Effects of Dietary DL-Methionine Supplementation on Meat Quality and Antioxidant Capacity in Wenchang Chickens Subjected to Chronic Heat Stress

Heat stress adversely affects meat quality and antioxidant status in poultry, and nutritional interventions may help mitigate these effects. This study investigated the effects of dietary DL-methionine supplementation on meat quality, antioxidant capacity, and potential involvement of the Keap1–Nrf2–ARE signaling pathway in heat-stressed Wenchang chickens. A total of 480 healthy 81-day-old chickens were randomly assigned to four dietary treatments supplemented with 0.00%, 0.10%, 0.20%, or 0.40% DL-methionine and subjected to chronic heat stress conditions for 46 days. Dietary DL-methionine supplementation significantly affected meat quality and antioxidant status (p < 0.05). Compared with the other groups, supplementation with 0.20% DL-methionine resulted in increased cooked yield and reduced drip loss in both breast and thigh muscles. It also improved meat nutritional quality by increasing crude protein content, flavor-related amino acids, and polyunsaturated fatty acid proportions while decreasing saturated fatty acid levels. Furthermore, 0.20% DL-methionine increased the activities of superoxide dismutase, catalase, and glutathione peroxidase and reduced malondialdehyde content in breast muscle (p < 0.05). These changes were accompanied by altered expression of genes associated with the Keap1–Nrf2–ARE signaling pathway. Overall, dietary supplementation with 0.20% DL-methionine effectively improved meat quality and antioxidant capacity in Wenchang chickens under chronic heat stress conditions, whereas excessive supplementation (0.40%) showed less favorable effects.