L-theanine improves meat quality in heat-stressed broilers via redox and mitochondrial modulation

This study evaluated the effects of L-theanine (L-Th) on growth performance, meat quality, muscle antioxidant capacity, and mitochondrial function in broilers under under heat stress (HS), aiming to provide a theoretical basis for its rational application. In total, 216 21–day-old AA broilers were allocated into 3 groups. The CON group was fed a basal diet at 22 ± 1 °C. The HS and HS + L-Th (600 mg/kg L-Th) groups were exposed to 33 ± 1 °C from 8:00 to18:00 daily, and 22 ± 1 °C otherwise. The trial period spanned 21 days. L-Th treatment significantly increased the body weight, average daily gain, pectoral muscle redness and glycogen content in heat-stressed broilers, while reducing the yellowness at 45 min, lightness at 24 h, and cooking loss (p < 0.05). Additionally, L-Th enhanced muscle antioxidant capacity, unregulated nuclear factor E2-related factor 2 (Nrf2) protein content, and increased the expression of the Nrf2 signalling pathway-related genes (p < 0.05). Furthermore, L-Th promoted the expression of genes associated with mitochondrial biosynthesis and energy metabolism, elevated the activities of citrate synthase and respiratory chain complexes (I, IV, and V), and consequently increased mitochondrial DNA copy number and ATP content in muscle (p < 0.05). In summary, L-Th alleviates HS-triggered oxidative damage by activating Nrf2 signalling pathway and enhancing mitochondrial biogenesis and function, thereby improving meat quality. This study provides an effective nutritional intervention strategy to combat heat stress in broiler, improving production performance and meat quality, and holds significant practical value.