The digestion of dietary protein bound by condensed tannins in the gastro-intestinal tract of sheep

The digestion of dietary protein bound by condensed tannins (CTs) in ruminants was investigated by determining the extent of dissociation of insoluble 125I-BSA + CT complexes administered to abomasally and intestinally fistulated sheep. The extent of dissociation was registered as the true digestibility of iodinated bovine serum albumin (125I-BSA). The true digestibility of 125I-BSA originally bound to Leucaena pallida CT (0.721) was lower (P<0.05) than that of 125I-BSA originally bound to L. leucocephala CT (0.880) between the abomasum and terminal ileum. These results indicate that differences in the ability of CT to inhibit 125I-BSA digestion in vivo matched the relative abilities of the same CT to bind BSA in vitro, indicating that the in vitro BSA-binding assay for ranking CT behaviour was biologically relevant in vivo. Furthermore, the true digestibility of CT-bound 125I-BSA between the mouth and faeces permitted the prediction of the quantitative contribution that CT-bound dietary proteins make to improved nitrogen supply to the small intestines.