Synthetic Amino Acids Administered to Cattle: Disappearance from the Rumen and Appearance into the Circulating Blood

Abstract

Single administration of DL-methionine (MET), L-lysine monohydrochloride (LYS) or L-tryptophan (TRP) into the rumen of 290-480kg heifers at graded doses of 0.12, 0.20 and 0.60g/kg body weight resulted in an increase of pertinent amino acids in plasma except at the lowest dose of LYS and TRP. At the highest doses, each amino acid was detected in a high concentration from the rumen for more than 16h. Half-lives of disappearance in the in vitro culture were 3.4, 5.6 and 1.8h respectively when 0.1mg each of MET, LYS and TRP were added per ml rumen fluid, while 34.7, 30.1 and 38.5h, respectively, when added at the level of 2.0mg/ml, suggesting that the disappearance rate of each amino acid is dose-dependent. Supplying with 50g each of MET or LYS to about 300kg heifers at 12h-intervals for successive 15 days did not cause an increase in the plasma concentration of pertinent amino acids after 5 days, although the increase was detected at least after the first administration. Progressive increase of ruminal metabolic activity accompanying with the successive administration of MET or LYS was suggested in vivo and supported by the progressive decrease in in vitro half-lives of disappearance when each amino acid was incubated with rumen fluid taken from the heifers with the lapse of time during the successive administration.