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The EU ban on in-feed antibiotics has stimulated research on weaning diets as a way of reducing post-weaning gut disorders and growth check in pigs. Many bioactive components have been investigated but only few have shown to be effective. Amongst these, organic acids (OA) have been shown to exert a bactericidal action mediated by non-dissociated OA, by lowering gastric pH, increasing gut and pancreas enzyme secretion and improving gut wall morphology. It has been postulated that they may also enhance non-specific immune responses and improve disease resistance. In contrast, relatively little attention has been paid to the impact of OA on the stomach but recent data show they can differently affect gastric histology, acid secretion and gastric emptying. Butyrate and precursors of butyric acid have received special attention and although promising results have been obtained, their effects are dependent upon the dose, treatment duration, initial age of piglets, gastrointestinal site and other factors. The amino acids (AA) like glutamine, tryptophan and arginine are supportive in improving digestion, absorption and retention of nutrients by affecting tissue anabolism, stress and (or) immunity. Glutamine, cysteine and threonine are important for maintaining mucin and permeability of intestinal barrier function. Spray-dried plasma (SDP) positively affects gut morphology, inflammation and reduces acquired specific immune responses via specific and a-specific influences of immunoglobulins and other bioactive components. Effects are more pronounced in early-weaned piglets and under poorer health conditions. Little interaction between plasma protein and antibiotics has been found, suggesting distinct modes of action and additive effects. Bovine colostrum may act more or less similarly to SDP. The composition of essential oils is highly variable, depending on environmental and climatic conditions and distillation methods. These oils differ widely in their antimicrobial activity in vitro and some components of weaning diets may decrease their activity. Results in young pigs are highly variable depending upon the product and doses used. These studies suggest that relatively high concentrations of essential oils are needed for beneficial effects to be observed and it has been assumed that these plant extracts mimic most of the effects of antibiotics active on gut physiology, microbiology and immunology. Often, bioactive substances protective to the gut also stimulate feed intake and growth performance. New insights on the effects of selected OA and AA, protein sources (especially SDP, bovine colostrum) and plant extracts with anti-bacterial activities on the gut are reported in this review. [ABSTRACT FROM AUTHOR]

The functional adaptability of the digestive system to the level of feed intake was investigated in the young rabbits by comparing two groups of 12 litters each, weaned at 21 (W21) or 35 (W35) days of age. From 14 days onwards, rabbits were fed a pelleted feed (NDF: 332 g/kg, CP: 177 g/kg, starch: 98 g/kg, as-fed basis). Until 49 days of age, the profile of digestive enzymes was weekly determined in the small intestinal content and mucosa, as well as caecal fermentation traits and fibrolytic activities. In the W21 group, the solid feed intake was increased by 57% between 21 and 35 days (P < 0.01), while the daily body growth was lower from 21 till 42 days (-17%, P < 0.05) when compared with the W35 group. Activities of enzymes of pancreatic origin were only scarcely influenced by the weaning age. In the W21 group, amylase activity tended to be lower at 28 days of age (-36%, P = 0.064), and trypsin activity was decreased by 31% at 49 days of age (P < 0.01). Lipase activity was similar in both weaning groups. Duodenal and jejunal activities of maltase and aminopeptidase N (APN) were higher on day 28 in the W21 group as compared with the W35 group (×1.4 to ×2.4, respectively, P < 0.05). On day 35, duodenal APN activity was twice as higher in the W21 group than in the W35 group (P < 0.01). In caecum, major differences between both weaning groups were observed at 28 days of age with a decrease in ammonia concentration (-43%, P < 0.01) in W21 compared with W35 rabbits. Conversely, the acetate proportion was 5% higher in the W21 group (P < 0.01) on day 28. In conclusion, the digestive tract of early-weaned rabbits showed some adaptative properties in response to nutritional environment changes, but they were insufficient to maintain their growth rate.

