THE EFFECTS OF INTRAVENOUS INFUSION OF LYSINE, LYSINE PLUS METHIONINE OR CARNITINE ON PLASMA AMINO ACIDS AND MILK PRODUCTION OF DAIRY COWS

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Abstract
Four lactating Holstein cows were each infused intravenously for periods of up to 9 days with solutions of L-lysine (15 g/day), L-lysine plus D,L-methionine (15 + 10 g/day) D,L-carnitine (20 g/day) or physiological saline. The cows were fed a ration of 2 kg chopped hay (14.8% crude protein), corn silage ad libitum (8.0% crude protein) and a concentrate mixture (16.5% crude protein) (1 kg/3 kg milk). Daily digestible protein intake was 1.85 kg/cow or 87% of calculated (National Academy of Sciences – National Research Council) requirements. There was no significant effect of infusion treatment on intake of corn silage, milk yield and composition or digestibility of the ration. The efficiencies of conversion of dietary protein to milk protein were 38.4, 38.6, 36.6 and 37.8% and nitrogen balances were 6, −2, 8 and 5 g/day for saline, lysine, lysine plus methionine and carnitine infusions. The concentration of carnitine in the milk was greater when carnitine was infused but was unaffected by the infusion of lysine and methionine. Plasma lysine and methionine were increased when these amino acids were infused. On the basis of plasma amino acid patterns it was concluded that methionine, lysine and threonine were possibly the most limiting amino acids under the conditions of this experiment and that in combination with a less than adequate energy intake (i.e. 87% of calculated requirements), infusion of lysine and methionine failed to give a response in production.