AMINO-ACID-METABOLISM IN RUMINANTS

All animals require amino acids (AA) which are the building blocks of proteins required for optimal growth, reproduction, lactation, and mai ntenance. In ruminants, proteins and AA are first subject to microbial degradation in the rumen making it difficult to predict the quality a nd quantity of AA that are absorbed by the animal. In ruminants, absor bed AA comes from microbial protein synthesis in the rumen and from di etary amino acid sources that are undegraded in the rumen, Production of microbial protein alone is insufficient to supply adequate amounts of amino acids for optimal production. In cattle, methionine and lysin e are generally the first limiting AA for production. Improving the qu ality of absorbable AA can be accomplished through several means. For example, feeds can be chosen whose proteins are relatively resistant t o rumen degradation. However, this does not ensure overcoming the limi ting AA. A better method would be to predict which AA were limiting an d then to supply these AA in a rumen protected form. The future of und erstanding requirements of AA for ruminants will rely on the ability o f models to accurately predict the need for supplemental AA.