Enzymes and direct fed microbials in diets for dairy cows

Direct-Fed microbials (DFM) contain live bacteria and yeast; others contain bacterial and fungal crude extracts or fermentation byproducts. Feed enzyme products for ruminants are refined extracts of bacterial and fungal origin that have an array of fibrolytic enzyme activities. Often, there is confusion over the differences between enzyme and DFM products because many DFM products are marketed, at least partly or implicitly, on their residual enzymatic content. However, in comparison to enzyme products, DFM products contain relatively little actual fibrolytic enzyme activity. Numerous DFM products are commercially available, while ruminant feed enzymes are just now entering the marketplace. Both DFM and feed enzyme products have been shown to enhance fiber digestion by ruminants, but the mechanism whereby they increase feed utilization differs. On the whole, responses in animal performance to DFM and feed enzyme products have been somewhat inconsistent. Production responses to DFM and enzymes can be attributed mainly to improvements in energy availability. Thus, animal responses will be greatest in situations in which fiber digestion is compromised and when energy is the first limiting nutrient. Furthermore, as with any new feed product, there is variability in the response when supplementation is viewed across all products. With increasing consumer concern about the use of growth promoters and antibiotics in ruminant production, and the magnitude of increased animal performance obtainable using feed enzymes and DFM, there is no doubt that these products will play an important role in future ruminant production. A more complete understanding of the mode of action of these products will allow us to use enzymes and DFM to obtain the desired effects.