The weaning of piglets is often associated with digestive disorders, particularly diarrhea--postweaning colibacillosis (PWC)--which is caused by infection with enterotoxigenic strains of Escherichia coli. It has been shown previously that a diet for newly weaned pigs based on cooked white rice and animal protein decreases the occurrence of PWC, whereas the addition of carboxymethylcellulose (CMC) to this diet enhances PWC. The aims of the current work were to 1) determine whether substitution of animal protein with plant proteins in the cooked-white-rice diet influenced its protective effects on PWC and 2) confirm that an increase in viscosity of the digesta by adding CMC to the diet favors the development of PWC--with (Exp. 1) or without (Exp. 2) experimental infection of piglets with E. coli. The diets were 1) cooked white rice and animal protein sources (RAP), 2) RAP + CMC added at 40 g of CMC/kg (air-dry basis) of diet, 3) cooked white rice and plant protein sources (RPP), and 4) wheat and plant protein sources (WPP). Experiments 1 and 2 were conducted using 32 and 24 piglets (eight and six per treatment), respectively. Piglets were weaned at 21 d (d 1), and fed ad libitum until slaughter on d 9. In Exp. 1, piglets were orally infected with enterotoxigenic E. coli on d 4, 5, 6, and 7. On d 8 of Exp. 1, the E. coli scores in feces of pigs fed RAP + CMC were higher than with RAP (P < 0.01). On d 9 after weaning, feces from pigs fed diet RAP were normal or moist, whereas feces from pigs fed RAP + CMC were wet to diarrheic. On d 7 of Exp. 2, pigs fed diets RAP + CMC and WPP had wetter feces than pigs fed diets RAP or RPP (P < 0.05). On d 8, the E. coli scores in feces were higher (P < 0.01) with pigs fed RAP + CMC than with all other diets. The E. coli scores in the digesta were also higher with pigs fed RAP + CMC, and to a lesser extent with diet WPP, than with pigs fed RAP or RPP (P < 0.01). The large intestine was heavier in pigs fed diets RPP and WPP, and the digesta were more acidic (P < 0.05). This study confirmed that diet RAP was protective against PWC, and that substitution of animal proteins with plant protein in a rice-based diet did not diminish its protective effects. The addition of CMC to cooked white rice increased digesta viscosity and enhanced PWC. Consequently, this diet represents a useful model for studying this condition.

The mucus gel covering the gut epithelium is in dynamic balance between synthesis and secretion of mucin from goblet cells and proteolytic and physical erosion that releases mucin into the lumen. In the lumen, mucin is partially protected from proteolysis by carbohydrate chains, and it contributes to endogenous protein reaching the ileum. Dietary components modulate the contribution of mucin to endogenous protein components and their qualitative composition. In addition, mucin plays a key role in gastrointestinal protection in association with the microflora. In this review, we will attempt to evaluate the consequences of dietary manipulation of mucin on gut health.

The objective of this study was to examine the effect of the dietary crude protein (CP) content and source on the distribution of digesta proteins and peptides according to their molecular mass along the small intestine of veal calves. Diets contained 14, 104, 205, and 279 g/kg of CP supplied by skim milk powder (SMP) in experiment 1. Diets contained only SMP or SMP plus proteins (1:1 on digestible CP basis) from either a soybean protein concentrate (SPC), an isolated soy protein partially hydrolyzed (HSPI), or a potato protein concentrate (PPC) in experiment 2. Duodenal, jejunal, and ileal digesta were collected from calves fitted with simple cannulae and continuously infused the milk replacers into the abomasum. The distribution of molecular mass (Mr) of proteins and peptides was studied by gel filtration chromatography. Increasing the dietary CP level of milk replacers increased the flow of oligopeptides and free amino acids in ileal digesta. Incorporating plant protein increased the flow of proteins with Mr > 20,000 in the duodenum and that of proteins and peptides with Mr < 10,000 in the ileum. Hydrolysis of oligopeptides and absorption may be a limiting step in the digestion of plant protein in the veal calf.

This study was performed with growing chickens (4 to 22 d of age) to evaluate the effects of feeding a rye-based diet supplemented with commercial enzyme preparation containing xylanase and beta-glucanase (Quatrazyme HP, Nutri-Tomen, France) on small intestine wall morphology, bile acid composition, nutrient digestibility, and bird performance compared with unsupplemented rye- or corn-based diets. The rye-based diet decreased (P < or = 0.05) weight gain, feed intake, and feed efficiency and increased water intake compared with the corn-based diet. Moreover, rye consumption reduced crude fat and protein digestibility as well as apparent metabolizable energy (P < or = 0.05). The small intestine wall showed that villus length, width, and surface were decreased in broiler chickens fed the rye-based diet compared with those fed the corn-based diet. However, crypt morphometry parameters were not affected by diet type. The concentration of conjugated bile acids in the small intestine contents of broiler chickens fed the rye-based diet was decreased (P < or = 0.05) compared with those fed the corn-based diet. These findings suggest that feeding a rye-based diet reduces villus capacity for nutrient absorption and bile acid capacity for fat solubilization and emulsification, resulting in decreased bird performance. The addition of xylanase and beta-glucanase to the rye-based diet improved (P < or = 0.05) weight gain, feed intake, and feed efficiency, and decreased water intake. The digestibility of nutrients and apparent metabolizable energy were also increased (P < or = 0.05). Addition of xylanase and beta-glucanase increased (P < or = 0.05) villus size and the villus height-to-crypt depth ratio, as well as the concentration of conjugated bile acids (P < or = 0.05) in the small intestine contents. Exogenous enzymes improved nutrient digestibility and broiler chicken performance, probably by improving the absorption capacity ofthe small intestine through increased villus surface and intestinal concentration of conjugated bile acids.

