Efficacy of plant extracts rich in secondary constituents to modify rumen fermentation

Three plant extracts with different secondary constituents were simultaneously evaluated in an eight fermenter rumen simulation technique (Rusitec) for their effects on ruminal fermentation pattern. Specifically, a Yucca schidigera extract containing the saponin compound sarsaponin was supplied at three concentrations (1, 20 and 100 mg sarsaponin/kg dry matter (DM)) and was compared to a Castanea sativa wood extract containing hydrolysable tannins (0.5 and 2.5 g tannins/kg) and pure sulphonate-free lignin (2.5 g/kg). The supplements were added to a basal diet (grass silage, barley grain, grass hay) with a low crude protein (CP) content. These diets were compared to the same, unsuppplemented basal diet (control) and to a diet with additional soybean meal providing protein according to recommendations for dairy cow diets. The control diet and the soybean meal diet differed in rumen fluid ammonia concentration by 15% (13.6 mmol/l versus 16.0 mmol/l). Relative to the control diet, the high doses of the saponin-rich and the tannin-rich extract reduced the rumen fluid ammonia level by up to 21%. There was a tendency for elevated levels of apparent protein degradation during 48 h of fermentation, suggesting that the effect of the extracts on ammonia probably did not result from suppression of microbial protein degradation. Bacterial and protozoal counts in rumen fluid were not influenced by dietary treatments. Substantive effects of the saponin-rich and tannin-rich products on ruminal nitrogen metabolism were observed only at doses exceeding those recommended by the manufacturers.