THE EFFECT OF DIETARY-PROTEIN LEVEL ON THE LYSINE AND ARGININE REQUIREMENTS OF GROWING CHICKENS

Comparisons were made of the growth and carcass fat responses to dieta ry lysine and of the lysine requirements of l-wk-old broiler chickens receiving diets containing either 18, 20, 23 or 25% protein. Similar c omparisons were made of the responses elicited by dietary arginine in diets containing 18 or 23% dietary protein. The responses to lysine su pplementation and the lysine requirements of chicks receiving 23 or 25 % protein diets were similar. In comparing the 18 or 20% to the 23% pr otein diet, the initial responses of growth and feed efficiency to die tary lysine were augmented, but the maximal weight gain diminished as dietary protein decreased, leading to a decrease in the lysine require ments. The amounts of extractable carcass fat or abdominal fat pad inc reased as dietary protein was lowered and, in general, were reduced ei ther by lysine or arginine supplementation. Percentage of pectoral mus cle increased slightly with dietary arginine and protein supplementati on. The results suggest that when total dietary amino acid level is re duced, the requirements for the individual amino acid decrease due to growth retardation resulting from single or multiple amino acid defici encies. Single amino acid supplementation of low protein diet is more effective in improving the amino acid balance than supplementation of high protein diets, resulting in a further decrease in the requirement s.