Quantitative Effect of Excess Lysine on the Ability of Arginine to Promote Chick Weight Gain

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Abstract
A well-balanced crystalline amino acid diet was modified such that arginine was first limiting and lysine second limiting for chick weight gains. Male crossbred chicks were used in three growth assays (9 to 14 days posthatching) to determine the effect of excess lysine on the ability of arginine to promote chick weight gains (arginine efficacy). Incremental arginine supplementation of arginine-deficient diets containing from 0.55% (control level) to 2.55% dietary lysine allowed evaluation of the linear regression of chick weight gain on arginine consumption at each level of lysine. The ratio of regression coefficients (slope-ratio technique) showed that arginine efficacy decreased as dietary lysine increased. Pooled results from the three assays showed that relative arginine efficacy decreased linearly to 58.8% of the control at 1.84% dietary lysine. Higher levels of lysine caused no further decrease in arginine efficacy. A linear relationship between feed consumption and weight gain was observed which was unaffected by lysine level. Incremental additions of Quillaja saponin, an anorectic agent, to an arginine-deficient diet (0.95% lysine) did not alter arginine efficacy but did alter the relationship between feed and gain. Body water data indicated that lysine caused no change in body composition which could not be ascribed to reduced feed consumption. It is postulated that the decrease in growth rate and feed consumption observed when lysine is added to arginine-deficient diets results from accentuating the arginine deficiency.