In this review, the terminology that is used to describe the bioavailability and ileal digestibility of AA in pig feed ingredients is defined. Aspects of the methodology to establish bioavailability and ileal digestibility values also are discussed, and recommendations about the use of these values are provided. Two main factors can contribute to differences between bioavailability and ileal digestibility of AA. First, some AA, such as Lys, may be absorbed in chemical complexes that preclude their use for metabolism. Second, fermentation in the upper gut may result in a net loss or gain of AA to the animal. In addition, dietary effects on the efficiency of using bioavailable AA intake for tissue growth or milk production should be considered and may be attributed to endogenous AA losses in the hindgut and the metabolic costs associated with endogenous gut protein synthesis and losses. Ileal digestibility values may be expressed as apparent ileal digestibility (AID), standardized ileal digestibility (SID), or true ileal digestibility (TID). These terms are used to specify how ileal endogenous AA losses are reflected in digestibility values. Ileal endogenous AA losses may be separated into basal losses, which are not influenced by feed ingredient composition, and specific losses, which are induced by feed ingredient characteristics such as levels and types of fiber and antinutritional factors. Values for AID are established when total ileal outflow of AA (i.e., the sum of endogenous losses and nondigested dietary AA) is related to dietary AA intake. A concern with the use of AID values is that these are not additive in mixtures of feed ingredients. This concern may be overcome by correcting AID values for defined basal endogenous losses of AA, which yields SID values. Furthermore, if the AID values are corrected for basal and specific endogenous losses, then values for TID are calculated. However, reliable procedures to routinely measure specific endogenous losses are not yet available. It is recommended that basal ileal endogenous losses of AA should be measured in digestibility experiments using a defined protein-free diet and that these losses are reported with observed AID and SID values. It is suggested that SID values should be used for feed formulation, at least until more information on TID values becomes available.

This study investigated intestinal physiology of piglets at weaning. Piglets (n = 60) weaned at 21 d were food deprived for 2 d and then tube-fed using 2 different diets (a conventional diet vs. a wheat-enriched diet). They were slaughtered at d 0, 2, 5, 8, or 15 postweaning. Jejunum, ileum, and colon were mounted in Ussing chambers. In addition, segments of the proximal jejunum of 4 growing pigs were studied 35 d after weaning. Secretory function was assessed by basal short-circuit current (Isc) and secretagogue-stimulated Isc. Glucose absorption was measured by the increase in Isc after the addition of glucose. Epithelial barrier function was measured by transmucosal resistance (R) and horseradish peroxidase (HRP) fluxes across the epithelium. There were no significant differences between the pigs fed the 2 diets for any of the parameters studied. As already reported, a transient villous atrophy was observed. At the same time, we observed an increased basal Isc in jejunum and colon, increased glucose absorption and a dramatic drop of R in jejunum. These parameters had returned to preweaning values by d 5. Weaning was also followed by long-lasting modifications. In jejunum, responses to the secretagogues and glucose absorption were decreased at wk 2 after weaning and were not different between d 15 and 35. Ileal transmucosal resistance increased on d 5 and was stable thereafter. HRP flux in jejunum declined on d 2 and stayed at this low level throughout the experiment. We conclude that weaning induces transient dramatic changes in intestinal physiology but is also a period of maturation of the intestine.

-The post-weaning period in pigs is characterized by an immediate but transient drop in feed intake resulting in severe undernutrition and growth check. This in turn affects various aspects of small intestinal architecture and function leading to gut-associated disorders and often diarrhea. Among these, villus atrophy and digestive enzyme activity depression have been documented. More recent investigations clearly demonstrate early signs of local inflammation including immune cell infiltration and increased pro-inflammatory cytokine gene expression, signs of cytoprotection through up-regulation of so-called heat shock proteins, indications of tissue alterations by proteases (stromelysin) and finally epithelial functional disorders in mineral absorption/secretion and permeability. This is followed by a regenerative phase, probably stimulated by feed intake resumption, resulting in down-regulation of many intestinal indicators. However, some of them then display new spatio-temporal adult-type adaptive patterns of maturation. A limited number of substances, particularly nitrogenous compounds and complex preparations of animal origin (colostrum, plasma) have proven to be successful, at least partly, in minimizing post-weaning intestinal disturbances. Thus further research in intestinal physiology, in association with microbiology and immunology, is warranted to strengthen our understanding of the mechanisms of gut disorders in order to provide a better rational basis for designing suitable alternatives to in-feed antibiotics for pigs. clairement montré des signes précoces d'inflammation incluant une infiltration cellulaire et l'expression accrue des gènes de plusieurs cytokines inflammatoires, une cytoprotection renforcée par la sur-expression des protéines du choc thermique, des indications d'altérations tissulaires par des protéases (stromélysines), et finalement des désordres fonctionnels épithéliaux d'absorption et de sécrétion minérales et de la perméabilité intestinale. Ceci est suivi par une phase de régénération intestinale, probablement stimulée par la reprise de consommation alimentaire, et conduisant à un retour à la normale de plusieurs indicateurs. Cependant, certains d'entre eux ont évolué vers des profils spatio-temporels adaptatifs de type adulte. Un nombre limité de substances, particulièrement des composés azotés et des produits animaux (colostrum, plasma) ont démontré leur capacité, au moins partielle, à minimiser les perturbations digestives post-sevrage. De nouvelles recherches en physiologie digestive, en association avec la microbiologie et l'immunologie, sont nécessaires pour renforcer notre compréhension des mécanismes des troubles digestifs. Ceci permettra de fournir des bases plus rationnelles pour développer des solutions alternatives satisfaisantes aux antibiotiques dans les aliments pour porcelets.intestin / nutrition / physiopathologie / porcelet / sevrage

Cytokines play a central role in immune cell response, but they also participate in the maintenance of tissue integrity. Changes in the cytokine network of the pig gut may be expected at weaning, because abrupt changes in dietary and environmental factors lead to important morphological and functional adaptations in the gut. This study measured the gene expression of 6 inflammatory cytokines along the small intestine (SI) and the proximal colon in 28-d-old piglets (n = 45) at different time points (0, 1, 2, 5 and 8 d) postweaning, using RT-PCR. Villus-crypt architecture and enzymatic activities of lactase and sucrase in the SI were also examined. The results confirmed that weaning is associated with morphological and enzymatic changes in the SI. In addition, the data indicated that cytokine response in the gut could be divided into two periods: an early acute response (0 to 2 d postweaning) and a late long-lasting response (2 to 8 d postweaning). Between d 0 and d 2, the levels of IL-1beta, IL-6, and TNF-alpha messenger RNA (mRNA) increased. Marked upregulation of IL-1beta mRNA occurred in most parts of the intestine, whereas IL-6 and TNF-alpha mRNA markedly increased only at specific sites in the intestine. Between d 2 and d 8, the levels of IL-1beta, IL-6, and TNF-alpha mRNA rapidly returned to preweaning values, except that the level of TNF-alpha mRNA remained high in the distal SI. Levels of IL-12 subunit p40 (IL-12p40) and IL-18 mRNA also decreased, compared to those on d 0. Taken together, these results demonstrate that weaning in piglets is associated with an early and transient response in gene expression of inflammatory cytokines in the gut.