AbstractBackgroundOvariohysterectomy (OHE) induces inflammation and stress in female dogs. The anti‐inflammatory effects of melatonin have been reported in several studies.ObjectivesThe goal of this study was to assess the effects of melatonin on the concentrations of melatonin, cortisol, serotonin, α‐1‐acid glycoprotein (AGP), serum amyloid A (SAA), c‐reactive protein (CRP), interleukin‐10 (IL‐10), interleukin‐8 (IL‐8), interleukin‐1β (IL‐1β) and tumour necrosis factor‐α (TNF‐α) before and after OHE.MethodsThe total number of animals was 25 and aligned in 5 groups. Fifteen dogs were divided into three groups (n= 5): melatonin, melatonin+anaesthesia and melatonin+OHE and received melatonin (0.3 mg/kg, p.o.) on days –1, 0, 1, 2 and 3. Ten dogs were assigned to the control and OHE groups (n= 5) without melatonin treatment. OHE and anaesthesia were performed on day 0. Blood samples were obtained via jugular vein on days –1, 1, 3 and 5.ResultsMelatonin and serotonin concentrations significantly increased in the melatonin, melatonin+OHE and melatonin+anaesthesia groups compared with the control group, while cortisol concentration decreased in the melatonin+OHE group compared with the OHE group. The concentrations of acute‐phase proteins (APPs) and inflammatory cytokines significantly increased after OHE. The CRP, SAA and IL‐10 concentrations decreased significantly in the melatonin+OHE group compared with the OHE group. The concentrations of cortisol, APPs and proinflammatory cytokines increased significantly in the melatonin+anaesthesia group compared with the melatonin group.ConclusionsThe oral administration of melatonin before and after OHE help controlling the high levels of inflammatory APPs, cytokines and cortisol induced by OHE in female dogs.