ASSAY AND DIGESTION OF C-14-LABELED CONDENSED TANNINS IN THE GASTROINTESTINAL-TRACT OF SHEEP

Three experiments mere conducted to determine the fate of condensed ta nnins (CT) during digestion in sheep. CT were measured as extractable, protein-bound and fibre-bound fractions using the butanol-HCl procedu re. In Expt 1, purified CT were added to digesta from different parts of the digestive tract obtained from a pasture-fed sheep. Recoveries o f CT after 0 and 4 h of anaerobic incubation at 39 degrees averaged: r umen 78.9 and 57.5%; abomasum 50.9 and 49.0%; duodenum 64.4 and 46.0% and ileum 43.4 and 38.8%. In Expt 2, [C-14]CT was given per abomasum o ver a 6.5 h period at 15 min intervals to a sheep previously fed on Lo tus pedunculatus (which contains CT). The sheep was killed at the end of the period and 92.4% of the label was recovered. Virtually all of t he label was in the digesta, and none was detected in the blood, so th at the CT-carbon appeared not to be absorbed from the small intestine. In Expt 3, rumen, abomasal and ileal digesta and faeces samples from sheep fed on Lotos pedunculatus were analysed for CT and CT flow along the digestive tract calculated from reference to indigestible markers . Values were low in all digesta samples, indicating disappearance of CT across the rumen and small intestine, and CT recovery in faeces was only about 15% of intake. However, the C-14 results from Expt 2 sugge sted that little if any CT-carbon was absorbed and the low recoveries in Expt 1 are considered to be a consequence of either conformational changes to the CT molecule such that it is no longer detectable by col orimetric methods, an inability of the analytical method to release bo und CT for the butanol-HCl assay, or interference from other digesta c onstituents. It is concluded that the butanol-HCl method of CT analysi s is appropriate for quantifying CT in herbages but not in digesta or faeces, and that a substantial part of CT released during protein dige stion in the small intestine may not be detectable by normal CT analyt ical methods.