Do potent immobilising-opioids induce different physiological effects in impala and blesbok?

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 PaO 2 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.

Evaluation of two different etorphine doses combined with azaperone in blesbok (Damaliscus pygargus phillipsi) immobilisation

“…Keeping induction time as short as possible is desirable when capturing antelope because this is believed to translate into a reduction in capture-related morbidity (Meyer et al 2008a ; Meyer et al 2008b ). Under field conditions, a short induction time also reduces the risks of animals being attacked by predators and other herd members (Pfitzer et al 2020 ). In this study, the reduced etorphine dose did not prolong the induction time.…”

“…It has been reported that opioids, either used as a sole agent or in combination with other drugs, can lead to hypertension in wild herbivores (Buss et al 2016 ; Gaudio et al 2020b ; Hattingh et al 1994 ; Heard et al 1996 ; Pfitzer et al 2020 ). The mechanisms behind this are not yet completely clear, but one hypothesis is that hypertension might be induced by a sympathetic nervous system (SNS) reflex response to the drug-induced hypoxia and hypercapnia.…”

“…Sample size calculation was performed by power analysis using the means and standard deviations of the paired differences of cardiorespiratory variables (i.e. PaO 2 , PaCO 2 and A-a gradient) from previous research (Pfitzer et al 2020 ) with an α = 0.05 and power = 0.8. For all data, median (range) (scores) or mean ± standard deviation (s.d.)…”