Effects of dietary branched-chain amino acid ratio on growth performance and serum amino acid pool of growing pigs

Branched-chain amino acids (BCAA), including leucine (Leu), isoleucine (Ile), and valine (Val), play key roles in protein metabolism. This study was conducted to investigate whether the dietary ratio of BCAA influences the growth performance and serum amino acid pool of the growing pigs. A total of 40 crossbred pigs (Large White x Landrace; 9.85 +/- 0.35 kg) were chosen and fed one of the five isocaloric diets varying in Leu:Ile:Val. The positive control diet contained 20% crude protein (CP) with a Leu: Ile: Val ratio of 1:0.51:0.63 according to the recommendation; for the other diets, the CP level was reduced to 17%, and the Leu:Ile: Val ratios were 1:1:1, 1:0.75:0.75, 1:0.51:0.63, and 1:0.25:0.25, respectively. The total BCAA amount was equal in all treatments, and the content of Leu, Ile, and Val was altered according to the setting ratios. No significant difference was observed in the growth performance between the pigs fed 20% CP and 17% CP diets supplemented with BCAA (P > 0.05). However, different Leu:Ile:Val ratios could affect the final weight (P < 0.05), average daily gain (ADG; P < 0.05), and feed: gain ratio (P = 0.06) of the pigs fed 17% CP diet. The final weight and ADG of the pigs in the 1:0.75:0.75 (17% CP), 1:0.51:0.63 (17% CP), and 1:0.51:0.63 (20% CP) groups were higher than those in the 1:0.25:0.25 (17% CP) group. The feed: gain ratio of the pigs fed the 1:0.75:0.75 (17% CP) diet was lower than that of those fed the 1:1:1 (17% CP) diet. There was no difference in the average feed intake among the treatments. Moreover, the diets supplemented with varied BCAA ratios influenced certain serum amino acid concentrations (P < 0.05), including Ile, Val, cysteine, and alpha-amino-adipic acid. These results indicated that a low CP diet (17%) supplemented with BCAA could keep up with the growth performance of growing pigs receiving adequate dietary protein (20%). The optimal Leu: Ile: Val within the range from 1:0.25:0.25 to 1:0.75:0.75 could improve the growth performance and serum amino acid profile of growing pigs fed the low CP diet.