Effects of a Saccharomyces cerevisiae culture on in vitro mixed ruminal microorganism fermentation

Previous research has shown that Saccharomyces cerevisiae culture increases lactate utilization and cellulose digestion by pure cultures of ruminal ba cteria. Based on these pure culture results, in vitro mixed ruminal microor ganism fermentations were conducted to determine the effects of 0.35 and 0. 73 g/L of Sacc. cerevisiae culture on the fermentation of ground corn, malt ose, alfalfa hay, bermudagrass hay, and lactate. In addition, experiments w ere performed to evaluate the effects of Sacc. cerevisiae culture and monen sin on the mixed ruminal microorganism fermentation. In the presence of gro und corn, both concentrations of Sacc. cerevisiae culture had little effect on final pH or fermentation products, except the 0.35 g/L treatment increa sed valerate concentration. Saccharomyces cerevisiae culture had little eff ect on final pH or fermentation products in maltose or lactate fermentation s. When alfalfa hay was the substrate, 0.73 g/L of Sacc. cerevisiae culture increased propionate concentration and both treatments decreased the aceta te to propionate ratio. In the case of Coastal bermudagrass hay, 0.73 g/L S acc. cerevisiae culture increased concentrations of acetate, propionate, CH 4, butyrate, isovalerate, valerate, and decreased the acetate to propionate ratio, whereas both treatments increased total volatile fatty acid concent rations. Similar to alfalfa hay, in vitro dry matter disappearance of Coast al bermudagrass hay was numerically increased in the presence of Sacc. cere visiae culture. Monensin altered the fermentation by decreasing concentrati ons of CH4 and lactate and increasing concentrations of propionate. There w as no interaction between Sacc. cerevisiae culture and monensin. In conclus ion, the incorporation of Sacc. cerevisiae culture into mixed ruminal micro organism fermentations of ground corn, maltose, or lactate had little effec t on final pH and fermentation products. However, in the presence of alfalf a hay or Coastal bermudagrass hay Sacc. cerevisiae culture increased concen trations of several fermentation products and numerically increased in vitr o dry matter disappearance of forage fiber.