Abstract/Summary

The fate of condensed tannins (CTs) along the digestive tract of ruminants is not well known and may account for the variable efficacy of CTs against gastrointestinal nematodes in different locations. Here, we analyzed sainfoin CTs in the digesta of cattle from two separate experiments. When using the acetone-butanol-HCl assay, the total CTs concentrations in the digestive tract were close to those in the diets (6.3 and 1.5% of DM in Expt. 1 and 2, resp.) indicating that CTs remained largely undegraded and unabsorbed. Yet with the thiolysis assay in Expt. 1, CTs concentration was much higher in the abomasum (2.3 ± 0.4 % of DM) compared with the rumen, small and large intestines, along with increases of mean size and percentage of prodelphinidins within CTs. This corroborates the anthelmintic efficacy reported only against Ostertagia ostertagi in the abomasum. In Expt. 2, no anthelmintic effect was observed against the larval exsheathment in the rumen, probably because the dietary level of CTs was too low. Overall, the level of CTs accessible to thiolysis in the gut appears to be critical for anthelmintic activity, which is favored under the acidic conditions of the abomasum.