Control of Norway Rats with Residual Rodenticide Warfarin

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Abstract
Warfarin provides a completely new workable approach to rodent control. Because it does not cause acquired bait refusal (bait shyness), the compound is self-pre-baiting and may be used as a residual rodenticide. All rats tested withstood a single dose of warfarin at the rate of 50 mg./kg. 90% or more of rats given the compound by stomach tube for 5 consecutive days were killed by a total dosage of 5 mg./kg. or above. Warfarin was slightly less effective when given on alternate days. All of 10 rats offered poisoned bait at a concn. of 0.00625 mg./g., along with poison-free food,for 14 days, were killed; they took an average total of 2.87 mg./kg. Field trials against Norway rats, including some tests in an old focus of murine typhus and in places where 1080 and ANTU had previously been used without complete effectiveness,were successful even with concns. of 0.05 mg./g. of bait (0.005%). Yellow corn meal proved an effective bait. Secondary poisoning may occur if cats (and presumably dogs) eat several warfarin-poisoned rats over a period of days. Warfarin produces a typical pathology that can be recognized with almost complete certainity in something over 85% of rats killed by it. The cost and other limiting factors in the use of warfarin are discussed.
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