The ability to maintain bull white rhinoceros ( Ceratotherium simum simum ) in breeding groups while preventing unwanted reproduction could be beneficial for bull wellbeing compared to solitary housing. To date, no contraception has been investigated for male rhinoceros species, but anti-GnRH immunotherapeutics have been used in female white and greater one-horned rhinoceros, as well as other wildlife species, to reduce reproductive steroid hormone concentrations. This study investigated the efficacy of Improvest® in down-regulating testosterone concentrations in a genetically well-represented bull white rhinoceros. Improvest® (0.6 mg; Distributed by Zoetis, Inc., Kalamazoo, MI 49007) was administered in the left triceps muscle, followed by boosters at 4, 12, 26, 42, 51, and 67 weeks. Serum testosterone was measured by enzyme immunoassay in blood samples collected voluntarily approximately weekly before and during the initial treatment, then monthly for long-term monitoring. No adverse effects from Improvest® were observed with the exception of mild swelling at the injection site. A five-fold decrease in testosterone concentrations was measured within the fourth week after the second dose, 8 weeks following initial treatment, and basal concentrations (17.3 ± 1.1 ng/mL) were maintained until a break-through increase in concentrations occurred 16 weeks after a booster injection. This case study demonstrates that testosterone concentrations can be suppressed in white rhinoceros bulls treated with Improvest®. These findings suggest anti-GnRH immunotherapeutics could be promising tools for bull rhinoceros management, and further studies of consistency in responsiveness, effects on behavior and fertility, and reversibility are merited.
Hammond et al. (Wed,) studied this question.
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