Black rhinoceros ( Diceros bicornis spp.) are critically endangered species, with less than 65 individual animals housed in captivity within Association of Zoos and Aquariums-accredited zoos within the United States, and an estimated 5,500 individual animals of all subspecies surviving in the wild. Previously published reference values for circulating vitamin D3 (25OHD3; 55.7 ± 34.2 ng/ml) were based upon samples from free-ranging black rhinoceros in Africa. Recent research in human medicine has highlighted the importance of subclinical vitamin D deficiency, with links to increased risks for developing various health conditions. Serum samples collected opportunistically from two captive Eastern black rhinoceros ( Diceros bicornis michaeli) housed with seasonal access outdoors in a North American zoo were tested for 25-hydroxy-vitamin D (25OHD) levels over a 3-yr period. A commercially prepared pelleted diet containing vitamin D3 was fed to both rhinos. This study correlates environmental ultraviolet (UV) index, dietary supplementation, and seasonal serum 25OHD levels to compare with known 25OHD3 levels in free-ranging African black rhinoceros. Results in these two individuals suggest that D. bicornis spp. are dependent upon sunlight or UVB for measurable circulating 25OHD, and that current vitamin D3 supplementation levels may have little effect for Diceros spp. in human care housed in northern latitudes.
Keywords: 25-hydroxy-vitamin D; 25OHD; Black rhinoceros; UVB.