author(s)
Sundus F Mohammed, Firas A Mahmood and Enas R Abas

abstract
Feed additives are groups of feed ingredients that are required in quantity and can cause desired animal response. In the past two decades, the potential roles of using products containing living microorganisms as specific microbial supplements have been better feed supplements for ruminants. Feed additives are useful for dairy producers to improve nutritive value of the diets for dairy animals and increased profits when used correctly. Additives should be viewed as enhancements of good feeding programs and it should not be considered as replacements of balanced rations and good feeding practices. The work on feeding yeast as probiotic was initiated as early as 1950's, although yeast biomass as a byproduct of alcohol industry was earlier used as a protein source. Yeast, which was later named as probiotic, was used only at a lower level as a feed supplement. The use of Saccharomyces cerevisiae (Sc) asa Probiotic when added to feed in small amounts began during the 1940’s and 1950’s. Data indicate that supplementation of yeast to the ruminant diet may improve feed intake weight gain and productivity, digestion and numbers of anaerobic cellulytic bacteria, and ruminal PH value. Also, italter the patterns of volatile fatty acids and influence absorption of some minerals.