Sedative and mechanical hypoalgesic effects of butorphanol in xylazine‐premedicated donkeys

REASONS FOR PERFORMING STUDY: Combinations of α2 -adrenoceptor and opioid agonists are commonly used in equids, but little scientific information is available on donkeys. OBJECTIVES: To compare the sedative and hypoalgesic effects of xylazine alone or in combination with different dosages of butorphanol in donkeys. STUDY DESIGN: Placebo-controlled, operator-blinded, randomised, crossover, Latin square study. METHODS: Six donkeys received intravenous normal saline and normal saline (NS-NS); xylazine (0.5 mg/kg bwt) and normal saline (X-NS); xylazine and 10 μg/kg bwt butorphanol (X-B10); xylazine and 20 μg/kg bwt butorphanol (X-B20); xylazine and 30 μg/kg bwt butorphanol (X-B30); and xylazine and 40 μg/kg bwt butorphanol (X-B40). Sedation scores (SS), head height above ground (HHAG) and mechanical nociceptive thresholds (MNT) were assessed before and for 120 min after treatment. Areas under the curve (AUC) values for 0-30, 30-60 and 60-120 min were computed for SS, HHAG and MNT. As appropriate, differences between treatments were analysed using the Friedman test followed by Dunn's test and a repeated measures one-way analysis of variance followed by Tukey's test; significance was set at P<0.05. RESULTS: All treatments apart from NS-NS induced sedation. Butorphanol treatments induced significantly larger SS-AUC0 -30 values than those for NS-NS (P<0.05). Compared to corresponding NS-NS values, HHAG-AUC0 -30 values were significantly smaller for all other treatments (P<0.001) and HHAG-AUC30-60 values were significantly smaller for X-B40 (P<0.05). Compared to NS-NS, all treatments induced mechanical hypoalgesia and yielded significantly larger MNT-AUC0-30 values (P<0.001). Treatment X-NS yielded significantly smaller MNT-AUC0 -30 values than those for X-B30 and X-B40 (P<0.05). Only MNT-AUC30 -60 values for X-B30 and X-B40 were significantly larger than those for NS-NS and X-NS (P<0.05). CONCLUSIONS: Sedation and mechanical hypoalgesia induced by xylazine were enhanced by butorphanol at 40 μg/kg bwt. This drug combination may be suitable for chemical restraint of donkeys undergoing certain clinical procedures.