Free amino acids in blood of ruminants--physiological and nutritional regulation.

Tissue free amino acid pools account for only a small fraction of the total amino acid content in the body. Blood of plasma free amino acid pools represent only a very small proportion of tissue free amino pools. Plasma free amino acid profiles have been used as a tool to study nutritional and metabolic aspects of protein status. Static measurements of plasma amino acid levels have limited value as sensitive indicators of protein status because such measurements do not reflect the magnitude of amino acid fluxes in and out free amino acid pools. Use of plasma amino acid profiles, under well defined experimental conditions, in assessing limiting amino acids and essential amino acid requirements in ruminants is discussed.