Branched-chain amino acids partially recover the reduced growth of pigs fed with protein-restricted diets through both central and peripheral factors

The objective of this study was to assess the growth efficiency of pigs fed with protein-restricted diets supplemented with branched-chain amino acids (BCAA) and limiting amino acids (LAA) above the recommended levels. Following 2 weeks of adaptation, 48 young barrows were weight matched and randomly assigned to 6 treatments (8 pigs/treatment) for 4 weeks: positive control (PC) with standard protein, negative control (NC) with very low protein containing LAA (i.e., Lys, Met, Thr and Trp) at recommended levels, and NC containing LAA 25% (L25), LAA 50% (L50), LAA+BCAA (i.e., Leu, Ile and Val) 25% (LB25) and LAA+BCAA 50% (LB50) more than recommendations. Feed intake (FI) and body weight (BW) were measured daily and weekly, respectively. At week 6, blood samples were collected, all pigs euthanized and tissue samples collected. The data were analyzed by univariate GLM or mixed procedure (SPSS) and the means were separated using paired Student's t-test followed by Benjamini-Hochberg correction. Relative to PC, NC had decreased FI, BW, unsupplemented plasma essential amino acids, serum insulin-like growth factor-I (IGF-I) and hypothalamic neuropeptide Y (NPY) (P < 0.01). Compared to NC, L25 or L50, LB50 had increased BW and serum IGF-I and decreased plasma serotonin and both LB25 and LB50 had higher FI, plasma BCAA, hypothalamic 5-hydroxytryptamine-receptor 2A and NPY and jejunal 5-hydroxytryptamine-receptor 7 (P < 0.01). Overall, supplementation of protein-restricted diets with increased levels of dietary BCAA partially recovered the negative effects of these diets on growth through improved IGF-I concentration and FI, which was associated with changed expression of serotonin receptors, blood AA and hypothalamic NPY.