The influence of a change of colonic availability of biotin on biotin status was studied. This was done by inhibition of biotin absorption by intracaecal avidin infusion. Five adult minipigs with a permanent caecal ‘T’ cannula were fed on a semi-synthetic, biotin-deficient diet for 4 months. Following an 8-week adaptation period there were nine sequential 1-week infusion periods with or without oral lactulose or antibiotics. Avidin infusion during weeks 2, 5 and 8 amounted to 18 mg/d (13 U/mg). Plasma biotin concentrations were not changed by avidin infusions. There was a significant average 84% rise in faecal biotin excretion during the avidin periods. Urinary biotin output following avidin decreased by 21 %. This is taken as evidence that biotin synthesized by colonic bacteria is available for host metabolism. A rough estimate shows that under basal conditions 1.7–17% of the metabolic allowance may be covered by this metabolic route.

Eight pigs were given a semi-purified diet based on maize flour and casein containing 10 μg biotin/kg. The diet was given ad lib. with or without a supplement of 70 μg biotin/kg diet from 5 to 94 d of age. The flow of biotin in the stomach was similar to the biotin intake (13.5 and 112 μg/d) for the unsupplemented and biotin-supplemented pigs respectively. The flow of biotin through the small intestine decreased for the biotin-supplemented pigs from 39 μg/d in the first quarter of the small intestine to 7.9 μg/d in the last quarter. The flows of biotin in the caecum, large intestine and colon were similar for both the unsupplemented and biotin-supplemented pigs, with values of 17–54 μg/d, indicating the synthesis of biotin in the hind-gut.