Mg. Macleod, EFFECTS OF AMINO-ACID BALANCE AND ENERGY-PROTEIN RATIO ON ENERGY AND NITROGEN-METABOLISM IN MALE BROILER-CHICKENS, British Poultry Science, 38(4), 1997, pp. 405-411
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.