Vitamin D status in North American managed black rhinoceros (Diceros bicornis) and white rhinoceros (Ceratotherium simum).

Black rhinoceros (Diceros bicornis) and white rhinoceros (Ceratotherium simum) in managed care experience environmental conditions that differ from those in the wild, including potential variation in exposure to ultraviolet B radiation, which may influence vitamin D status. In other species, vitamin D insufficiency has been linked to skeletal, muscular, and reproductive disorders, but information on vitamin D in managed rhinoceros remains limited. In this study, liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to quantify serum 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 (25OHD2 and 25OHD3, respectively) concentrations in black and white rhinoceroses housed at North American institutions. Data were evaluated for potential differences in vitamin D associated with species, sex, age, season, location, and female reproductive status. 25OHD2 was undetectable in more than 50% of white rhinoceros samples and 80% of black rhinoceros samples. Conversely, 25OHD3 concentrations varied significantly with season and location (P < 0.05), with higher concentrations during summer months and in regions of greater solar irradiance. No relationships were identified between 25OHD3 concentrations and species, sex, age, or reproductive status. These findings provide the first vitamin D reference data for managed white rhinoceros and expand available information for black rhinoceroses. Together, the results suggest that environmental factors such as sunlight exposure have a greater influence on circulating vitamin D than demographic characteristics, providing a foundation for further investigation into how management conditions impact vitamin D metabolism and associated health in managed rhinoceroses.