Metabolism of Amino Acids in the Bovine Rumen

Abstract

Summary Catabolic intermediates of l-arginine, l-lysine, and dl-tryptophan in vivo were compared with previously determined dissimilation products of these amino acids in vitro. The relative concentrations of amino acids and amines of jugular vein-blood plasma were examined at 0, 1, 2, and 4 hr after administration of each amino acid, and rumen ingesta was assayed for amino acids, ammonia, indole, and skatole for a 24-hr period. dl-tryptophan (265.5g), l-arginine · HCl (274g), or l-lysine · HCl (237g) dissolved in one liter of water was mixed with the rumen ingesta of one of two rumen-fistula cows 2 hr after feeding 12lb hay and 8lb grain. Rumen ammonia concentrations were the largest 6 hr following arginine administration (32mg NH 3 -N/100ml), whereas tryptophan and lysine yielded smaller, but detectable, amounts of ammonia. Arginine yielded ornithine; the ruminal concentration of these two amino acids became equal within 6 hr after arginine administration. The ruminal lysine concentration decreased 50% within 6 hr of administration and this decrease was accompanied by an increase in delta-amino valeric acid concentration. Ruminal tryptophan concentrations were not markedly reduced until 8 to 10 hr after administration, at which time indole and skatole concentrations were 3 to 5 μ g/ml rumen fluid. Plasma indole and skatole did not exceed 0.25 μ g/ml through 4 hr. Arginine and lysine supplementation increased the concentration of several plasma amino acids within 1 hr after addition to the rumen, whereas tryptophan had little or no effect. Plasma lysine was markedly increased 4 hr after lysine administration.