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The impact of dietary fiber on fecal digestion is well-known and provides a comprehensive approach toward nutrient digestibility and availability. Little quantitative information is available on digestion of fiber in the different segments of the gastrointestinal tract (GIT). The objectives of this study were to obtain a method allowing the quantification of the digestive process in different segments of the GIT and to study the impact of dietary fiber on nutrient digestibility. Six barrows (average initial BW of 30 kg and fitted with a simple T-cannula at the proximal duodenum and caudal ileum) were used in a replicated 3 x 3 Latin square design. In each period, pigs were offered 1 of 3 diets differing in fiber content (low, medium, and high). Differences in fiber content were created by replacing wheat and barley with wheat bran. Titanium dioxide was included in the diet as an indigestible marker to determine the apparent digestibility coefficients in different segments of the GIT. The apparent digestibility of ash, CP, DM, and OM increased in the different segments of the GIT. Duodenal digestibility coefficients were negative for ash (e.g., -39.9% for the mediumand high-fiber diets), indicating important endogenous mineral secretions by the stomach and digestive glands. The duodenal digestibility of other nutrients and OM were positive but close to zero and numerically lower in the diets with the greater fiber contents. The fiber content in the diet did not affect the apparent ileal digestibility of nutrients. Increasing the fiber content in the diet affected the fecal digestibility of CP, ether extract, and energy (P < 0.01). The method used for studying sites of digestion in the digestive tract provides promising results, but it is limited due to the high variability that is likely caused by sampling limitations and variation between animals. Key words: dietary fiber, digestion, endogenous secretion, pig

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 red 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 red RAP + CMC than with all other diets. The E. coli scores in the digesta were also higher with pigs red 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 red 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. Key Words: Diarrhea, Enterotoxigenic E. coli, Postweaning Colibacillosis, Rice, Weaning Piglet

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. Key words: mucus, mucin, endogenous losses, digestion, protein