Influence of dietary condensed tannin on microbial crude protein supply in sheep

Excessive intakes of condensed tannin (CT) are associated with a reduction in N retention in ruminants. It is commonly presumed that part of this reduction is explained by an inhibitory effect of CT on the production of microbial crude protein (MCP). Recent data from our group questions this presumption. Neutralisation of CT in Leucaena foliage, by supplementing sheep fed Leucaena with the tannin-neutralising agent polyethylene glycol (PEG), induced no change in MCP production. Similarly, MCP production remained unchanged when sheep fed lucerne hay were supplemented with increasing amounts of Quebracho CT. Some decline was observed when MCP production was compared in sheep fed Leucaena genotypes differing in CT content. The less than expected effects of CT at the level of the rumen lend support to the hypothesis that CT exert their major effects post-ruminally.