Based on our understanding of ruminal fermentation, nutritionists and microbiologists try to formulate diets or develop feed supplements to manipulate the fermentation and increase the efficiency of production. Over the years, various techniques have been explored including dietary supplementation with ionophores, direct fed microbial products (yeast and fungi), or organic acids. Two of these approaches were further explored in my thesis 1) an investigation of the concentration of malate in a variety of ensiled forages and 2) the effects of Saccharomyces cerevisiae live cell yeast and yeast culture on in, alfalfa hay, and Coastal bermudagrass hay.