The objective of this study was to investigate the effect of the dietary crude protein (CP) content and origin on the flow of mucin protein along the small intestine of the preruminant calf. Diets contained 1, 10, 20 and 28% of CP supplied by skim milk powder (SMP) in experiment 1. Diets differed by the nature of protein [soybean protein concentrate (SPC), partially hydrolyzed soybean protein isolate (HSPI) or potato protein concentrate (PPC)] in experiment 2. Duodenal, jejunal, and ileal digesta were collected from calves fitted with simple cannulae and continuously infused the milk replacers into the abomasum. In experiment 1, the basal flow of mucin protein was 1.1, 1.8, and 4.0 g/kg of dry matter intake at the duodenum, jejunum, and ileum, respectively. Mucin protein contributed to 19 and 40% of ileal loss of CP and lysine, respectively. When dietary CP rose from 1 to 28%, the flow of mucin protein increased at the duodenum (+300%). In experiment 2, the flow of mucin protein increased by 70% at the duodenum and at the jejunum when SMP was partially replaced by SPC and HSPI. With PPC, this flow increased at the duodenum (+24%) and ileum (+52%). These data demonstrate the importance of mucin as a source of endogenous nitrogen and the impact of dietary protein content and origin on this flow.

The aim of this study was to develop a specific ELISA for calf intestinal mucin to quantify its contribution to ileal endogenous losses. Mucin was isolated from intestinal scrapings by cesium chloride density gradient ultracentrifugation. The isolated mucin had a high concentration of glutamic and aspartic acids, threonine, and serine (13.2, 11.2, 9.6, and 9.2 mol % of total amino acids assayed, respectively). The carbohydrates present were (mol % of total hexoses): galactose 42.1, N-acetylglucosamine 24.1, N-acetylgalactosamine 23.6, fucose 4.7, mannose 3.1, and sialic acids 2.4. Amino acids and carbohydrates represented 52.6 and 47.4% of the mucin by weight, respectively. A rabbit hyperimmune plasma was raised against purified mucin and used to set up an ELISA. The linear range of this assay was 20 to 640 ng/ml. The plasma cross-reacted with calf abomasal and colonic mucin. It showed no cross-reactivity with nonmucin components and no reactivity with intestinal mucin from other animal species except for the rat. Mucin accounted for approximately 3.5% of the dry matter output at the ileum of calves fed a substitute milk based on skim milk powder. This represented a flow of 3.4 g of mucin/kg of dry matter intake. Mucin flow increased when dietary protein was provided by cow's colostrum. Finally, the developed assay is a suitable tool to investigate the impact of dietary factors on the flow of mucin along the gut of preruminant calves.

A study was undertaken to assess the impact of the protein nature and soya antigenicity on the morphology and some enzyme activities of the jejunum in preruminant calves. Twenty Holstein calves fitted with a duodenal cannula were fed a liquid diet based on skimmed milk powder (SMP) for 2 weeks. They were then switched onto diets containing a mixture of SMP and either antigenic heated soybean flour (HSF; n = 12) or hypo-antigenic soya protein concentrate (SPC; n = 8) for 8 weeks, after which they were reverted back to the SMP diet for 2 weeks. The diets contained similar amounts of digestible nitrogen and energy, and were fed at a rate of 55 g DM/kg(0.75)/d. Proximal jejunal biopsies were collected just before (week 0), during (weeks 2 and 8) and after (week 10) feeding of the soya-based diets, and were used for morphology measurements and the determination of total alkaline phosphatase, lactase, amino-peptidases A and N, and dipeptidyl peptidase IV activities. Feed intake and growth were similar between the HSF and SPC groups during the experimental period. The effects of antigenicity and the antigenicity x time interaction were never significant (P > 0.05). Villus height decreased (P < 0.01) between weeks 0 and 2, and increased (P < 0.05) between weeks 8 and 10. Villus width increased between weeks 2 and 8 (P < 0.001). Crypt depth also increased between weeks 0 and 2 (P < 0.001). Specific activities of alkaline phosphatase (P < 0.01) and amino-peptidase N (P < 0.05) decreased between weeks 0 and 2. Conversely, those of alkaline phosphatase (P < 0.0001), lactase (P < 0.01) and dipeptidyl-peptidase IV (P < 0.0001) increased between weeks 8 and 10. Specific activities for lactase and amino-peptidase N decreased (P < 0.01) between weeks 2 and 8. The treatments had little effects on the amino-peptidase A activity. In conclusion, the present work demonstrated that soybean protein markedly depressed the morphology and most enzyme activities of the calf small intestine. On the contrary, the in vitro antigenicity of soybean protein had little influence on these parameters in this study.

