Abstract:
With the rapid loss of individuals in the wild, semen cryopreservation has gained
importance to safeguard the genetic diversity of white rhinoceroses (Ceratotherium
simum). For semen collection via electro-ejaculation, immobilization of free-ranging
individuals requires the potent opioid etorphine, which is routinely combined with
azaperone, but causes hypoxemia, hypercarbia, acidemia, muscle rigidity, tachycardia,
and systemic hypertension. In this study, the suitability of two alternative immobilization
protocols including etorphine, medetomidine, and midazolam at different doses (high vs.
low etorphine) was evaluated in adult white rhinoceros bulls in two different management
systems (free-ranging vs. game-farmed) and undergoing electro-ejaculation. Fourteen
free-ranging (Group 1) and 28 game-farmed rhinoceroses (Group 2) were immobilized
with ≈2.5 µg/kg etorphine (high dose), ≈2.5 µg/kg medetomidine, ≈25 µg/kg
midazolam and 1,500–1,700 IU hyaluronidase and received ≈2.5 µg/kg of butorphanol
intravenously at first handling. Twenty game-farmed animals (Group 3) received ≈1 µg/kg
etorphine (low dose), ≈5 µg/kg medetomidine, ≈25 µg/kg midazolam and 1,700 IU
hyaluronidase. Respiratory rate, heart rate and peripheral hemoglobin oxygen saturation
(SpO2) were measured at 5-min intervals; non-invasive oscillometric blood pressures
and arterial blood gases at first handling and before reversal of the immobilization;
serum clinical chemistry analytes and hematocrit at first handling. Generalized mixed
models (fixed factors: group, time, recumbency; random factor: individual rhinoceros)
were applied to compare longitudinal changes between free-ranging and game-farmed rhinoceroses immobilized with the higher etorphine dose (Groups 1 and 2), and between
the two protocols tested in the game-farmed rhinoceroses (Groups 2 and 3). All
animals were successfully immobilized, presented with normal lactate concentrations
(<5 mmol/L), experienced no muscle tremors and recovered uneventfully. Hypoxemia
and hypertension persisted throughout the immobilization in all groups. Acidemia and
hypercarbia were absent in Group 1, but present in the game-farmed animals. The
lower etorphine dose in Group 3 resulted in significantly longer induction times, however,
tachycardia was not observed. SpO2 was higher for sternal vs. lateral recumbency.
Semen-rich fractions were recovered following electro-stimulation in 46 out of the
62 animals. Our findings suggest that etorphine-medetomidine-midazolam provides
effective immobilization with fewer side effects compared to previous reports in white
rhinoceroses and is suitable for successful electro-ejaculation.
