Methionine metabolism, functions, and application in swine.

Methionine (Met) is the only sulfur-containing essential amino acid for animals and is the second or third limiting amino acid in swine diets. It plays a role not only in protein synthesis, but also as an important methyl donor to participate in various biochemical reactions. Additionally, Met can be converted into several functional derivatives, such as S-adenosylmethionine (SAM) and homocysteine (Hcy) through which it exerts its biological functions. Specifically, appropriate supplementation with Met or SAM has been shown to provide a wide range of health-promoting effects, particularly in enhancing reproductive performance, improving intestinal morphology, regulating hepatic lipid metabolism, promoting muscle growth, and improving meat quality. In contrast, elevated Hcy levels can increase oxidative stress and inflammation, negatively affecting reproductive performance. Supplemental Met has been widely used in swine production for many years. This review summarizes recent advances in the application of Met and its derivatives in the pig industry, and explores their mechanism of action and optimal dosage as a feed additive, aiming to support the effective development and rational use of Met.