Effects of Saccharomyces cerevisiae and Aspergillus oryzae cultures on ruminal fermentation in dairy cows.

Four lactating Holstein cows, fitted with ruminal and duodenal cannulas, were used in a 4 x 4 Latin square design to examine the effects of supplemental yeast (Saccharomyces cerevisiae) and fungal (Aspergillus oryzae) cultures on ruminal fermentation, microbial populations, and nutrient supply to the small intestine. Cows were fed a basal diet comprising 32.5% corn silage, 17.5% alfalfa hay, 35.3% corn grain, 12.7% soybean meal, and 2% vitamin and mineral mixture on a DM basis. Treatments were arranged in a 2 x 2 factorial as follows: 1) basal diet, 2) basal diet plus 57 g/d of yeast culture, 3) basal diet plus 3 g/d of fungal culture, and 4) basal diet plus 57 g/d of yeast culture and 3 g/d of fungal culture. Ruminal pH, ammonia N concentration, and total VFA concentration were similar among treatments. Molar percentages of ruminal isoacids were lower for cows fed a mixture of yeast and fungal culture than for cows fed yeast or fungal culture alone. Yeast culture increased ruminal OM and CP digestion and decreased OM and N flow to the duodenum. Fiber digestion in the rumen was similar among treatments. Fungal culture stimulated proteolytic and cellulolytic bacterial counts. Proteolytic bacterial counts were also stimulated by yeast culture. Results from this experiment demonstrated that yeast and fungal cultures could influence ruminal fermentation and microbial populations.