Field trials of calciferol combined with warfarin against wild house-mice (Mus musclus L.).

A combination of calciferol (vitamin D(2)) and warfarin, each at 0.025% in medium oatmeal bait, failed to control six of seven house-mouse (Mus musculus L.) populations infesting urban and farm buildings. In three further treatments with both calciferol and warfarin at 0.05% in dehusked canary seed bait plus 5% corn oil, mortality, estimated from the consumption of pre- and post-treatment census bait, ranged between 94.2 and 97.4%. Finally, among sixteen treatments done with calciferol at 0.1% and warfarin at 0.025% in various cereal baits, the best results (97.0-100%) were obtained in six treatments where the bait-base was whole canary seed; this was so whether the poison bait was applied directly or after a 3-day pre-baiting period. It is concluded that calciferol at 0.1% plus warfarin at 0.025% is an effective combination against house-mice, especially when used with whole canary seed. The role played by warfarin in the poison mixture needs to be investigated further.