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.
Highlights
When immobilising drugs are developed for use in wild African ungulates, it is often difficult to make dose recommendations owing to the wide variety of species in this group and the lack of reported efficacy studies (Hernandez 2005)
Mean rectal temperatures of blesbok during the monitoring period varied between 39.0 oC and 39.2 oC (SE 0.08) with the etorphine treatment, and between 38.9 oC and 39.0 oC (SE 0.08) with the thiafentanil treatment
Mean rectal temperatures during etorphine immobilisation varied from 38.7 oC to 39.1 oC (SE 0.12) and with the thiafentanil treatment rectal temperatures varied from 38.8 oC to 39.2 oC (SE 0.12)
Summary
When immobilising drugs are developed for use in wild African ungulates, it is often difficult to make dose recommendations owing to the wide variety of species in this group and the lack of reported efficacy studies (Hernandez 2005). Impala are considered a difficult species to immobilise (Perrin et al 2015; Pfitzer et al 2019b; Zeiler & Meyer 2017a, 2017b) Their flighty nature and fine body structure can lead to physical injury when they are darted. Their physiological response to opioids seems unpredictable and frequent deaths have been reported (Meyer et al 2010; Perrin et al 2015; Zeiler & Meyer 2017a, 2017b).
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