Development of a novel immobilisation protocol for black-faced impala ( Aepyceros melampus ssp. petersi) in Etosha National Park

Black-faced impala (Aepyceros melampus ssp. petersi) are endemic to Namibia where conservation management involves immobilisation and translocation, and mortality with current protocols is common. Critically evaluated field immobilisation protocols are needed to maximise animal safety. This prospective study was done in two phases: the first compared etorphine- and thiafentanil-based combinations, the second evaluated the influence of oxygen in impala receiving the thiafentanil-based combination. Animals (10 per group) received 50 mg ketamine (K) and 10 mg butorphanol (B), with either 2.0 mg etorphine (E) or 2.0 mg thiafentanil (T). A third group of ten impala were anaesthetised using TKB with supplemental nasal oxygen (O) at a rate of 5 L/minute. Behavioural, metabolic and physiological variables were assessed within five minutes of recumbency and at 10, 15, and 20 minutes post-recumbency. Statistical analyses for non-parametric data were performed to compare the treatment groups as well as time points; p = 0.05 considered significant. Following darting, 7/10 EKB animals were standing when approached, compared to 2/20 in the thiafentanil treatment groups. Time to first effect was significantly higher for EKB (155 +/- 105.7 seconds) compared to TKBO (61.5 +/- 21.4 seconds). Time to sternal after darting was significantly higher with EKB (411.6 +/- 174 seconds) compared to TKB (160.5 +/- 85.4 seconds) and TKBO (166 +/- 77.3 seconds). This study builds on previous work investigating the effects of potent opioids on impala and is the first evaluating their use in a field setting. The thiafentanil combination had a faster onset and resulted in a smoother induction than the etorphine combination. Additionally, oxygenation improved in animals receiving oxygen supplementation.