Dietary Applications of Exogenous Enzymes to Improve Nutrient Utilization and Performance in Ruminants

Competition among animal feeds, human foods, and demands for biofuel production forces livestock producers to feed their animals on the available low-cost raw materials. Ruminant farmers provide their animals forage-based diets to reduce the cost of feeding and to keep normal rumen function. However, only forage feeding does not sometimes provide animals enough available energy and protein required for milk production and growth. The major problem with feeding low-quality forages or raw materials is their content of rigid and less-digestible cell wall components. However, ruminants have a digestive system with a complex and dynamic microbiota and microbial activities that allow them to utilize plant cell walls and degrade them to be utilized as energy sources by host. The ability of ruminants to degrade structural polysaccharides (e.g., cellulose, hemicellulose, and lignin) has a limit, and under perfect conditions, is less than 65%. Different approaches have been developed to improve nutrient digestibility and production responses in ruminants including chemical, physical, and biological strategies. Exogenous enzymes have gained an increasing interest to improve the nutritive value of ruminant feeds. The aim of administration of exogenous enzymes is to improve fiber degradation and efficiency of feed utilization by enhanced nutrient utilization and reduce the wastage. Exogenous enzymes are capable of breaking down specific bonds in carbohydrates, starch, protein, fats, cellulose, hemicellulose, pectin, glycoproteins, and lignin. Lactobacillus acidophilus, L. plantarum, Streptococcus faecium, and Bacillus subtilis are the main bacterial species that produce a wide array of exogenous enzymes, while Trichoderma reesei, Aspergillus oryzae, and Saccharomyces cerevisiae are the main fungal enzyme producers. The ability of exogenous enzymes to improve growth performance in feedlot cattle and small ruminants as well as milk production in dairy cattle has been demonstrated, but with inconsistent effects. Enzyme type and preparation, application method, level of enzyme supplementation, diets, animals and interaction between enzymes and feeds are the factors that determine the response to enzyme supplementation and are responsible for variations among experiments. This chapter reviews information about sources of enzymes, enzyme activity, modes of action, optimal inclusion, and response of ruminant to dietary applications of various enzymes.