Bull access influences fecal progesterone metabolites in managed female white rhinoceros (Ceratotherium simum): Insights from hormonal and behavioral monitoring at The Wilds

Abstract

Refined husbandry has greatly improved reproduction in managed white rhinoceros, yet consistent breeding success remains a challenge. Social factors, particularly lack of mature bull access, are suggested contributors to reproductive challenges but supportive data is limited. At The Wilds, a large-landscape conservation center in Cumberland, Ohio, four postpartum multiparous and one nulliparous female white rhinoceros were monitored over a 10-month period. Fecal progesterone metabolite (fPM) assays and behavioral observations were conducted across three sequential conditions: indoor housing without a mature bull, pasture without a mature bull, and pasture with a mature bull. Baseline fPM values averaged 30 ± 1 ng/g in the postpartum, multiparous animals and 33 ± 3 ng/g in a nulliparous female. These values remained stable until a novel, mature bull was introduced, after which increases in fPM ranging from 131 to 174 ng/g, indicative of reproductive activity, were observed in four females following receptivity to mounting and copulation. A single smaller increase of 57 ng/g was recorded in the remaining female with limited reproductive behavior. Fecal testosterone metabolite analysis demonstrated that concentrations in the mature bull were significantly higher than those measured in the young males (<3 years old) present throughout all conditions, thereby confirming the juvenile status of the latter. The results of this study suggest that the introduction of a mature bull can stimulate reproductive activity in female white rhinoceros following a prolonged period of quiescence.