Optimizing concentrations of dietary branched-chain amino acids (BCAA) can improve broiler chicken growth performance and carcass yields. A central composite design (CCD) study was conducted to understand the impact of dietary BCAA concentrations on Pectoralis major (PM) muscle protein expression and investigate the mechanisms behind how BCAA ratios affect broiler growth and muscle deposition. A total of 2,592 d-old Ross 344 × 708 male broilers were randomly placed in 144 floor pens. Each pen received 1 of 15 dietary treatments in the 23 CCD with 6 center points from 20 to 35 d of age, varying in digestible ratios of isoleucine:lysine (Ile:Lys; 52 to 75), valine:lysine (Val:Lys; 64 to 87), and leucine:lysine (Leu:Lys; 110 to 185). On d 35, 1 bird per pen was randomly selected for PM protein extraction and proteomic analysis via data independent acquisition protein sequencing with a timsTOF Pro 2 LC/MS/MS and Spectronaut 15 software. Branched-chain amino acid aminotransferase (BCAT1), adipocyte-type fatty acid-binding protein (FABP4), phosphoserine aminotransferase (PSAT1), O-N- acetylglucosamine transferase subunit p110 (OGT), and large neutral amino acids transporter small subunit 1 (SLC7A5) were identified, quantified, and analyzed as a CCD using the RSREG procedure of SAS ver. 9.4 with significance set at P ≤ 0.10. The surface response model for PSAT1 expression was significant (P = 0.0149; R2 = 0.24). However, the models for the other proteins were not significant (P ≥ 0.9592; R2 values ≤ 0.0336). A linear model effect (P = 0.0023) was observed for PSAT1 protein expression, while no quadratic (P ≥ 0.2085) or cross product (P ≥ 0.5886) regression effects were observed for any other proteins. A minimum stationary point was observed for BCAT1 protein. However, optimal values for the other proteins could not be obtained due to stationary saddle points. Still, the coefficients for the Ile:Lys cross-product ratio effect on PSAT1 (P = 0.0957) protein expression was significant.
Overall, the results indicate that varying concentrations of dietary BCAA may impact expression of proteins related to broiler skeletal muscle growth; however, further exploration will be required to explain the mechanisms behind how BCAA impact broiler growth and muscle development.