EFFECTS OF AMINO-ACID BALANCE AND ENERGY-PROTEIN RATIO ON ENERGY AND NITROGEN-METABOLISM IN MALE BROILER-CHICKENS

1. An experiment was performed with growing broiler chickens (14 to 21 d old) to examine 3 diet characteristics which have been implicated i n regulatory elevation of metabolic rate: an imbalanced amino acid mix ture, high dietary energy concentration and low protein concentration. 2. Differences in energy expenditure could be explained almost entire ly (93%) by differences in quantities, and therefore costs, of protein and fat accretion. There was no indication of regulatory diet-induced thermogenesis. Heat production was not significantly correlated with CP:TME ratio and was negatively correlated (P<0.01) with dietary TME c oncentration. 3. Heat production was closely correlated (P<0.001) with rate of protein accretion, which in turn was more strongly associated with intake of the first-limiting amino acid (lysine) than with total protein intake. Heat production on an imbalanced, lysine-limited, ami no acid mixture was no greater than on a balanced amino acid source wi th the same lysine concentration. 4. There was no indication of a stim ulation of heat production by excess amino acids. Heat production, adj usted for body weight by covariance analysis, was similar on paired di ets which had identical lysine concentrations but a 1.5- or 2-fold dif ference in crude protein concentration. 5. There was a strong negative correlation (P<0.001) between protein retention per g of lysine consu med and lysine:CP ratio, suggesting that, in this case, response to a limiting amino acid was improved by the presence of a super-abundance of other amino acids.