ROTH, Terri L.; Center for Conservation and Research of Endangered Wildlife, Cincinnati Zoo & Botanical Garden: The Role of Science in Breeding the Critically Endangered Sumatran Rhinoceros (Dicerorhinus sumatrensis)

The Sumatran rhinoceros is one of the most difficult mammals to breed in captivity. With a population of just three animals in the U.S. and virtually no existing information about the species’ reproductive physiology, a study commenced with the ultimate goal of producing offspring. Through serum hormone monitoring and ovarian ultrasound imaging, a database slowly was established and the mysteries of this species’ reproductive physiology unraveled. The most surprising finding was that the species is an induced ovulator, a trait uncharacteristic of other studied rhino species. Another perplexing discovery was that when the female was not mated, her anovulatory follicle often would luteinize resulting in unusual progesterone patterns and irregular cycle lengths. Over time, we determined that the female would be receptive to the male when her ovaries contained a 19-24 mm follicle, and serum progesterone concentrations were baseline (< 50 pg/ml). These findings were critical because pairing animals for mating when the female is not receptive often leads to aggression and injuries. Timed introductions based on scientific data resulted in successful matings and even pregnancy, but the study female experienced early embryo loss on five occasions. She was supplemented with the synthetic progestin, altrenogest, on her sixth pregnancy and successfully carried it to term delivering a healthy, male calf 475 days after mating. After this calf was weaned, ultrasound monitoring was again employed in an effort to breed the rhino a second time. After six consecutive matings, she finally conceived and carried the pregnancy to term (477 days), this time without the progesterone supplement. This is the first time in history that a Sumatran rhinoceros has produced two calves in captivity.