Impacts of UVB provision and dietary calcium content on serum vitamin D3, growth rates, skeletal structure and coloration in captive oriental fire‐bellied toads (Bombina orientalis)

• Published in: Journal of animal physiology and animal nutrition 2015-04, Vol.99 (2), p.391-403
• Main Authors: Michaels, C. J, Antwis, R. E, Preziosi, R. F
• Format: Article
• Language: English
• Subjects: amphibians; Animal Feed; Animal Husbandry; Animals; Anura - physiology; blood serum; Bone Development - drug effects; Bone Development - radiation effects; Calcium; calcium metabolism; Calcium, Dietary - pharmacology; cholecalciferol; Cholecalciferol - biosynthesis; Cholecalciferol - blood; color; developmental orthopedic disease; diet; ex situ; ex situ conservation; Gryllidae; gut-loading; insects; Metabolism; Pigments, Biological - metabolism; Reptiles & amphibians; Sunscreen; Toads; Ultraviolet radiation; Ultraviolet Rays; UVB radiation; vitamin D3
• ISSN: 0931-2439; 1439-0396
• DOI: 10.1111/jpn.12203

Many amphibian species are dependent on ex situ conservation interventions for their long‐term persistence. However, projects have been jeopardised by husbandry issues involving poor calcium metabolism and nutritional metabolic bone disease (NMBD). Healthy calcium metabolism requires appropriate dietary calcium content and access to vitamin D₃. In many animals, vitamin D₃can be photobiosynthesised in skin exposed to UVB radiation, as well as extracted from the diet, but the extent of vitamin D₃photobiosynthesis in amphibians is poorly known. Additionally, prey insects for captive amphibians are deficient in calcium and calcium content must be artificially increased, but the effects of different levels of augmentation and their interaction with UVB exposure are also little understood. We fed captive fire‐bellied toads (Bombina orientalis) with crickets augmented to contain 5% and 10% calcium and housed them with and without UVB exposure. Despite additional dietary vitamin D₃supplementation, we found that toads exposed to UVB radiation exhibited significantly higher serum vitamin D₃levels, indicating that this species may partly rely on photobiosynthesis sources of vitamin D₃. These data are the first to show a direct link between UVB exposure and serum vitamin D₃in an amphibian. We found significant positive effects of UVB exposure and 10% dietary calcium content on skeletal structure, as well as complex interactions between treatments. We also found UVB radiation exposure resulted in more rapid natural coloration acquisition. Together, this indicates that standard calcium plus vitamin D₃supplementation methods may not fully substitute for UVB exposure and for increased feeder insect calcium content. This may have implications for the success of ex situ amphibian conservation, as well as for the welfare of captive amphibians in general. Our data lend support for the provision of UVB radiation for captive, basking amphibians.