Metabolomic Profiles Associated With Difference in Muscle Protein Degradation Between Fast‐ and Slow‐Growing Chicks During the Neonatal Period

We aimed to identify metabolites and metabolic pathways involved in differences in muscle protein degradation in broiler chicks during the neonatal period. To this end, we performed gas chromatography-mass spectrometry-based metabolomic analyses of plasma, pectoralis major muscle, and liver samples. Based on body weight gain from 1 to 5 days of age, 5-day-old broiler chicks (Ross308) were divided into three groups (slow-, intermediate-, and fast-growing groups). First, we confirmed that muscle protein degradation levels were closely associated with body weight gain. Untargeted metabolomic analysis revealed that 4, 14, and 22 metabolites in plasma, muscle, and liver, respectively, were correlated with the body weight gain of chicks from 1 to 5 days of age (Pearson's correlation, |r| ≥ 0.4). Most metabolic pathways identified in plasma and muscle were involved in either protein or amino acid metabolism, while those in liver were related to tricarboxylic acid cycle and carbohydrate metabolism. Interestingly, the expression of genes encoding enzymes related to branched-chain amino acid (BCAA) catabolism were higher in the slow-growing chicks than in the fast-growing ones. These results suggest that BCAA catabolism is important for muscle protein degradation levels and body growth of broiler chicks during the neonatal period.