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 thiafentanilmedetomidine
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 thiafentanilmedetomidine
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.
