Ileal and hindgut fermentation in the growing pig fed a human-type diet

Dietary fibre fermentation in humans and monogastric animals is considered to occur in the hindgut, but it may also occur in the lower small intestine. This study aimed to compare ileal and hindgut fermentation in the growing pig fed a human-type diet using a combined in vivo/in vitro methodology. Five pigs (23±1.6 kg (mean±SD) bodyweight) were fed a human-type diet. On day fifteen, pigs were euthanised. Digesta from terminal jejunum and the terminal ileum were collected as substrates for fermentation. Ileal and caecal digesta were collected for preparing microbial inocula. Terminal jejunal digesta were fermented in vitro with an ileal digesta inoculum for 2 hours, whereas terminal ileal digesta were fermented in vitro with a pooled caecal digesta inoculum for 24 hours. The ileal organic matter fermentability (28%) was not different from hindgut fermentation (35%). However, the organic matter fermented was 66% greater for ileal fermentation than hindgut fermentation (P=0.04). Total numbers of bacteria in ileal and caecal digesta did not differ (P=0.09). Differences (P<0.05) were observed in the taxonomic composition. For instance, ileal digesta contained 32-fold greater number of the genus Enterococcus, whereas caecal digesta had a 227-fold greater number of the genus Ruminococcus. Acetate and iso-valerate synthesis was greater (P<0.05) for ileal fermentation than caecal fermentation, but propionate, butyrate, and valerate synthesis was lower. Short-chain fatty acids were absorbed in the GIT location where they were synthesised. In conclusion, a quantitatively important degree of fermentation occurs in the ileum of the growing pig fed a human-type diet.