Effect of environmental temperature on oxidative status, inflammatory response and endocannabinoid system at oestrus in dairy cows

Background: Heat stress (HS) poses a significant challenge to dairy production under climate change, as it compromises fertility, productivity and overall health in cows. This seasonal observational cross-sectional study investigated how environmental temperature affects oxidative status, inflammatory responses and endocannabinoid system (ECS) in dairy cows, comparing winter and summer conditions. Methods: Sixty Italian Holstein cows, 20 per farm, were enrolled from three farms in southern Italy. In winter and summer, temperature‒humidity index (THI) was recorded using data loggers and blood samples were collected from each cow’s coccygeal vein during oestrus. Serum samples were analysed to evaluate the oxidative status as reactive oxygen metabolites (d-ROMs) and biological antioxidant potential (BAP), inflammatory responses as tumour necrosis factor-alpha (TNF-α) and interleukin (IL)-10, and ECS as anandamide (AEA) and 2-arachidonoylglycerol (2-AG). Results: Temperature‒humidity index was significantly higher in summer than in winter (p < 0.001), confirming HS exposure. Anandamide levels showed no significant seasonal variation, while 2-AG concentrations were significantly reduced in summer compared to winter (p < 0.01). Oxidative stress increased in summer, with lower BAP (p < 0.05) and higher d-ROMs (p < 0.001). Tumour necrosis factor-alpha and IL-10 were significantly higher in summer than in winter (p < 0.001 and <0.05). Conclusion: The study demonstrates that summer HS could alter oxidative balance, stimulates inflammatory pathways and modulates ECS activity in dairy cows. Reduced 2-AG suggests potential ECS involvement in thermal-stress adaptation. These findings provide a foundation for future research on nutritional or management strategies aimed at improving resilience to HS.