The Lysine and Total Sulfur Amino Acid Requirements of Six- to Twelve-Kilogram Pigs

Three experiments were conducted to determine the Lys and TSAA requirement of 6- to 12-kg pigs. There were 5 replications of 5 or 6 pigs per pen (for Exp. 1, 2, and 3, n=150, 150, and 168 with initial BW of 6.3, 6.7, and 6.4kg and final BW of 10.8, 11.7, and 11.2 kg, respectively). In Exp. 1, pigs were fed in a 13-d growth assay and treatments were: positive control (PC, 40% corn, 38% soybean meal, 10% whey, 3% fish meal, 3% fat, and 1.45% true ileal digestible (TID) Lys), and TID Lys levels of 1.1, 1.2, 1.3, 1.4, and 1.5%. The addition of Lys increased G:F (linear, P < 0.05), ADG (linear, P < 0.05; quadratic, P < 0.05), and ADFI (linear, P < 0.05; quadratic, P < 0.10). Growth performance of pigs fed the 3 highest levels of Lys was not different from those fed the PC diet. Plasma urea N (PUN) decreased linearly (P < 0.001) with the addition of Lys. Break point analysis estimated requirements of 1.43 and 1.41% for ADG and PUN, respectively. In Exp. 2, pigs were fed in a 14-d growth assay and treatments were PC (similar to that in Exp. 1; 0.88% TID TSAA), and TID TSAA levels of 0.62, 0.68, 0.74, 0.80, and 0.86% with a TID Lys level of 1.35%. There was no response of increasing TSAA from 0.62 to 0.86%. In Exp. 3, pigs were fed in a 13-d growth assay and treatments were PC (same as Exp. 2) and TID TSAA levels of 0.52, 0.58, 0.64, 0.70, and 0.76% with a TID Lys level of 1.35%. The addition of TSAA increased ADG (linear, P < 0.05; quadratic, P < 0.05) and decreased PUN (linear and quadratic, P < 0.001). However, pigs receiving the basal diet with varying levels of TSAA had lower ADG (P < 0.05) and G:F (P < 0.001) than pigs fed the PC diet. Break point analysis estimated requirements of 0.58 and 0.56% TID TSAA for ADG and PUN, respectively. Data from these experiments suggest the TID Lys requirement is 1.40% or 18.90mg TID Lys/g gain for 6- to 12-kg pigs, and the TID TSAA requirement is near 10.14mg TID TSAA/g gain, resulting in a TSAA:Lys ratio that is approximately 0.54.