Amino acid requirements and amino acid supply in the sheep

The special features of nitrogen metabolism in ruminants, which stem from the extensive breakdown and synthesis of dietary protein in the rumen (see Hungate, 1966), imply the absence of a specific dietary requirement for essential amino acids.Nevertheless, there is considerable theoretical and practical interest in defining the amino acid requirements of ruminant tissues in animals of known nutritional and physiological status.Direct methods of measurement based on the growth or production response of animals to varying intakes of amino acids are clearly inapplicable, and it is necessary to use indirect procedures.The successful development of re-entrant fistulas has made it possible to measure the uptake of amino acids from the small intestine and to use the duodenal fistula to supplement amino acid supply.In this paper methods of measuring amino acid requirement in sheep based on the changes in plasma amino acid (PAA) concentration or oxidation in response to different levels of amino acid supply are discussed in relation to quantitative results of amino acid uptakes obtained using re-entrant intestinal fistulas.