Effects of the amount and quality of dietary protein on nitrogen metabolism and heat production in growing pigs.

1. Eight pigs with a mean weight of 48 kg were given, at a constant daily rate, diets of low (0.15) or high (0.30) protein content, very deficient in lysine, with or without a supplement of L-lysine (3.7 g/kg). 2. Measurements of nitrogen and energy metabolism were made in four successive 14 d periods in a Latin-square design. 3. The rate of protein accretion was substantially increased by increases in both protein and lysine supply, but the rate of heat production was not significantly changed. 4. The rate of fat deposition varied inversely with the rate of protein accretion, being reduced by both protein and lysine supplements. 5. The relation between heat production and protein accretion (allowing for a constant energy cost of fat deposition) suggested that heat production increased with additional protein accretion less when protein quality was improved than when more protein was given.