The Role of Branched-Chain Amino Acids in Nutrient Allocation of the Porcine Placenta: A Review

During swine gestation, the placenta serves as the sole interface for nutrient, gas, and signaling molecule exchange between the dam and fetuses, and its function critically determines pregnancy outcomes. Branched-chain amino acids (BCAAs)—leucine, isoleucine, and valine—are substrates for protein synthesis, precursors for glutamate and glutathione, and signaling molecules that activate the mechanistic target of rapamycin (mTOR) pathway. This review synthesizes current evidence on BCAA transport, catabolism, and signaling in the porcine placenta, organized around four mechanistic axes: transporter-mediated transplacental transfer, local catabolism supporting energy production and antioxidant defense, mTORC1-dependent regulation of growth and differentiation, and modulation of endocrine and immune homeostasis. Both deficiency and excess of BCAAs compromise placental function, contributing to intrauterine growth restriction and metabolic programming abnormalities through a U-shaped dose–response relationship. Critical knowledge gaps remain, including the reliance on rodent and in vitro models, the absence of standardized supplementation protocols and dose–response data, unaddressed confounders (parity, litter size, environment), and the lack of formal power analyses or meta-analytic synthesis. We propose precision dietary strategies to optimize BCAA supplementation during gestation for improved reproductive performance in swine.