Summer and Winter Seasonal Changes in Vitamin D Status of Captive Rhinoceros Iguanas (Cyclura cornuta)

Abstract Four long-term captive adult rhinoceros iguanas (Cyclura cornuta) on display at the Dallas Zoo (Dallas, TX) were maintained for several years in an outdoor enclosure in the summer and in a smaller indoor enclosure in the winter. While fully exposed to sunlight and given the opportunity to supplement their diet with live vegetation each summer, they were deprived of the benefits of full sun exposure, including ultraviolet B (UVB) exposure, and they received no dietary vitamin D for several months each winter. Maintained with this protocol, the animals seemed healthy and they reproduced. However, increasing awareness of the important role of UVB in vitamin D–mediated calcium metabolism and the potential health risk of UVB and vitamin D deprivation stimulated us to focus more on seasonal changes in vitamin D status and possible subtle changes in health status throughout winter. From September 2008 to October 2010, an 85% decline in the serum 25-hydroxyvitamin D3 (calcidiol) concentrations was measur...