This study was conducted to evaluate the effects of N-Acetyl cysteine (NAC) supplementation on the productive and reproductive performance, antioxidant status and immune response in breeder quails reared under heat stress (HS). A total of 100 breeder quails were divided into four groups. One group was kept in an environmentally controlled room (22 °C) and considered as thermoneutral (TN) and three groups were kept at the 34 °C and fed with either a basal diet or the basal diet supplemented with 2.5 or 5 g/kg NAC. Heat stress decreased performance in birds fed the basal diet (P < 0.05) compared with the TN group. Higher feed intake (P < 0.05) and egg production (P < 0.05), improved feed efficiency (P < 0.05), haugh unit and hatchability variables (P < 0.05) occurred in NAC supplemented groups compared with the group reared under HS. Birds receiving NAC under HS had higher maternal serum IgG and egg yolk IgY indicating that the NAC in the diets improved the immune response of birds. Quails receiving the NAC diets exhibited higher (P < 0.05) plasma and liver activities of superoxide dismutase, catalase and glutathione peroxidase as well as lower (P < 0.05) plasma and liver levels of malondialdehyde compared with the HS group fed the basal diet. In addition, dietary supplementation with NAC increased (P < 0.05) the titers of antibodies for both primary and secondary injections in quails exposed to HS and elevated the antibody titer against SRBC to a level similar to that of quails under TN condition. Supplementation of the diet with NAC increased (P < 0.05) stimulation indices 24 and 36 h after the injection of phytohaemagglutinin compared with the basal group exposed to HS. All breeder quails receiving the NAC 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. All quails receiving NAC in the diet had lower (P < 0.05) plasma levels of triglycerides, total cho
