Abstract:
Potent opioids are known to cause negative alterations to the physiology of immobilised
antelope. How these effects differ between species has not been studied. This study aimed to
compare time to recumbence and effects of opioid-based immobilisation on the physiology of
impala (Aepyceros melampus) and blesbok (Damaliscus pygargus phillipsi). Eight animals of each
species were immobilised, with 0.09 mg/kg etorphine and 0.09 mg/kg thiafentanil respectively,
in a randomised two-way cross-over study. Variables measured and analysed by means of a
linear mixed model included time to recumbence, heart rate, respiratory rate, arterial blood
pressure, blood gases, lactate and glucose. In blesbok, mean time to recumbence was not
significantly different with either drug (2.5 minutes and 2.2 min, respectively), but in impala
thiafentanil achieved a shorter time to recumbence (2.0 min) than etorphine (3.9 min). Mean
heart rates of immobilised impala were within reported physiological limits, but lower in
immobilised blesbok when both opioids were used (35 beats/min to 44 beats/min vs. 104 ± 1.4
beats/min resting heart rate). Impala developed severe respiratory compromise and
hypoxaemia from both opioids (overall mean PaO2 values ranged from 38 mmHg to 59 mmHg
over 30 min). In contrast, blesbok developed only moderate compromise. Therefore,
significantly different species-specific physiological responses to potent opioid drugs exist in
blesbok and impala. Given that these different responses are clinically relevant, extrapolation
of immobilising drug effects from one species of African ungulate to another is not
recommended.
