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 4.5mg etorphine, 5mg medetomidine,
50mg 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 5min 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 ± 6.9min, respectively. Electro-stimulation commenced after
11.7 ± 3.98min and completed after 24.3 ± 6.65min. Semen-rich fractions were successfully collected from six animals. Our observations indicate that etorphinemedetomidine-
midazolam provides a promising immobilization protocol for free-ranging
black rhinoceroses, that allows for successful electro-ejaculation.
