

Neonatal mortality is very high in farm animals (approximately 10%) and disease resistance is greatly influenced by an adequate passive immunisation just after birth. In piglets, foals, calves and lambs, the intestinal absorption of immunoglobulins from their mother's colostrum occurs mainly by a non-specific endocytosis of macromolecules, but the details of the absorption process, and the mechanisms regulating its cessation after 1-2 days of colostrum exposure, remain poorly understood. In both normal and 'compromised' (premature, growth-retarded, hypoxic, lethargic) newborn farm animals, the intestinal capacity to absorb macromolecules is influenced by both diet- and animal-related factors. Thus, macromolecule uptake is severely reduced in response to premature birth and when macromolecules are to be absorbed from diets other than species-specific colostrum. On the other hand, fetal growth retardation, in vitro embryo production, or a stressful birth process are unlikely to reduce the ability of the intestine to absorb immunoglobulins from colostrum. More knowledge about the diet- and animal-related factors affecting intestinal immunoglobulin uptake will improve the clinical care of 'compromised' newborn farm animals. The present text gives a brief introduction to the process of intestinal immunoglobulin absorption in large farm animals and describe some recent results from the author's own studies in pigs, calves and lambs.

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Uptake of colostral immunoglobulins by the compromised newborn farm animal

Changes in the IgG concentration in the colostrum from separate teats of 6 sows and those in the sera of their 38 piglets were investigated. Colostrum was frequently sampled from parturition to 120 hours and blood was taken from the piglets from birth to 10 weeks of age. The IgG content of the colostrum decreased to 3.2% of the original concentration at the 5th day of lactation. The meaningful variation of the IgG concentration of the colostra obtained from different teats increased rapidly from 12 hours postpartum. Between-sow variation was high and no correlation of the IgG concentration of the colostrum with the average serum level of the corresponding litter could be confirmed. Of the newborn pigs, 33% possessed IgG before ingesting colostrum, the observed concentration was 0.09±0.02 mg/ml (mean±SEM). At 0.5 and 1.5 hours after access to colostrum, this value was 2.30±1.38 and 1.89±0.60 mg/ml respectively. The highest IgG concentration (39.45±1.46) was observed at 24 hours after birth. Following that, a stepwise drop occurred in the IgG level and the lowest value was observed in the 4th week of age (8.92±0.59 mg/ml). Subsequently, there was a continuous rise until 10 weeks of age when the concentration reached the value characteristic of adults. The calculated half-life of the IgG in the sera showed a significant between-litter variation. The average half-life of the serum IgG of pigs was 9.73 days.

Changes in colostral and serum IgG content in swine in relation to time.

The hypothyroid chicken brain has been found to preserve more triiodothyronine (T3) than expected from plasma T3 levels. A possible explanation is that the elimination of T3 from the hypothyroid brain is decreased. In the present experiments, the elimination rate of T3 was compared in surgically thyroidectomized animals and sham-operated controls. It was found that both T3 coming from the plasma and T3 derived locally in the cells from thyroxine have a significantly lower elimination rate in thyroidectomized chickens than in sham-operated ones. Therefore it is concluded that the adaptation of the brain to hypothyroid conditions is partly regulated by reducing the loss of the active thyroid hormone (i.e. T3) via metabolic and tissue-to-plasma exchange.

Elimination and metabolism of triiodothyronine depend on the thyroid status in the brain of young chickens.

The interaction of homologous and heterologous IgG during intestinal absorption was investigated using five groups of newborn piglets (50 animals in total). The diet, given via a stomach tube, was different in each group during the first 24 h. Group I received bovine colostrum, group II bovine colostrum and porcine IgG solution, group III bovine and porcine colostrum, group IV bovine colostrum and intraperitoneally applied monomeric porcine IgG, and group V received a glucose diet with no immunoglobulins. Feeding was based on bovine colostrum between the 2nd and 6th days after birth, followed by a milk replacer during the rest of the experimental period. The serum concentrations of homologous and heterologous IgG were monitored from birth to 10 weeks of age. The total serum IgG content (homologous + heterologous) of newborns was almost equal in groups I-IV at 24 h. Porcine IgG from endogenous synthesis was detectable in the serum of groups I and V two weeks postpartum. The heterologous IgG absorbed from bovine colostrum produced nearly the same serum concentration in groups II and III: hence the different components of porcine colostrum did not influence the absorption of heterologous IgG. Intraperitoneal application of 1.3 g porcine IgG in group IV resulted in a delay of the synthesis of endogenous IgG. The average half-life of heterologous IgG in the serum of groups I-IV was almost exactly the same, showing that the porcine colostrum or IgG solution did not modify the half-life of bovine IgG.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the absorption of homologous and heterologous IgG in artificially reared newborn pigs

Thyroid dysfunction causes certain dermatological alterations in dogs. Insufficient delivery of thyroid hormone to the skin may originate not only from inadequate thyroid function but also from impaired local activation of thyroxine in the target organ. Thyroid parameters and deiodination were investigated in healthy dogs (group C) and in dogs with cutaneous lesions associated with hypothyroidism (group H) or with a low-T3 syndrome (group LT). The ability of the skin to convert T4 to T3 was impaired in both groups H and LT but not in the controls. It is concluded that impaired local deiodination may contribute to skin problems in dogs.

V. L. Frenyo

Papers

Changes in colostral and serum IgG content in swine in relation to time.

Elimination and metabolism of triiodothyronine depend on the thyroid status in the brain of young chickens.

Studies on the absorption of homologous and heterologous IgG in artificially reared newborn pigs

Impaired local deiodination of thyroxine to triiodothyronine in dogs with symmetrical truncal alopecia.