Effects of dietary valine: lysine ratio on the performance, amino acid composition of tissues and mRNA expression of genes involved in branched-chain amino acid metabolism of weaned piglets

Objective: The goal of this study was to investigate the effects of dietary standard ileal digestible (SID) valine: lysine ratios on performance, intestinal morphology, amino acids of liver and muscle, plasma indices and mRNA expression of branched-chain amino acid (BCAA) metabolism enzymes. Methods: A total of 144 crossbred pigs (DurocxLandracexLarge White) weaned at 28 +/- 4 days of age (8.79 +/- 0.02 kg body weight) were randomly allotted to 1 of 4 diets formulated to provide SID valine: lysine ratios of 50%, 60%, 70%, or 80%. Each diet was fed to 6 pens of pigs with 6 pigs per pen (3 gilts and 3 barrows) for 28 days. Results: Average daily gain increased quadratically (p< 0.05), the villous height of the duodenum, jejunum and ileum increased linearly (p< 0.05) as the SID valine: lysine ratio increased. The concentrations of plasma a-keto isovaleric and valine increased linearly (p< 0.05), plasma aspartate, asparagine and cysteine decreased (p< 0.05) as the SID valine: lysine ratio increased. An increase in SID lysine: valine levels increased mRNA expression levels of mitochondrial BCAA transaminase and branched-chain a-keto acid dehydrogenase in the longissimus dorsi muscle (p< 0.05). Conclusion: Using a quadratic model, a SID valine: lysine ratio of 68% was shown to maximize the growth of weaned pigs which is slightly higher than the level recommended by the National Research Council [6].