Supplementation of ruminally protected proteins and amino acids: feed consumption, digestion and performance of cattle and sheep.

Provision of nutrients in balanced form and required amounts is essential to meet the productive targets in livestock. Among nutrients, protein plays a pivotal role in growth, production and reproduction of farm animals. However, nature and level of dietary protein determine the supply of both physiologically and dietary essential amino acids in animals. In ruminants, protein requirements are twofold; to support the anaerobic ecosystem in the rumen and to meet the animal needs. However, because of ruminal anaerobic fermentation, a portion of dietary protein is degraded in the rumen (RDP) and the rest escape from ruminal degradation (RUP). The RDP is used to support the growth of anaerobic bacteria and thus profile of microbial protein along with the nature of RUP determines the availability of dietary and physiologically essential amino acids in ruminants. Generally, the requirements of high producing animals for dietary essential amino acids are increased from those supplied by the microbial and escaped protein pool. Thus the dietary supplementation of rumen protected protein and amino acids are recommended to support the physiological and productive needs of livestock for amino acids. The objective of this article is to review all important studies on RPP, RPL and RPM and their effects on dry matter intake (DMI), digestibility and production performance of cows and sheep. Protein is an important limiting nutrient in ruminants. It contains two fractions: RDP and RUP/RPP. The rumen microbes breakdown RDP to small peptide, AA and ammonia. These, in turn, can be used for synthesis of microbial protein. The rate of microbial protein synthesis is limited by the rate of passage of feed from the rumen. Therefore, supplementation of RDP, RUP or AA is considered important to satisfy animal’s requirements. This is especially true for animals fed on poor quality forages. Supplementation of quality protein or rumen protected amino acids (RPAA) particularly Met and Lys results in increased DMI and digestibility in cattle and sheep. It also increases growth performance, reproductive efficiency and milk yield. It may have some negative effects if Met is supplied at levels substantially in excess of calculated intestinally absorbable requirements, either alone or together with Lys. Supplementation of Met may be useful in rations with low protein content fed to early lactating cows in order to prevent negative long term effects. In conclusion, supplementation of ruminally protected proteins and amino acids improved feed consumption, digestion and performance of ruminant animals fed low quality forages.