The standardized ileal digestible valine-to-lysine requirement ratio is at least seventy percent in postweaned piglets

To reduce the impact of animal production on the environment, the CP content of the diet can be reduced by limiting the excess supply of AA. Improving the balance between AA relative to the requirement of the animal implies that we need to have accurate knowledge of the requirement of individual AA. The purpose of this study was to determine the Val requirement in postweaned piglets (12 to 25 kg) because Val is considered to be potentially limiting to performance after Lys, Met (and Cys), Thr, and Trp. The first experiment was carried out to identify a diet limiting in Lys supply. In this experiment, piglets were offered 1 of 3 diets: a low-CP diet containing low or adequate Lys concentrations [providing 1.0 and 1.2% standardized ileal digestible (SID) Lys, respectively] or a normal-CP diet with 1.2% SID Lys. Average daily gain of piglets receiving the diet containing 1.0% SID Lys was significantly less than that of piglets receiving diets containing 1.2% SID Lys at low or normal CP (486 vs. 522 g/d, respectively; P < 0.01). In Exp. 2, four diets with 1.0% SID Lys were used in a 2 x 2 factorial design, in which diets contained 57 or 70% SID Val: Lys in combination with 50 or 60% SID Ile: Lys. Independent of the Ile supply, feed intake and daily BW gain were, respectively, 15 and 20% less in piglets receiving diets providing 57% SID Val: Lys compared with piglets receiving 70% SID Val: Lys (P < 0.001). The Ile content of the diet did not affect feed intake or daily BW gain (P > 0.10). Experiment 3 was conducted to evaluate the response of piglets to an increasing Val supply provided by 2 sources of L-Val differing in the degree of purity. Increasing the Val supply from 58 to 66% SID Val: Lys resulted in a linear increase in both feed intake and daily gain by 24 and 30%, respectively (P < 0.001). No difference was observed between both sources of L-Val (P > 0.10). Experiment 4 was a dose-response study using 5 concentrations of Val supply (ranging from 60 to 80% SID Val: Lys). The estimated SID Val: Lys requirements for maximizing ADFI, ADG, and G: F were, respectively, 74, 70, and 68% using a linear-plateau model, and 81, 75, and 72% using a curvilinear-plateau model. Plasma Val, plasma alpha-ketoisovaleric acid, Ile, and Leu concentrations after an overnight fast increased with increasing Val supply (P < 0.001). The results of these experiments indicated that the SID Val: Lys was at least 70%, which was slightly greater than the current NRC recommendation.