Two experiments were conducted to study gastric and small intestinal digestion of soybean glycinin and beta-conglycinin in preruminant calves fed milk replacers containing a mixture of skim milk powder and antigenic heated soybean flour. In experiment 1, duodenal passage of immunoreactive beta-conglycinin lasted for a much longer time after the morning meal than that of glycinin. Western blotting revealed the early abomasal outflow of glycinin subunits that associated nearly intact basic polypeptides to partially degraded acidic polypeptides. Intact beta-conglycinin was evidenced at most sampling times. In experiment 2, intact basic glycinin (M(r) = 21000) associated with partially digested acidic glycinin (7000 < M(r) < 25000) was demonstrated in ileal digesta up to 8-10 h after the meal. beta-Conglycinin immunoreactivity could not be evidenced by Western blotting in ileal digesta.

Increasing the roasting time of soybeans from 15 (RSF15) to 25 (RSF25) min led to an important decrease in the antitryptic activity and immunoreactivity of the storage globulins, but it did not seem to greatly affect the concentrations of the indispensable amino acids in the protein. The RSF15 and RSF25 flours were used as the only protein sources in balanced diets for growing rats, and they were compared to a diet based on casein in a pair-feeding experiment. When roasted as usually happens at the workshop level (RSF15), soybean flour induced a significant hypertrophy of the pancreas. Increasing the roasting time by up to 25 min considerably improved the nutritional value of the soybean protein, without apparent consequence on the levels of free amino acid pools in the plasma and muscles. The data also indicated that the tissues of the small and large intestines of the young rat were sensitive to the hyperactivity of the intestinal microflora, and also possibly to the residual activity of some antinutritional factors.

Intestinal motility disorders and some mediators implicated in these disorders were studied in preruminant calves that had been chronically fed a diet containing an antigenic heated soyabean flour (HSF) for 3 months. The calves in the present study had previously been shown to present strong immune reactions against soyabean proteins, as assessed through plasma antibody titres, direct skin tests and in vitro lymphoproliferation. Four of these calves sensitive to soya were fitted with an abomasal catheter and wire electrodes on the jejunum. Myoelectric activity was recorded over 7 h following test meals containing skim milk powder (SMP), HSF or a non-antigenic hydrolysed soya protein isolate (HSPI). The pattern of myoelectric complexes migrating to the jejunum was regular with SMP (mean durations of phases I, II and III: 26, 38 and 5.28 min, respectively). With HSF, diarrhoea appeared, and the total duration of phase I decreased from 149 to 68 min (P < 0.01) while that of phase II increased from 239 to 328 min (P < 0.01). The mean duration of phase III decreased from 5.3 to 3.9 min (P < 0.01). These changes, including diarrhoea, were substantially reversed by feeding HSPI. When promethazine, a H-1 histamine receptor antagonist, was administered i.v. prior to feeding HSF the number of phases I tended to decrease and diarrhoea virtually disappeared. In contrast, indomethacin, a cyclooxygenase inhibitor, had limited effects on motility patterns and diarrhoea. These disorders were partially reproduced by i.p. administration of platelet-activating factor (PAF) prior to feeding with SMP. These findings suggest that calves chronically fed antigenic soya suffer from immune-mediated motility disorders which are linked to histamine action via H-1 receptors, and possibly with PAF. The role of arachidonic acid catabolites of the cyclooxygenase pathway is probably minor.

The effect of dietary antigens on the gut morphology and density of immune cells was studied in preruminant calves fed milk substitutes containing skim milk powder (SMP), non-antigenic hydrolysed soya protein isolate (HSPI) or antigenic heated soyabean flour (HSF) as their main protein source for 3 months. The height and perimeter of proximal jejunum villi were highest in the calves fed SMP and lowest in those fed HSF (P < 0.05). In contrast, the crypt depth and perimeter were apparently not influenced by the dietary treatments studied. This morphological alteration was associated with a dramatic infiltration of the lamina propria by B and T lymphocytes in the calves fed HSF (P < 0.01). Increased B cell density was essentially accounted for by IgA-, IgG1- and IgG2-bearing cells. The density of CD2-positive T lymphocytes increased (P < 0.01) in the jejunal lamina propria of HSF calves, involving helper (CD4+) and suppressor-cytotoxic (CD8+) T cell subsets. The density of gamma-delta (WC1+) T cells also increased (P < 0.01). The major change concomitantly observed in the villus epithelium was an increased density of CD8+ cells (P < 0.05) and WC1 + cells (P < 0.01).