Amino acid metabolism in the piglet. 3. Influence of lysine level in the diet on energy metabolism and in vivo oxidation.

Abstract

1. Supplementing a lysine-deficient diet (5 g lysine/kg) with five increments of lysine, each of 2 g/kg, resulted in increased in growth rate of Yorkshire piglets, aged between 3 and 7 weeks, up to the highest level of lysine (15 g/kg). 2. The free lysine concentration of plasma tended to increase as the dietary lysine level increased from 13 to 15 g/kg, and plasma threonine concentration decreased significantly as the lysine content of the diet was increased from 11 to 15 g/kg indicating that threonine was the second limiting amino acid in the diet. 3. Oxygen consumption and carbon dioxide production of the piglets were not influenced by supplementing the diets with lysine. The heat production was 0-313 kJ/min per kg body-weight in the 6 h experimental period. 4. Supplementation of the diet with lysine had no consistent effect on the recovery of 14C as 14CO2 from a single dose of L-[U-14C]lysine. 5. Adjustment of the determined recoveries of the tracer dose of lysine for the differences in the plasma concentrations of free lysine for the pigs receiving the graded levels of dietary lysine simplified the relationship between recovery and dietary lysine level: it was linear for the first four increments in dietary lysine and then increased sharply for the fifth increment. This indicated that a marked change in the rate of lysine catabolism occurred as the level of dietary lysine was increased from 13 to 15 g/kg. 6. The results of this experiment indicate that the piglets' requirement for lysine is between 13 and 15 g lysine/kg in a diet which contained 181 g crude protein (nitrogen X6-25)/kg.