48 Effects of dietary isoleucine and valine supplementation to excess or low leucine diets on nitrogen balance and metabolism of branched-chained amino acids in growing pigs

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Abstract An experiment was conducted to test the hypothesis that Ile and Val supplementation may overcome detrimental effects of excess dietary Leu on N balance and metabolism of branched-chained AA (BCAA) in growing pigs. A total of 144 barrows (28.5 ± 2.5 kg) were housed in metabolism crates and randomly assigned to 18 diets. The basal diet contained 0.98% standardized ileal digestible (SID) Lys and had SID Leu, Val, and Ile ratios to SID Lys of 100, 60, and 43%, respectively. Two levels of synthetic L-Leu (0 or 2.0%), 3 levels of synthetic L-Ile (0, 0.1, or 0.2%), and 3 levels of synthetic L-Val (0, 0.1, or 0.2%) were added to the basal diet for a total of 18 diets in a 2 × 3 × 3 factorial. Urine and fecal samples were collected for 5 d after 7 d of adaptation. Blood, skeletal muscle, and liver samples were collected at the conclusion of the experiment. Data were analyzed as a 2 × 3 × 3 factorial using the PROC MIXED of SAS with concentrations of Leu, Val, and Ile, and all interactions as main effects and replicate as random effect. No interactions among main effects were observed, but excess Leu in diets reduced (P < 0.05) N retention and biological value of diets and increased (P < 0.05) plasma urea N (PUN). However, PUN was reduced (P < 0.05) as dietary Val increased. Concentrations of BCAA in liver were greater (P < 0.05) in pigs fed excess-Leu diets than in pigs fed low-Leu diets, but concentrations of BCAA in muscle were greater (P < 0.05) in pigs fed low-Leu diets. In conclusion, excess dietary Leu reduced N retention and biological value of diets and increased PUN in growing pigs, but Val supplementation may help overcome negative effects of excess Leu.