Winner of Voorjaarsdagen Award 2014: Sedation and Mechanical Hypoalgesia Induced by Four Different Dosages of Butorphanol in Xylazine‐Premedicated Donkeys

Reasons for performing study Combinations of α 2 ‐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 ‐ B 10); xylazine and butorphanol 20 μg/kg bwt ( X ‐ B 20); xylazine and butorphanol 30 μg/kg bwt ( X ‐ B 30); and xylazine and butorphanol 40 μg/kg bwt ( X ‐ B 40). 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 ‐ AUC 0–30 values were not significantly different. The HHAG ‐ AUC 0–30 values for all treatments were smaller than corresponding values for S ‐ S (P<0.001). For HHAG ‐ AUC 30‐60, only X ‐ B 40 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 ‐ AUC 0–30 values (P<0.001). Treatment X ‐ S yielded significantly lower MNT ‐ AUC 0–30 values than those for X ‐ B 30 and X ‐ B 40 (P<0.05). Only MNT ‐ AUC 30–60 values for X ‐ B 30 and X ‐ B 40 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. Sources of funding:  Ross University School of Veterinary Medicine intramural grant. Competing interests:  None.