A zoo-based, 11-year-old, uniparous southern black rhinoceros (Diceros bicornis minor) failed to conceive after weaning a calf. Behavioral observation and fecal progestagen monitoring confirmed irregular estrous cycles. Serial transrectal reproductive ultrasound examination revealed the cause to be recurrent anovulatory hemorrhagic follicles (AHFs). After four consecutive abnormal cycles dominated by AHFs, rational hormone therapy was implemented. Injectable prostaglandins, progesterone, estradiol, and a GnRH analog were given strategically to disrupt AHFs, boost normal estrus behavior, and promote ovulation. Oxytocin was added to the treatment regimen when transient accumulations of intraluminal uterine fluid consistent with endometritis were observed ultrasonographically. Oral diazepam was given judiciously for anxiolysis after the animal developed an aversion to injection. Treatment, which proceeded over eight cycles, was eventually associated with the restoration of normal behavioral estrus and ovulation. The rhinoceros conceived after natural mating and induced ovulation, delivering a healthy calf 490 days later, the longest reported gestation for the species.
Keywords: anovulatory hemorrhagic follicle; black rhinoceros; histrelin; infertility; long‐acting GnRH; long‐acting progesterone; oxytocin; prostaglandin; reproductive biology.
© 2025 Wiley Periodicals LLC.