LC-MS/MS Reveals Vitamin D Levels in Zoo Rhinos

Black rhinoceros (Diceros bicornis) and white rhinoceros (Ceratotherium simum) living in zoos or other managed care settings experience a different environment than they would in the wild, including possibly getting less exposure to UVB rays from the sun, which can affect how much vitamin D their bodies make. In other animal species, not having enough vitamin D has been tied to problems with bones, muscles, and reproduction, but we still don't know very much about how vitamin D levels look in rhinos living under human care. Hoping to bridge this gap, researchers at the Cincinnati Zoo & Botanical Garden, used liquid chromatography-tandem mass spectrometry (LC-MS/MS) to check vitamin D levels in black and white rhinos living at zoos across North America. Specifically, they measured two related forms of vitamin D, known as 25OHD2 and 25OHD3, in the rhinos' blood samples. Their findings were published in the journal Conservation Physiology.¹

Why is Vitamin D Exposure So Hard to Replicate for Animals like Rhinos in Zoo Settings, and What Might That Mean for Their Health?

Conservation research and animal care programs have come a long way in giving animals what they need in captivity. Diets are now put together to meet each animal's nutritional needs, enclosures are designed to encourage natural behaviors specific to each species, and preventive healthcare keeps getting better.^2-5Even with all this progress, some parts of an animal's natural habitat, like the exact weather and environmental conditions of its home range, just cannot be fully recreated because of where zoos are located and the climate of their location.^6,7

“These limitations,” the authors speculate in their paper,¹ “may impact the welfare and health of zoo-managed species, including black and white rhinoceroses.”

One factor especially difficult to recreate in a zoo setting is proper vitamin D exposure, which comes in two main forms: ergocalciferol and cholecalciferol. Ergocalciferol mostly comes from plants after microorganisms like fungi on the plant surface get exposed to UVB rays from the sun. Cholecalciferol, on the other hand, is mainly produced when an animal's skin is directly exposed to UVB light, though a small amount can also come from food sources like fish and a few plant species.^8,9

What Factors Influence Vitamin D Levels in Zoo-Managed Rhinos, and Does That Vary by Species, Sex, Age, Season, Location, or Reproductive Status?

The Cincinnati Zoo researchers looked at whether vitamin D levels in the rhinos varied based on things like species, sex, age, the season, where the animal was located, or, for females, their reproductive status. One form of vitamin D, 25OHD2, was not even detectable in over half of the white rhino samples and in 80% of the black rhino samples. The other form, 25OHD3, told a different story; its levels changed noticeably depending on the season and location, tending to be higher in summer and in places that get more sunlight. However, this form of vitamin D did not seem to be linked to the rhino's species, sex, age, or reproductive status.¹

“These findings,” write the authors of this paper,¹ “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.”

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References

1. Windle, S.; Roth, T. L. Vitamin D Status in North American Managed Black Rhinoceros (Diceros bicornis) and White Rhinoceros (Ceratotherium simum). Conserv Physiol. 2026, 14 (1), coag062. DOI: 10.1093/conphys/coag062
2. Ricketts, V.; Dierenfeld, E. S.; Sauer, C. et al. Feed Intake and Dietary Composition of Iron (Fe), Copper (Cu), Vitamin E, and Tannic Acid of Five Captive Black Rhinoceros (Diceros bicornis) in a UK Collection. Zoo Biol. 2021, 40 (1), 52-58. DOI: 10.1002/zoo.21580
3. de Azevedo, C. S.; Cipreste, C. F.; Pizzutto, C. S. et al. Review of the Effects of Enclosure Complexity and Design on the Behaviour and Physiology of Zoo Animals. Animals (Basel) 2023, 13 (8), 1277. DOI: 10.3390/ani13081277
4. Martelli, P.; Krishnasamy, K. The Role of Preventative Medicine Programs in Animal Welfare and Wellbeing in Zoological Institutions. Animals (Basel) 2023,13 (14), 2299. DOI: 10.3390/ani13142299
5. Fens, A.; Clauss, M. Nutrition as an Integral Part of Behavioural Management of Zoo Animals. J. Zoo Aquar. Res. 2024, 12 (4), 196-204. DOI: 10.19227/jzar.v12i4.786
6. Liu, H.; Duan, H.; Wang, C. Effects of Ambient Environmental Factors on the Stereotypic Behaviors of Giant Pandas (Ailuropoda melanoleuca). PLoS One 2017, 12 (1), e0170167. DOI: 10.1371/journal.pone.0170167
7. Doyle, C.; Rally, H.; O’Brien, L. et al. Continuing Challenges of Elephant Captivity: The Captive Environment, Health Issues, and Welfare Implications. PeerJ2024,12,e18161. DOI: 10.7717/peerj.18161
8. Boland, R.; Skliar, M.; Curino, A. et al.Vitamin D Compounds in Plants. Plant Sci. 2003, (164) 3, 357-369. DOI: 10.1016/S0168-9452(02)00420-X
9. Jäpelt, R. B.; Didion, T.; Smedsgaard, J. et al. Seasonal Variation of Provitamin D2 and Vitamin D2 in Perennial Ryegrass (Lolium perenne L.). J Agric Food Chem.2011, 59 (20), 10907-12. DOI: 10.1021/jf202503c