Supplementation of methionine (Met) in broiler chicken diets is essential to support productive performance and optimise carcass yield. Met is the first limiting amino acid in corn and soybean-meal based diets for poultry. The DL-Met form is the main source used in broiler diets, but other sources such as acid free hydroxy-analogous methionine (HMA-FA) are available. Studies have indicated that the molar bioequivalence of HMA-FA is approximately 88% compared with DL-Met at 99% for growth traits. However, differences in absorption and metabolism between Met sources can influence their efficacy, especially when broilers are exposed to high temperatures. The substitution of DL-Met by HMA-FA is a potential strategy to mitigate the negative effects of heat stress because it is passively absorbed in the upper portion of the gastrointestinal tract. This review highlights the effects of substituting HMA-FA for DL-Met in diets for broiler chickens reared in different thermal environments.
