Effects of microbial supplements containing yeast and lactobacilli on roughage-fed ruminal microbial activities.

Effects of two microbial feed supplements on microbial activities in rumen-stimulating cultures and the rumens of steers fed a fescue hay-based roughage diet were evaluated. The yeast culture supplement contained Saccharomyces cerevisiae (1.4 to 4.2 x 10(9) colony-forming units [cfu]/g), whereas the mixed microbial supplement contained yeast, lactobacilli and enterococci (1.4 to 2.7 x 10(9) cfu/g, 1.2 to 2.3 x 10(9) cfu/g, and 1.5 to 2.6 x 10(10) cfu/g, respectively). Concentrations of viable yeast cells were increased consistently in continuous cultures and rumens of steers receiving either supplement (1 g/kg of feed). However, neither supplement consistently altered the relative concentrations of volatile fatty acids or ammonia in continuous cultures and rumens of steers. The pH tended to be greater (P = .13) in continuous cultures receiving yeast culture supplement than in cultures receiving the unsupplemented diet (6.50 vs 6.36), but pH in the rumens of steers was not affected by the supplements. Concentrations of cellulolytic microorganisms in cultures and the rumens of steers receiving supplements containing only yeast were from 5 to 40 times greater than those observed in cultures or steers receiving the unsupplemented diet. Supplements that had been treated with heat (121 degrees C for 15 min) to inactive yeast cells did not alter the concentrations of cellulolytic bacteria in rumen-stimulating cultures. These results suggest that live yeast culture supplements stimulate growth of cellulolytic microorganisms in the rumen.