Abstract: Summer cow metritis is a major reproductive disorder in dairy farming,with its incidence and severity significantly increasing under high-temperature and high-humidity conditions. The disease is primarily caused by pathogenic microorganisms such as Fusobacterium spp.,Bacteroides spp.,Trueperella pyogenes and Escherichia coli,which proliferate more aggressively and invade the uterus under heat stress. The pathogenesis involves three key aspects：（1）exogenous infection,where pathogens directly invade through the open cervix during parturition;（2）endogenous infection,where metabolic disorders（e.g.,ketosis,ruminal acidosis）in the peripartum period compromise the intestinal barrier,allowing pathogens to migrate to the uterus via blood circulation;and（3）hormonal imbalance,where a sharp decline in postpartum estrogen levels suppresses immune function.Clinical manifestations include endometrial inflammation and purulent lochia discharge. The disease can be categorized into clinical endometritis （CE）and subclinical endometritis （SE）. While SE is asymptomatic,it poses greater harm,significantly reducing conception rates—some studies report a decline of over 50%. Epidemiological studies indicate that first-calving cows have a higher incidence than multiparous cows,with retained placenta,stillbirth,and dystocia being major contributing factors.In regions with hot and humid summers—such as Tianjin,southern Shaanxi,inland Shandong and Henan—heat stress reduces feed intak,weakens immunity,and promotes pathogen proliferation,leading to a higher incidence of metritis compared to other seasons. Prevention and control strategies should focus on environmental management,nutritional optimization and biosecurity measures.

Key words: metritis, herd management, Holstein cows, summer season