Comparison of thiafentanil-medetomidine to etorphine-medetomidine immobilisation of impalas (<i>Aepyceros melampus</i>)

Abstract

Impalas (Aepyceros melampus) are increasingly valuable in the South African wildlife industry, and there is a greater need to chemically immobilise them, ideally with minimal risk. This study aimed to compare the times to recumbency and physiological effects of thiafentanil-medetomidine versus etorphine-medetomidine immobilisation. A combination of thiafentanil (2 mg) + medetomidine (2.2 mg) and etorphine (2 mg) + medetomidine (2.2 mg) was administered (to nine impalas; crossover design) via a dart. After darting, a stopwatch was started to record times to recumbency (time from darting until recumbent without attempts to stand). If apnoea was present, the impalas received one or more boluses of butorphanol (1:1 potent opioid dose). Data collection included arterial blood gas analysis and the number of butorphanol boluses. Two-sample t-tests were used to compare differences between combinations. The time to recumbency for thiafentanil-medetomidine was 12.2 (± 6.8) min and no different from 14.5 (± 5.2) min for etorphine-medetomidine (p = 0.426). The thiafentanil-medetomidine combination required more butorphanol boluses (median: 2; interquartile range: 2–3) compared to etorphine-medetomidine (median: 0; interquartile range: 0–1) (p = 0.001). Despite butorphanol treatment and resolution of apnoea, all impalas suffered hypoxaemia (PaO2 ± 44.0 mmHg). Thiafentanil-medetomidine did not immobilise impalas more rapidly than etorphine-medetomidine, and resulted in more apnoea that required rescue butorphanol boluses. Marked hypoxaemia resulted from both combinations, mainly because of right-to-left intrapulmonary shunting and not because of hypoventilation. Butorphanol and oxygen supplementation should be considered as essential rescue interventions for all impalas immobilised with these potent opioid combinations.

Efficacy and Animal Welfare Impacts of Novel Capture Methods for Two Species of Invasive Wild Mammals in New Zealand

“…Many of these animal welfare risks can be mitigated using highly potent and fast-acting pharmacological agents. Thiafentanil (often used in combinations) has become an increasingly popular sedative for remote chemical immobilisation of wildlife [31,32,[50][51][52][53]. The IT recorded with the use of thiafentanil (mean of 3 min) were short when compared to deer helicopter darting methods using non-opioid pharmacological regimens.…”

Etorphine-Azaperone Immobilisation for Translocation of Free-Ranging Masai Giraffes (Giraffa Camelopardalis Tippelskirchi): A Pilot Study

“…where FiO 2 is the fraction of inspired oxygen (21% for room air), Pb is the barometric pressure measured during the study by the blood gas analyser, PH 2 O is the partial pressure of vapor in the alveoli (47 mmHg), PaCO 2 is the partial pressure of carbon dioxide measured by the BGA, and RQ is the respiratory quotient, dependent on metabolic activity and diet, and is considered to be 1.0 for ruminants [24]. Since the capture site was not at sea level, we calculated the PaO2 expected for the average altitude we worked at (i.e., 1884 m) in order to use it as the cut-off value for defining hypoxaemia, using the alveolar-to-arterial oxygen tension formula.…”

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

“…The species most commonly used for this purpose is the impala. Impalas are easily kept in zoo as they are, not classified as threatened and are readily available in the wild and in intensive farming operations in Southern Africa (Harthoorn 1967 ; Janssen et al 1993 ; Meyer et al 2008 ; Perrin et al 2015 ; Pfitzer et al 2019b ; Zeiler & Meyer 2017a , 2017b ). Looking at the phylogenetic tree of the subfamily of Antilopinae, impala are somewhat removed from other subfamilies commonly captured by immobilisation such as Hippotraginae, which include sable antelope ( Hippotragus niger ), roan antelope ( Hippotragus equinus ) and oryx ( Oryx gazella ); and Alcelaphinae, which include blesbok, two wildebeest species ( Connochaetes spp.…”

“…(Chen et al 2019 ; Hernandez Fernandez & Vrba 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 flighty nature and fine body structure can lead to physical injury when they are darted. Furthermore, 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 ). Accordingly, the physiological response of impala to opioids might not necessarily be representative and comparable to many other antelope species.…”