Effects of live yeast (Saccharomyces cerevisiae) and type of cereal on rumen microbial fermentation in a dual flow continuous culture fermentation system

Live yeast additives may help optimize ruminal fermentation of high-grain diets, especially when the starch of the ration is highly fermentable. Eight dual flow continuous culture fermenters were used in a 2 × 2 factorial design in two replicated periods of 9 days (six for adaptation and three for sampling) to determine the effect of live yeast and type of cereal on rumen microbial fermentation and nutrient digestibility. Main factors were the addition of live yeast: no yeast (NY) vs. 2 × 10⁷ CFU of yeast/g of diet (LY); and type of cereal in the diet: corn (CO) vs. barley (BA). All fermenters were fed 80 g dry matter/day of a 10-90 forage to concentrate diet and pH was allowed to fluctuate with an upper (6.6) and lower (5.5) limit. Treatment BA increased OM digestion, valerate proportion, peptides and ammonia N fractions, ammonia N flow, crude protein degradation and target copies of Megasphaera elsdenii; and decreased NDF digestion, propionate proportion, branched-chain VFA (BCVFA) concentration, AA-N fraction and nonammonia N flow. Treatment LY increased BCVFA and decreased ammonia N fraction and flow, and the target copies of Streptococcus bovis. Treatment LY decreased the slope of pH drop, the area under pH 6.0 and the gas production. These results suggest potential benefits of LY in stabilizing the fermentation of BA-based diets.