Sodium selenite attenuates Tg-induced apoptosis and ER stress in mouse granulosa cells. Cells were treated with Tg (500 nM) in the absence or presence of sodium selenite (5 ng/mL) at 37 °C for 24 h, and then processed for cell viability and apoptosis analysis by CCK-8 kit (A) and flow cytometry (B, C), respectively. Caspase 3 Activity of the MGCs is measured by a colorimetric assay kit (D). Western blotting (E) was used to analyze the protein expression of BAX (F), GRP78 (G), and CHOP (H). β-actin was used to normalize the protein expression levels. The statistical analysis results are shown as bar graphs. The data are represented as the mean ± SEM of three independent experiments, and each independent experiment includes three technical replicates. Bars with different lowercase letters are significantly different (p < 0.05).