DEGRADATION OF CONDENSED TANNINS BY RUMEN MICROBES EXPOSED TO QUEBRACHO TANNINS (QT) IN RUMEN SIMULATION TECHNIQUE (RUSITEC) AND EFFECTS OFQT ON FERMENTATIVE PROCESSES IN THE RUSITEC

In an earlier study it was observed that the rumen microbes from cattl e which had never consumed tannin-containing diets do not have enzymes for degrading condensed tannins. In this study, rumen microbes were e xposed to small amounts of quebracho tannins for 8 days using a rumen simulation technique (RUSITEC). The levels maintained in the RUSITEC w ere 0.1, 0.2 and 0.4 mg of the spray-dried quebracho powder (SDQT) per mi of the medium. After 8 days of tannin exposure, the liquor contain ing 'exposed/adapted' microbes from RUSITEC was incubated for 40 h wit hout and with purified tannins of quebracho and Dichostachys cinerea l eaves in in vitro gas method. There was no degradation of condensed ta nnins. The enzymes for degradation of condensed tannins were not induc ed in rumen microbes by exposure to different concentrations of tannin s for 8 days in the RUSITEC. In the RUSITEC, SDQT significantly reduce d the number of total protozoa, entodiniomorphs and holotrichs; effect was higher on holotrichs. There was no significant change in the leve ls of short chain fatty acid but the molar proportion of propionate wa s significantly higher and of butyrate significantly lower at 0.4 mg S DQT ml(-1). Significantly lower levels of ammonia in the medium was al so observed on injection of tannins. Microbial mass production, calcul ated using N-15 incorporation, was similar at 0.1 and 0.2 mg SDQT ml(- 1) but significantly lower (13%) at 0.4 mg SDQT ml(-1). The dry matter digestibility of the feed (80% hay and 20% barley) was not significan tly affected by SDQT.