Mode of action of exogenous cell wall degrading enzymes for ruminants

Abstract

Recent studies have shown that adding exogenous fibrolytic enzymes to ruminant diets can increase milk production of dairy cows and weight gain of growing beef cattle as a result of enhanced feed digestion. While much progress has been made in terms of advancing feed enzyme technology for ruminants, considerable research is still required to develop more effective enzyme products. The mode of action whereby exogenous enzymes improve digestion of plant cell wall is complex, and there is evidence for numerous potential modes of action suggesting they are interdependant. A mode of action that accounts for the most critical factors that explain the observed increases in feed digestion is presented. Adding exogenous enzymes to the diet increases the hydrolytic capacity of the rumen mainly due to increased bacterial attachment, stimulation of rumen microbial populations and synergistic effects with hydrolases of ruminal microorganisms. The net effect is increased enzymic activity within the rumen, which enhances digestibility of the total diet fed. Thus, improvements in digestibility are not limited to the dietary component to which the enzymes are applied, which explains why fibrolytic enzymes can be effective when added to supplement or grain. The magnitude of the improvements in feed digestibility reported in some research studies using feed enzymes suggests a viable future for enzyme products in commercial ruminant production systems. A more complete understanding of the mode of action of these products will allow development of low-cost enzyme products designed specifically to improve feed digestion by ruminants. Key words: Cattle, digestion, fibre digestion, enzymes, cellulases, hemicellulases