The objective of the study was to estimate Leu requirement for weaned piglets to balance indispensable AA in reduced CP diets. A dose-response experiment was conducted to estimate the standardized ileal digestible (
SID) Leu to Lys ratio required for the maximum growth of young pigs after weaning. In this study, 96 female pigs (initial BW of 8 kg) were allotted to 1 of 6 dietary treatments with 16 individually penned pigs per treatment. Graded levels of crystalline L-Leu were added to a basal diet to provide diets containing 0.70, 0.80, 0.90, 1.00, 1.10, and 1.20
SID Leu:Lys.
Lysine was limiting and fulfilled 90% of the current recommendations. The ADFI, ADG, and G:F were determined during a 2 wk experimental period. Blood and urine samples were taken at the end of each wk. The ADFI increased linearly (P < 0.001) from 0.70 to 0.80
SID Leu:Lys and then remained constant from 0.90 to 1.20
SID Leu:Lys. The ADG showed a quadratic increase ( P= 0.02), as the
SID Leu:Lys level increased from 0.70 to 0.90
SID Leu:Lys and did not change further from 0.90 to 1.20
SID Leu:Lys. The G:F increased quadratically (P < 0.001) with increasing
SID Leu:Lys level, and the greatest G:F was achieved with pigs receiving the diet with 0.80
SID Leu:Lys. Increasing the dietary
SID Leu:Lys resulted in a linear increase in plasma Leu concentration (P < 0.001) and quadratic increases (P < 0.001) in plasma Cys concentration. The plasma concentration of most of the other AA was lowest in pigs receiving the diets with 0.90 to 1.00
SID Leu:Lys. The plasma
urea nitrogen concentration tended (P = 0.08) to be lowest in pigs receiving 1.00
SID Leu:Lys, suggesting a more balanced AA profile at this level. Using a curvilinear-plateau model, the
SID Leu:Lys requirement was estimated at 0.93 to maximize growth in female pigs weighing 8 to 12 kg.