Cardiopulmonary Parameters and Arterial Blood Gases During Etorphine-Medetomidine-Midazolam Immobilization in Free-Ranging Black Rhinoceroses (Diceros bicornis) Undergoing Electro-Ejaculation—A Preliminary Study

Abstract

Conservation management interventions for the critically endangered black rhinoceros (Diceros bicornis) require immobilization, which offer opportunities for semen collection and cryopreservation to establish genetic reservoirs. In free-ranging rhinoceroses, a combination of the potent opioid etorphine and the tranquilizer azaperone is routinely used for chemical immobilization but is associated with muscle rigidity and severe cardiopulmonary changes. Additionally, azaperone inhibits semen emission. Seven free-ranging, male, sexually mature black rhinoceroses were immobilized with an alternative protocol consisting of 4.5 mg etorphine, 5 mg medetomidine, 50 mg midazolam and 2,500 IU hyaluronidase delivered remotely by darting from a helicopter. During the immobilization, electro-ejaculation was performed with a portable electro-ejaculator, and a species-specific rectal probe. Animals were observed for muscle tremors. Longitudinal changes in respiratory rate, heart rate and peripheral oxyhemoglobin saturation, measured at 5 min intervals, were assessed using a general mixed model. Non-invasive oscillometric blood pressure and arterial blood gas variables were measured at first handling and before reversal and compared using the Wilcoxon rank sum test. All animals were successfully immobilized, showed no muscle tremors, presented with normal heart rates and lactate concentration (<5 mmol/L), recovered uneventfully, but experienced acidemia, hypoxemia and hypercapnia. Induction time and total time in recumbency were 4.2 ± 0.41 and 38.4 ± 6.9 min, respectively. Electro-stimulation commenced after 11.7 ± 3.98 min and completed after 24.3 ± 6.65 min. Semen-rich fractions were successfully collected from six animals. Our observations indicate that etorphine-medetomidine-midazolam provides a promising immobilization protocol for free-ranging black rhinoceroses, that allows for successful electro-ejaculation.

Arterial Blood Gases and Cardiorespiratory Parameters in Etorphine-Medetomidine-Midazolam Immobilized Free-Ranging and Game-Farmed Southern White Rhinoceroses (Ceratotherium simum simum) Undergoing Electro-Ejaculation

“…The lower body condition and better fitness of the free-ranging compared to the game-farmed rhinoceroses, may have improved ventilation ( 38 ). The generally lower PaCO 2 and higher pH in the rhinoceroses of all groups compared to previous reports in etorphine-azaperone immobilized white rhinoceroses ( 6 , 7 , 11 , 14 – 16 , 27 , 40 ) indicate that ventilation was better, despite an apparently lower f R. Similar results were previously obtained in black rhinoceroses immobilized with etorphine-medetomidine-midazolam ( 20 ). The absence of muscle tremors and an improved muscle relaxation induced by medetomidine and midazolam possibly resulted in a decreased chest wall rigidity, reduced global ventilation-to-perfusion mismatch and improved gas exchange through enhanced respiratory excursions ( 14 ).…”

“…Possibly, butorphanol alleviated this increase and the associated hypoxemia in animals of Groups 1 and 2 ( 6 ) and needs to be tested. However, lactic acidosis was absent in the rhinoceroses of all three groups as the concentrations remained within normal limits for the species ( 42 ), which we additionally observed in black rhinoceroses previously ( 20 ). These results may reflect the rapid and smooth induction achieved with the drug combination used ( 6 ), even in rhinoceroses darted from the helicopter.…”

“…All animals underwent electro-ejaculation (EE) by methods previously described elsewhere ( 32 ). The EE was performed with a portable, battery-powered electro-ejaculator (El Toro 3, Electronic Research Group, South Africa) and a specifically designed, custom-made rectal probe which the authors previously also applied in wild black rhinoceroses ( 20 ). Sets of stimuli, each consisting of 8–10 stimulations lasting 3 s, with a 2-s pause in between, were applied.…”

“…Hence, alternative immobilization protocols that allow for safe and effective semen collection via electro-ejaculation (EE) in rhinoceroses are required. Free-ranging black rhinoceroses undergoing EE were successfully immobilized with a combination of etorphine-medetomidine-midazolam ( 20 ). Specific α 2 -adrenoreceptor agonists, including medetomidine and detomidine, provide dose-dependent sedation, analgesia, muscle relaxation and anxiolysis ( 21 ) and have a sympatholytic effect, which may reduce stress- and etorphine-induced catecholamine release and associated side effects ( 21 ).…”