The standardized ileal digestible isoleucine to lysine requirement ratio may not be greater than 50% in post-weaned piglets

The branched-chain amino acids (BCAA) Ile and Val are potentially limiting amino acids for growth in pigs. Although reports exist concerning the Ile requirement, results seem to vary with the BCAA content of the diet. The purpose of this study was to determine the response of piglets to L-Ile supplementation under different dietary conditions. Four experiments were performed that started at 5 wk of age and lasted for 3 wk using individually-housed piglets. Unless indicated otherwise, diets were based on cereals and soybean meal and contained 1.0% standardized ileal digestible (SID) Lys. In Exp. 1, 4 diets were used in a 2×2 factorial design providing 50 or 60% SID Ile:Lys in combination with 57 or 70% SID Val:Lys. The Ile content of the diet did not affect performance. The ADFI and ADG were respectively 15 and 20% lower in piglets receiving diets with 57% SID Val:Lys compared with those receiving 70% SID Val:Lys. In Exp. 2, a control diet was formulated to provide 48% SID Ile:Lys. Four other diets were formulated by supplementing the basal diet with 1 of 2 sources of L-Ile differing in degree of purity to obtain 52 and 56% SID Ile:Lys in the diet. Level and source of L-Ile supplementation did not affect performance. To exclude a possible interaction between Ile and Lys, 4 diets were used in Exp. 3 in a 2x2 factorial design providing 1.00 or 1.15% SID Lys combined with 48 or 60% SID Ile:Lys. The ADG and F:G were affected by Lys supply (8 and 6% higher for piglets receiving 1.15% SID Lys) but not by Ile supply. Experiment 4 was carried out to test the effect of L-Ile supplementation using diets differing in BCAA content. Two protein sources (spray-dried blood cells and corn gluten meal) and 2 levels of Ile were used (50 and 65% SID Ile:Lys) in a 2x2 factorial arrangement. The SID Val:Lys and Leu:Lys contents were respectively 105 and 167% for diets containing spray-dried blood cells, and 70 and 180% for the diets containing corn gluten meal. Neither protein source nor Ile level affected performance in piglets. These studies indicated that the SID Ile:Lys requirement may not be greater than 50% in cereal-based diets.