Branched-chain amino acids in muscle growth: mechanisms, physiological functions, and applications.

Skeletal muscle accounts for approximately 40% of body mass and 50%-75% of whole-body protein, playing a central role in meat production and quality. Efficient protein synthesis in skeletal muscle relies on an adequate supply of nutrient substrates and a balanced amino acid profile. Branched-chain amino acids (BCAA), including leucine (Leu), isoleucine (Ile), and valine (Val), are the most abundant essential amino acids in skeletal muscle and contribute to both protein synthesis and oxidative energy production. Additionally, BCAA function as signaling molecules that regulate gene expression and protein phosphorylation cascades, which significantly influence physiological processes, such as protein synthesis and degradation, glucose and lipid metabolism, and cell apoptosis and autophagy. These processes are primarily mediated through the PI3K/AKT/AMPK/mTOR signaling pathways. This review summarizes BCAA transporters and catabolic metabolism, their role as signaling molecules in regulating protein metabolism and glucose and lipid equilibrium, and applications in animal production. These findings offer both theoretical insights and practical guidelines for the precise regulation of feed efficiency and production performance through tailored dietary BCAA supplementations.