CHOLECALCIFEROL TOXICITY AND ITS ENHANCEMENT BY CALCIUM-CARBONATE IN THE COMMON BRUSHTAIL POSSUM

The common brushtail possum (Trichosurus vulpecula), an introduced pes t in New Zealand, is susceptible to cholecalciferol (vitamin D-3), whi ch is marketed as a rodenticide in many countries. To evaluate choleca lciferol for possum control we offered 242 caged adult possums cereal pellets containing cholecalciferol on its own or with calcium carbonat e. Mortality was recorded for two weeks after presentation. For cholec alciferol on its own the LD(50) was 16.8 mg kg(-1) (95% confidence int erval 11.6-21.9 mg kg(-1)), but the addition of calcium carbonate redu ced this to 9.8 mg kg(-1) (95% confidence interval 7.0-12.7 mg kg(-1)) . When the sexes were analysed separately, the reduction of the LD(50) by the addition of calcium carbonate was significant only in females. The addition of calcium carbonate appeared to result in a more predic table outcome as shown by the reduced confidence intervals. For possum control, adding calcium carbonate to cholecalciferol bait would impro ve the bait's efficacy, decrease the amount of toxic material needed, and reduce the cost of bait production.