Comparative toxicity of the two anti‐coagulants, coumatetralyl and warfarin, to wild house‐mice (Mus musculus L.)

SUMMARY In comparative tests using individually caged wild house‐mice ( Mus musculus L.) coumatetralyl at 0·05 % in an oatmeal bait‐base was found to be as acceptable as plain bait and as acceptable and as toxic as warfarin at 0·025% (the standard dosage). It was less readily accepted at 0·1 or 0·2% in the same bait‐base or at 0·05% in a proprietary bait formulation. In further tests with suspected warfarin‐resistant mice, coumatetralyl at either 0·05, 0·1 or 0·2% proved more toxic than warfarin at either 0·025, 0·1 or 0·2% respectively. However, some individuals survived 21 days feeding on each of these concentrations of coumatetralyl and, in field and laboratory trials, 0·05 and 0·1% coumatetralyl baits failed to control warfarin‐resistant mouse populations after 3–5 weeks. It is concluded that coumatetralyl is a suitable alternative poison to warfarin for use against mice that are susceptible to anti‐coagulants but that it is unlikely to control warfarin‐resistant populations effectively.