A comparative study of xylazine-induced mechanical hypoalgesia in donkeys and horses

Abstract

ObjectiveTo compare the effects of xylazine on mechanical nociceptive thresholds in donkeys and horses. Study designRandomized, controlled, crossover, Latin-square, operator-blinded design. AnimalsSix 3.1 ± 0.89 year old standard donkeys weighing 145.0 ± 30.5 kg and six 9.6 ± 4.4 year old Thoroughbred horses weighing 456.0 ± 69.0 kg. MethodsEach animal received one of four doses of xylazine (0.5, 0.7, 0.9, and 1.1 mg kg−1), or acepromazine (0.05 mg kg−1) or saline solution (0.9%) intravenously and mechanical nociceptive thresholds were assessed over 90 minutes. The areas under the threshold change versus time curve values for 60 minutes (AUC0-60) post-drug administration were used to compare the effect of treatment. A 1-week interval was allowed between successive trials on each animal. ResultsAll doses of xylazine, but not acepromazine or saline, increased mechanical thresholds for up to 60 minutes. Xylazine-induced hypoalgesia was dose-dependent and corresponding AUC0-60 values for each treatment were not significantly different between donkeys and horses (p≥ 0.0697). ConclusionThe hypoalgesic effects of xylazine at four different doses were not different between donkeys and horses. Clinical relevanceXylazine induced a similar degree of mechanical hypoalgesia in donkeys and horses suggesting that similar doses are needed for both species with regard to analgesia.