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

Combinations of α2 -adrenoceptor and opioid agonists are commonly used in equids, but little scientific information is available on donkeys.

To compare the sedative and hypoalgesic effects of xylazine alone or in combination with different dosages of butorphanol in donkeys.

Placebo-controlled, operator-blinded, randomised, crossover, Latin square study.

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.

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).

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.