Cardiopulmonary effects of ketamine-butorphanol-medetomidine and etorphine-azaperone drug combinations used to immobilise zebra (Equus zebra)

Abstract

Objective To compare immobilisation efficacy of a non-potent opioid drug combination to the preferred etorphine-azaperone combination in zebras. Study design Prospective, randomised crossover trial. Animal population Ten adult zebras. Methods Each zebra was immobilised, by darting, twice using two different combinations: ketamine-butorphanol-medetomidine (KBM; 7 ml dart) and etorphine-azaperone (EA; 1 ml dart) in random order, three weeks apart. A stopwatch was started once the dart was placed to record times to recumbency and standing during induction and recovery, respectively. Once the zebra were recumbent and instrumented, physiological parameters were measured and recorded, at 5-minute intervals until 20 minutes. The quality of immobilisation was scored subjectively using muscle relaxation, palpebral reflexes and movement as indicators. Antagonist drugs were administered for recovery 5 minutes after the last recordings. Combination KBM was antagonised using atipamezole at 7.5 mg mg-1 medetomidine dose (half intravenous then half intramuscular) and intravenous naltrexone at 2 mg mg-1 butorphanol dose. Combination EA was antagonised using intravenous naltrexone at 20 mg mg-1 etorphine dose. Physiological parameters were compared between combinations using a general linear mixed model. Data reported as mean (range) unless otherwise stated. The drug and dart cost of immobilisation were compared descriptively. Results The mean dose of ketamine-butorphanol-medetomidine were 3.30 (3.04 to 3.57), 0.40 (0.38 to 0.42) and 0.16 (0.15 to 0.17) mg kg-1; and etorphine-azaperone were 0.02 (0.02) and 0.20 (0.18 to 0.22) mg kg-1, respectively. KBM and EA induced recumbency in a median (range) of 420 (300 to 600) and 240 (180 to 300) seconds, respectively. Zebras remained recumbent throughout the study procedures. Systolic blood pressures were 225 (136 to 286) and 167 (93 to 268) mmHg and PaO2 were 64 (46 to 90) and 47 (20 to 85) mmHg for KBM and EA, respectively. Median (range) time to standing, after administering antagonists was 90 (18 to 2 220) and 26 (7 to 72) seconds for KBM and EA, respectively. It costed R 5 842.00 to immobilise and antagonise a zebra using KBM which was six-and-a-half times more expensive than EA (R 897.00). Conclusions and clinical relevance The non-potent opioid KBM combination may provide a reliable alternative to the preferred EA combination for the immobilisation of zebras, especially in captive conditions. The superior muscle relaxation and apparent deeper plane of anaesthesia achieved with KBM could make this combination a good alternative to immobilise zebra that require painful procedures. Systemic hypertension and moderate hypoxaemia are clinical concerns when using KBM and EA, respectively. With the currently available preparations, the high costs associated with KBM, and the larger dart required for its administration, may limit its field use. Further evaluation of the KBM combination’s efficacy in free-ranging zebras is required.