Abstract

Vitamin D metabolism is a complex process involving a balance of nutritional, environmental and behavioral factors.^1,2,6 The roles of calcium, phosphorus, ultraviolet radiation, pre-formed vitamin D and vitamin D precursors in reptile health are the focus of study for many investigators. In reptiles, imbalances of the myriad of factors contributing to biologically correct vitamin D metabolism has been documented to result in clinical syndromes such as fibrous osteodystrophy, dystrophic mineralization, and hypocalcemic tetany.³

Uromastyx spp. are herbivorous agamid lizards that have evolved to live in arid, hot climates. In the Wildlife Conservation Society’s collections of U. ornatus (Uo) and U. aegyptius (Ua), a disease process, which consists of mineral deposits in skin and periarticular regions, has been observed. Affected animals may develop multiple mineralized nodules which surround joints, diffusely invade skin and ultimately impair mobility. Analysis of the mineralized material in one case revealed the presence of calcium hydroxyapatite and calcium pyrophosphate dihydrate. Uric acid deposits, seen in articular gout, are not a component of this syndrome.

The goal of this investigation was to determine plasma 25-hydroxyvitamin D (25-OH-D) concentrations in captive Uromastyx spp., and to correlate those levels with radiographs and clinical signs. The hypothesis was that animals with radiographic lesions would have discernible differences in measurable vitamin D concentrations from animals without lesions. It was hoped that the data would aid in formulation of treatment protocols for clinically affected animals.

Twenty-two Uromastyx spp. (Uo=8, Ua=14) were evaluated. Animals from four WCS departments (Bronx Zoo Department of Herpetology [n=2], Bronx Zoo Children’s Zoo [n=10], Prospect Park Wildlife Center [n=1], and Central Park Wildlife Center [n=3]) and one private individual (n=6) underwent physical examination, radiography and blood collection from the ventral tail vein. Of the 22, seven (Uo=3, Ua=4) were considered clinically affected with one or more of the following: dermatitis, dystrophic mineralization, loss of range of motion in joints, and hypocalcemia. The affected animals also had radiographic lesions consisting of mineralization of the skin and/or multifocal periarticular mineralization.

25-OH-D was determined in samples from all 22 animals (7 affected, 15 unaffected) at Boston University using previously described methods.⁴ The mean concentrations and standard deviations (SD) are reported in Table 1.

Table 1. 25-(OH)-D concentrations (x±SD) in Uromastyx aegyptius and Uromastyx ornatus with and without dystrophic mineralization (x±SD)

For all Uromastyx examined, vitamin D₃ concentrations were lower (5–43 ng/ml) than those reported for clinically normal herbivorous lizards housed outdoors (>400 ng/ml).¹ However, none of the animals had evidence of metabolic bone disease or fibrous osteodystrophy. Dystrophic mineralization was seen in Uromastyx ornatus having lower vitamin D levels than unaffected animals. The finding of dystrophic mineralization associated with hypovitaminosis D is consistent with previously reported observations in green iguanas.⁵ In Uromastyx aegyptius, however, no difference in vitamin D concentrations were seen between affected and unaffected animals.

This study suffers from inconsistencies in blood sampling times vs. appearance of clinical lesions. In some cases, animals had advanced lesions at the time blood was collected for the vitamin D levels. It was beyond the scope of this study to collect dietary or husbandry data, so it is not possible to determine whether the low vitamin D levels reflect insufficiencies in ultraviolet radiation, over supplementation with other fat-soluble vitamins, and/or low environmental temperature.

The impetus to perform this study was to help clinicians develop treatment protocols for Uromastyx sp. that are affected with varying degrees of dystrophic mineralization. When presented with an animal that has mineral deposits in aberrant sites the quandary has been whether to treat the individual for hypo or hypervitaminosis D, hypo- or hypercalcemia and/or renal failure. Based on this investigation it appears that it is reasonable to treat clinically affected Uromastyx spp. with injectable vitamin D₃ as part of an initial therapeutic regimen. However, this treatment should be done in conjunction with husbandry measures to assure that the animal has access to appropriate ultraviolet radiation sources and adequate thermal conditions to allow for conversion of previtamin D₃ to vitamin D₃.

Acknowledgments

The authors gratefully acknowledge the cooperation and contributions of Bill Holmstrom, Bruce Foster, Tom Probst and Jim Breheny during the collection of samples for this study, and Michael Holick and Tai C. Chen of the Boston University Medical Center for analysis of the samples. This study was funded by a grant from the Species Survival Fund of the Wildlife Conservation Society.

Literature Cited

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