Abstract: Improved ruminant’s health and its productive performance has always remained a primary goal of researchers associated with the animal production sector. Microbial feed supplements as natural growth promoters might play an important role for enhancement of health and productive performance of ruminants through prevention of disease, enhancement of desirable microbial growth in the rumen environment, stabilization of ruminal pH, altered ruminal fermentation patterns, increased nutrient digestibility and flow of nutrients to the small intestine, improved nutrient retention and reduced stress through enhanced immune response. The definition of microbial feed supplements is very broad and may include specific and nonspecific yeast, fungi, bacteria, cell fragments and filtrates. The microbial feed supplements preparations must having a beneficial effect on the host animal (non-pathogenic and non-toxic), able to produce antimicrobial agents, antagonistic toward pathogenic, have ability to adhere and colonize the epithelial cells of the rumen and the gut, capable of compete with normal microflora and metabolizing in the gut environment and genetically stable and capable of remaining viable for long periods under storage and field conditions. The use of microbial feed supplements continuously may decrease the harmful effects of the pathogenic bacterial species in the ruminant digestive system and thereby improve the animal performance.