Copper Metabolism in the Koala (Phascolarctos cinereus) as Indicated by a Ceruloplasmin Stimulation Test1
KEITH W. THOMAS, STEVEN McORIST, ROGER E. HUDSON, AND CHRIS J. McCAUGHAN2
Regional Veterinary Laboratory, Department of Agriculture, Bairnsdale, 3875, Australia
2Department of Agriculture, McCartin St., Leongatha 3953, Australia.
Tests to examine the copper status of herbivores were evaluated in lactating cattle (Bos taurus). Serum copper, erythrocyte-copper superoxide dismutase, and serum ceruloplasmin were measured prior to and following an injection of a physiological dose of copper. The change in ceruloplasmin activity 24 h posttreatment was found to be the preferred test and response time. This ceruloplasmin stimulation test was then used to examine the physiological copper status of seven free-living koalas. One koala had a ceruloplasmin stimulation of 125%, while three further koalas had ceruloplasmin stimulations of 18%, 56%, and 63%. In the remaining koalas the ceruloplasmin stimulations at 24 h were all <10%. From these stimulation effects, a reference range for koala serum copper levels was established. Serum copper levels less than 1.5 μmol liter-1 are considered deficient, 1.5-4.5 μmol liter-1 marginal, and greater than 4.5 μmol liter-1 adequate. Twenty-three healthy koalas from other sites had serum copper levels of 6.1 ± 0.5 (range 2.7-12.3) μmol liter-1 and ceruloplasmin activity of 8.5 ± 1.4 (range 1.9-24.7) mUml-1. Five healthy koalas were found to have fecal copper concentrations of 0.17 ± 0.07 mmolkg-1 dry matter (DM). It is possible that the finding of one koala with deficient and two with marginally deficient copper status was due to the overbrowsed state of their dietary Eucalyptus spp. It is concluded that some koalas may experience marginal nutritional status in certain conditions.