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* INRA, UMR1079, F-35000 Rennes, France
,
Agrocampus Ouest, UMR1079, F-35000 Rennes, France
AJINOMOTO EUROLYSINE s.a.s, 75817 Paris Cedex 17, France
jaap.vanmilgen{at}rennes.inra.fr
Abstract
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 post-weaned piglets (12 to 25 kg) as Val is considered to be potentially limiting 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 levels (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 lower 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, 4 diets with 1.0% SID Lys were used in a 2x2 factorial design where 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 gain were respectively 15 and 20% lower 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 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 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 levels 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 
-ketoisovaleric acid, Ile and Leu concentrations after an overnight fast increased with increasing Val supply (P < 0.001). The results of these experiments indicate that the SID Val:Lys is at least 70%, which is slightly higher than the current NRC recommendation.
Key Words: branched-chain amino acids • feed intake • growth • pig • requirement • valine
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