Failure of Excess Dietary Lysine to Antagonize Arginine in Young Pigs

Abstract

Experiments were conducted with young pigs to evaluate the effects of excess lysine when added to diets marginal in arginine. The basal diet was formulated to contain 1.15% lysine and 0.53% arginine. Lysine levels above this were achieved by incremental additions of L-lysine·HCl (experiment 1) or L-lysine acetate (experiment 2). Neither weight gain nor gain-feed ratio was lowered in pigs fed twice the recommended level of lysine (i.e., 2.30%). Lysine levels three or four times the basal level, however, lowered both weight gain and feed intake with no commensurate reduction in feed efficiency. Therefore, lysine appeared to reduce growth via amino acid imbalance rather than antagonism. In pigs equally fed isonitrogenous diets, urea N excretion in the urine was lower in those fed 3.45% supplemental lysine (4.6% total lysine) than in those fed the basal diet. This was offset by a dramatic elevation in urinary excretion of basic amino acids. Urinary excretion of lysine accounted for 26.2% of the lysine consumed by pigs fed 3.45% supplemental lysine. Free lysine levels as well as α-aminoadipic acid levels were markedly higher in plasma, liver, kidney and muscle of pigs fed excess lysine than in those fed the basal diet. Tissue levels of arginase and ornithine transcarbamoylase were uninfluenced by the level of lysine ingested.