Sedation and mechanical hypoalgesia induced by four different dosages of butorphanol in xylazine-premedicated donkeys

Reasons for performing study:

Combinations of a2 - adrenoceptor and opioid agonists are commonly used in equines, but there is little scientific information on this topic in donkeys.

Objectives:

To compare the sedative and hypoalgesic effects of 4 dosages of butorphanol in xylazine-premedicated donkeys.

Study design:

In vivo experiment.

Methods:

Six donkeys received intravenous treatments: saline and saline (S-S); xylazine (0.5 mg/kg bwt) and saline (X-S); xylazine and butorphanol 10 μg/kg bwt (X-B10); xylazine and butorphanol 20 μg/kg bwt (X-B20); xylazine and butorphanol 30 μg/kg bwt (X-B30); and xylazine and butorphanol 40 μg/kg bwt (X-B40). Sedation score (0–3), head height above ground (HHAG), and mechanical nociceptive thresholds (MNT) of the left metacarpus were assessed before and for 120 min after treatment. Areas under the curve (AUC) for 0–30, 30–60 and 60–120 min post treatment were computed for sedation scores (SS-AUC), HHAG (HHAG-AUC) and MNT (MNT-AUC). Differences between treatments were analysed using the Friedman test followed by Dunn’s test and repeated measures one-way ANOVA followed by Tukey’s test.

Results:

All treatments except S-S induced sedation. Butorphanol treatments induced significantly greater SS-AUC0–30 values than those for S-S (P<0.05), but S-S and X-S SS-AUC0–30 values were not significantly different. The HHAG-AUC0–30 values for all treatments were smaller than corresponding values for S-S (P<0.001). For HHAG-AUC30-60, only X-B40 values were significantly smaller than corresponding values for S-S (P<0.05). Compared to S-S, all treatments increased MNT and yielded significantly higher MNT-AUC0–30 values (P<0.001). Treatment X-S yielded significantly lower MNTAUC0–30 values than those for X-B30 and X-B40 (P<0.05). Only MNT-AUC30–60 values for X-B30 and X-B40 were higher than those for S-S and X-S (P<0.05).

Conclusions:

Xylazine induced sedation and mechanical hypoalgesia that were enhanced by adding butorphanol at 40 μg/kg bwt. This drug combination may be suitable for chemical restraint of donkeys undergoing clinical procedures.

Ethical animal research:

The study was approved by the Ross University School of Veterinary Medicine Institutional Animal Care and Use Committee.