Production of cellulase is of great significance in present day biotechnology. Cellulose biodegradation by cellulases, produced by numerous microorganisms is very important in several agricultural and waste treatment processes. The development of microbial strains, media composition and process control has including submerged fermentation and solid state fermentation all contributed to achievements of high levels of cellulases for subsequent applications. One of these important applications is supplementing diets of farm animals with cellulases to improve feed utilization and animal performance by enhancing fiber degradation. Dairy cows feed forge treated with a cellulase enzyme preparations ate more feed and produced 5-25% more milk. This review provides an over view of the main variables to be considered for cellulase production from agricultural residues for animal feeding.