Abstract:
Etorphine–azaperone is the most commonly used drug combination for chemical
immobilisation of free-ranging white rhinoceroses, but causes several profound physiological
disturbances, including muscle tremors. The addition of benzodiazepine sedatives, such as
midazolam, has been proposed to reduce the muscular rigidity and tremors in immobilised
rhinoceroses. Twenty-three free-ranging, sub-adult white rhinoceros bulls were darted and
captured using a combination of etorphine plus either azaperone or midazolam. Skeletal
muscle tremors were visually evaluated and scored by an experienced veterinarian, and
tremor scores and distance run were compared between groups using the Wilcoxon rank
sum test. No statistical differences were observed in tremor scores (p = 0.435) or distance run
(p = 0.711) between the two groups, and no correlation between these variables was detected
(r = –0.628; p = 0.807). Etorphine–midazolam was as effective as etorphine–azaperone at
immobilising rhinoceroses, with animals running similar distances. Although the addition of
midazolam to the etorphine did not reduce tremor scores compared to azaperone, it might
have other beneficial immobilising effects in rhinoceroses, and further investigation is
necessary to elucidate possible methods of reducing muscle tremoring during chemical
immobilisation of rhinoceroses.
