Yeast is a probiotic material that is currently being used in many parts of the world as a feed supplement for livestock. The use of yeast in animal feeding programmers has in many cases resulted in improved rumen fermentation, animal health, milk yield, and adaptation to heat stress. Enteric fermentation is a natural part of the digestive process in ruminant animals such as cattle, sheep, goats, and buffalo. Microbes in the digestive tract, or rumen, decompose and ferment food, producing methane as a by-product. Yeast cells produce many important fermentation metabolites and different types of important minerals and enzymes that make it useful and highly nutritive feed supplement for ruminants. It also provides improved production, reduced digestive problem, and better health in cost-effective manners. The yeasts are able to grow, at least for a short period of time, in the rumen thereby directly enhancing fiber digestion and/or producing nutrients that stimulate growth of rumen bacteria, which do the bulk of the fiber digestion.