The optimum ratio of standardized ileal digestible leucine to lysine for 8 to 12 kg female pigs

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.