This study was conducted to determine the effects of methionine (Met) supplementation on productive and reproductive performance, immune response and antioxidant status in breeder quails reared under heat stress (HS). A total of 125 breeder quails were divided into five groups. One group was kept in an environmentally controlled room at 22 ◦C and considered as thermoneutral, and four groups were kept at 34 ◦C and fed a basal diet (heat stressed) or a basal diet with Met concentrations 1.15, 1.30 and 1.45 times the quail requirements per NRC (1994) recommendations. HS decreased egg production in birds fed the basal diet (P <0.05). Higher feed intake (P <0.05), egg production (P <0.05), improved feed efficiency (P <0.05) and Haugh unit and hatchability variables (P <0.05) occurred in Met supplemented groups. Birds receiving Met under HS had higher maternal serum IgG, egg yolk IgY and offspring serum IgG (mg mL−1 ). Quails receiving the Met supplementation diets exhibited higher (P <0.05) plasma levels and liver activity of superoxide dismutase, catalase and glutathione peroxidase as well as lower (P <0.05) plasma and liver levels of malondialdehyde compared to the HS group fed the basal diet. All breeder quails receiving the Met supplement had lower (P <0.05) heterophil and H/L ratios as well as higher (P <0.05) lymphocytes than quails fed the basal diet under the same stress conditions. Our results suggest that dietary supplementation with Met could improve the performance, immunity and antioxidant status of quails by reducing the negative effects of HS.
