Influence of yeast culture on ruminal microbial metabolism in continuous culture.

A continuous culture study was conducted to evaluate the effect of two different yeast cultures on ruminal microbial metabolism. The treatments were a) control lactation ration, b) yeast culture 1 (YC1, Diamond-V XP) and c) yeast culture 2 (YC2, A-Max), both fed at an equivalent of 57 g/head per day. The results showed that both yeast culture products increased dry matter (DM) digestion, propionic acid production, and protein digestion compared with the control. Yeast culture 1 demonstrated an increase in molar percentage of propionic acid, a reduction in acetic acid, and a lower mean nadir (daily low) pH compared with YC2. Ruminal cultures treated with YC digested more protein and contributed less bypass N than control. Supplementing YC2 resulted in a tendency for higher microbial N/kg DM digestion than YC1. Yeast culture 1 resulted in production of rumen microbes containing less protein and more ash than YC2. These results support previous research findings that yeast culture does influence microbial metabolism, and specific yeast cultures may have different modes of action.