ABSTRACT
OBJECTIVE: To compare pain perception between gonadectomized and intact dogs. STUDY DESIGN: Blinded, prospective, cohort study. ANIMALS: A group of 74 client-owned dogs. METHODS: Dogs were divided into four groups: group 1-female/neutered (F/N), group 2-female/intact (F/I), group 3-male/neutered (M/N) and group 4-male/intact (M/I). Premedication consisted of intramuscularly administered acepromazine (0.05 mg kg-1) and morphine (0.2 mg kg-1), and subcutaneously administered carprofen (4 mg kg-1). Anaesthesia was induced with propofol (1 mg kg-1 intravenously and supplementary doses to effect) and maintained with isoflurane in 100% oxygen. Intraoperative analgesia was achieved with fentanyl infusion (0.1 µg kg-1 minute-1). Pain assessments [using the University of Melbourne Pain Scale (UMPS) and an algometer at the incision site (IS), parallel to the incision site (NIS), and on the contralateral healthy limb] were performed preoperatively, and at 1, 2, 4, 6, 9 and 20 hours after extubation. The time-standardised area under the curve (AUCst) for measurements was calculated and compared by performing a one-way multivariate analysis of variance (manova). Statistical significance was set at p < 0.05. RESULTS: Postoperatively, F/N exhibited higher pain than F/I, with estimated marginal means (95% confidence intervals) AUCstISGroup1 909 (672-1146) versus AUCstISGroup2 1385 (1094-1675) (p = 0.014), AUCstNISGroup1 1122 (823-1420) versus AUCstNISGroup2 1668 (1302-2033) (p = 0.024) and AUCstUMPSGroup1 5.30 (4.58-6.02) versus AUCstUMPSGroup2 4.1 (3.2-5.0) (p = 0.041). Similarly, M/N showed higher pain than M/I with AUCstISGroup3 686 (384-987) versus AUCstISGroup4 1107 (871-1345) (p = 0.031) and AUCstNISGroup3 856 (476-1235) versus AUCstNISGroup4 1407 (1109-1706) (p = 0.026), and AUCstUMPSGroup3 6.0 (5.1-6.9) versus AUCstUMPSGroup4 4.4 (3.7-5.2) (p = 0.008). CONCLUSIONS AND CLINICAL RELEVANCE: Gonadectomy affects pain sensitivity in dogs undergoing stifle surgery. Neutering status should be taken into consideration when planning individualized anaesthetic/analgesic protocols.