Beyond Protein Synthesis: The Multifunctional Role of Functional Amino Acids in Modulating Meat Quality in Ruminants

ABSTRACT Meat quality is a critical economic trait in ruminant production because it directly influences consumer acceptability, market value, and the long‐term sustainability of the livestock industry. Amino acids (AAs) have traditionally been regarded primarily as substrates for protein synthesis. However, growing evidence indicates that they also regulate multiple aspects of meat quality. Given the increasing demand for high‐quality ruminant meat and the growing interest in nutritional regulation of carcass traits, this review synthesizes current evidence on how functional amino acids (FAAs) modulate meat quality in ruminants, including cattle, sheep, and goats. We first summarize the core indicators of meat quality—including color, water‐holding capacity, tenderness, marbling, and flavor—and the current understanding of how these attributes are regulated by AA metabolism. We then review the specific effects and underlying mechanisms of key FAAs and their derivatives in ruminants: Lysine improves carcass leanness and nitrogen utilization efficiency; methionine enhances antioxidant capacity and exerts programming effects on fetal development; tryptophan regulates stress responses and digestive physiology via neuroendocrine pathways; branched‐chain amino acids (BCAAs) activate the mTOR signaling pathway and promote muscle protein synthesis; glutamate and glutamine support intestinal health, immunity, and reproductive performance; arginine and its derivatives (citrulline, guanidinoacetic acid, and N‐carbamoylglutamate) regulate vasodilation, energy metabolism, and endogenous arginine synthesis; and other functional AAs (glycine, serine, β‐alanine, histidine, betaine, and taurine) contribute to collagen stability, methyl‐group metabolism, meat color stability, and antioxidant defense. We further discuss strategies for practical application, including rumen‐protected delivery technologies, utilization of sustainable forage resources, and systematic evaluation of AA requirements for precision supplementation. Collectively, this review highlights the mechanisms through which FAAs regulate meat quality and identifies key research gaps and future directions in this field. The synthesized evidence provides a theoretical basis for developing nutritional strategies that simultaneously improve meat quality, production efficiency, and environmental sustainability in ruminant production systems.