Exogenous Enzymes in Ruminant Nutrition: A Review
The concept of supplementation of ruminant diets with exogenous enzymes is not new though a considerable research interest on this field has been emerged from 1990s. Availability of wide range of exogenous enzyme products, development of better methods to evaluate enzyme activity, revised knowledge on rumen functions and recent advances of biotechnology which lowers the cost of enzyme production have fuelled the enzyme utilization in ruminant industries. The exogenous enzymes used in ruminant diets can be characterized in to main categories as fibrolytic, amylolytic and proteolytic based on specific substrate on which their enzyme activity can perform. The sources of these exogenous enzymes are mainly four bacterial species, three fungal species and some yeasts. Solid State Fermentation (SSF) and Submerged Fermentation (SmF) are the major methods for enzyme extraction which have combined with several other biotechnological aspects. The enzyme application method can vary in a wide range from applying to forage at harvesting, at ensiling, at feeding and the portion of feed which is mixed with enzyme may also vary from to forage to concentrate to a part of totally mixed rations. Up to date numerous number of researches have been done with ruminants like cattle both dairy and beef, goat, sheep and less with buffalo. The results seems to be inconsistent but positive results on feed intake, nutrient digestibility, growth performance, other production parameters, manure nutrient excretion etc., have been obtained. Therefore more fine-tuned research efforts are highly suggested for the generalization of exogenous enzyme usage in ruminant nutrition.
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