Abstract

Hip and shoulder dysplasia are prevalent problems in the San Diego Zoo koala colony. While the cause of the dysplasia appears genetic, abnormal bone development due to nutritional insufficiencies needed investigation. It is unknown if vitamin D deficiency occurs in koalas managed indoors without access to direct, unfiltered sunlight. Few plants have significant concentrations of vitamin D₂ and D₃ and therefore koalas may be reliant on exposure to UVB light. Serum samples from 22 zoo-based and 19 free-ranging koalas were analyzed for calcium, phosphorus, and vitamin D. Calcium values differed between zoo-based and free-ranging koalas [means of 10.6 and 10.3 mg/dl, respectively (p=0.047)]. Phosphorus values differed between zoo-based and free-ranging koalas [means of 3.48 and 5.25 mg/ml, respectively (p<0.0001)]. Initial testing for 25-dihydroxyvitamin D₃ questioned the validity of the testing method (RIA kit for humans) when 17 of the 19 free-ranging koalas failed to register a value, while the mean of the zoo-based koalas was 8.9 nmol/l. A second laboratory was consulted and preliminary testing, using liquid chromatography mass spectroscopy, is suggestive that zoo-based and free-ranging koalas have similar 25-dihydroxyvitamin D₂ values, but zoo-based koalas have non-detectable 25-dihydroxyvitamin D₃ values, while free-ranging koalas have values approximately half that of their 25-dihydroxyvitamin D₂ values. Further sampling and testing are required before conclusions can be made.