Predicting the Impact of a Live Yeast Strain on Rumen Kinetics and Ration Formulation

Yeast additives have been fed to animals for more than 100 years. Although there are about 500 different species of yeast, the most common one fed to cows is Saccharomyces cerevisiae. Strains of Saccharomyces cerevisiae on the market today vary widely. The American Association of Feed Control Officials defines an active dry yeast as containing no less than 15 billion live yeast cells (cfu) per gram, being dried to preserve its fermenting power, and containing no filler product (e.g Levucell SC I-1077). Unlike active dry yeast, yeast culture products are defined as containing yeast and the media on which it was grown. Some yeast culture products contain live cells, where as other yeast culture products do not guarantee any live yeast cells in their product. They may also contain a carrier such as rice hulls. They rely on dead yeast cells, the media the yeast was grown on, and metabolites made by the yeast cell during the manufacturer’s fermentation process to have a positive effect on rumen fermentation.