Effects of acepromazine and xylazine on subjective and objective assessments of forelimb lameness

BACKGROUND: To facilitate lameness evaluation, sedatives such as xylazine and acepromazine are regularly used in the clinical setting, despite concerns that they may confound lameness assessment. OBJECTIVES: The objective of this study was to determine the effect of low doses of acepromazine and xylazine on subjective and objective lameness assessment. STUDY DESIGN: Randomised, blinded, crossover study. METHODS: Six horses with experimentally induced solar pain were evaluated over a 1-hour period after treatment with intravenous xylazine (0.1 or 0.2 mg/kg), intravenous acepromazine (0.02 or 0.04 mg/kg), intravenous saline (1 mL) or local analgesia (4 mL 2% mepivacaine administered subcutaneously). Lameness was assessed objectively with inertial sensors and subjectively on a scale from 0 to 5. Lameness assessments were compared with logistic regression analysis to account for the repeated measures and cross-over study design (P < .05). RESULTS: Xylazine (0.1 and 0.2 mg/kg) or acepromazine (0.02 and 0.04 mg/kg) did not result in significant differences in objective lameness assessment (vector sum) or average subjective lameness grade. Local analgesia was associated with a decrease in subjective lameness grade (OR 0.32 [0.11-0.92], P = .03). Objective measures of lameness (vector sum) were significantly decreased 45 minutes (vector sum 41.8, P = .04) and 60 minutes (vector sum 47.3, P = .03) following local analgesia administration compared with baseline (vector sum 121.4). MAIN LIMITATIONS: Extrapolation of the experimental model of moderate lameness used in this study to broad range of clinical lameness situations should be performed carefully. CONCLUSIONS: These results support the use of low doses of xylazine or acepromazine to facilitate forelimb lameness evaluation up to 1 hour in duration.