The use of exogenous enzymes as dietary supplements in dairy cow nutrition

This chapter summarises the effects of supplementing exogenous enzymes on improving efficiency of nutrient utilization in dairy cows by reviewing the research on enzyme selection, animal responses to feed enzymes, and the mechanisms of improving nutrient utilization. Exogenous fibrolytic enzymes, amylases, and proteases have potential to increase the rate of nutrient utilization, consequently, improve animal performance; however, the responses to application of fibrolytic enzymes have been equivocal and variabilities may be attributed to differences in the experimental conditions, activities of the supplemented enzymes, and inappropriate mode of application. Application of fungal enzymes from white-rot fungi with lignin-degrading activities and expansin-like proteins may be an effective way to improve efficacy of fibrolytic enzymes; however, in vivo validation is required. The role of metagenomics and metatranscriptomics would be crucial for better understanding of the actual requirement for enzymes and the functional genomic framework within which the rumen operates.