摘要Background Rises in global warming and extreme weather occurrence make the risk of heat stress(HS)induced by high ambient temperatures more likely in high-yielding dairy cows,resulting in low milk quality and yield.In ani-mals,oxygen is involved in many physiological and metabolic processes,but the effects of HS on oxygen metabolism remain unclear.Thus,the current study aimed to investigate how oxygen metabolism plays a role in health status of dairy cows by measuring the milk yield,milk composition,and blood biochemical variables of cows under different levels of HS:none(No-HS),mild(Mild-HS),and moderate HS(Mod-HS).Results The HS significantly increased rectal temperature(Ptreat＜0.01)and respiration rate(Ptreat＜0.01).Under Mod-HS,greater Na+(P＜0.05)and lower total CO2,and pH(P＜0.05)were observed relative to those under No-HS and Mild-HS.Oxygen concentrations in both coccygeal artery and mammary vein(Ptreat＜0.01)were lower under Mod-HS than under No-HS.Coccygeal vein concentrations of heat shock protein 90(HSP90)(P＜0.05)increased during Mod-HS compared with those in cows under No-HS.Malondialdehyde increased during Mod-HS,and glu-tathione peroxidase(P＜0.01)increased during Mild-HS.Coccygeal vein concentrations of vascular endothelial growth factor(P＜0.01),heme oxygenase-1(P＜0.01),and hypoxia-inducible factor 1α(P＜0.01)were greater in cows under Mod-HS than those under No-HS.Red blood cell count(P＜0.01)and hemoglobin concentration(P＜0.01)were lower in the coccygeal vein of dairy cows under Mild-and Mod-HS than those of cows under No-HS.Conclusions Exposure to HS negatively impacts the health status and lactation performance of dairy cows by limit-ing oxygen metabolism and transportation.However,the specific mechanism by which HS affects mammary function in cows remains unclear and requires further exploration.