Actavia 0 Xiong, Yongjie Yin, Qirun Song, Kai Li, Jing He, Shaojun 2021 2021-4-30 179-187 Alpha lipoic acid (ALA), a natural lipophilic compound, plays an important role in regulating several metabolic pathways due to its antioxidant properties. This study aims to investigate whether ALA could be used as a feed additive to enhance the antioxidant capacity of the ovary tissue in hens exposed to heat stress (HS). One hundred and sixty 128-days-old female chickens were randomly assigned into four groups: the control group (Con), ALA treatment group (ALA), ALA and HS treatment group (ALA + HS), and HS treatment group (HS). The ALA and ALA + HS groups were fed a basal diet with 0.25% ALA, whereas the Con and HS groups were fed a basal diet only. Serum oestradiol, progesterone levels, biomarkers of antioxidant capacity, and endoplasmic reticulum (ER) stress markers were detected in the ovaries of heat-stressed chickens. HS decreased serum oestradiol and progesterone concentrations compared with the control group, whereas dietary ALA (0.25%) increased oestradiol and progesterone levels in the serum of heat-stressed hens. Malondialdehyde concentration in the ovary was higher in the HS group than that of the ALA + HS group. Compared with the HS group, ALA increased the enzymatic activities of superoxide dismutase, glutathione peroxidase, and catalase in the ovaries of ALA + HS group. Simultaneously, ALA enhanced the total antioxidative capacity of the ovaries of heat-stressed hens. Moreover, ALA also significantly inhibited the increased expression of glucose-regulated protein 78 and CCAAT/enhancer-binding protein homologous protein, which are two markers of ER stress, and heat shock protein 70, a key biomarker of heat stress, in the ovaries of the ALA + HS group as compared to those of the HS group. This work implied that dietary ALA supplementation improved the antioxidant capacity and attenuated the HS-induced reduction of serum oestradiol and progesterone levels and modulated the oxidative and ER stress, which are involved in the protective effect of ALA in hens exposed to hyperthermia. 5 66