Warfarin-resistance genotype determination in the Norway rat,

The 2-stage determination is based on changes in blood coagulation activity brought about both by the administration of warfarin in conjunction with vitamin KJ epoxide and by feeding a vitamin K-free diet for 4 days. When it was applied to laboratory-bred rats of known warfarin-resistance genotype, 35/35 homozygous susceptible, 44/44 homozygous resistant and 131/133 heterozygous rats were correctly classified. This method was equally effective in identifying the genotype of wild rats carrying the warfarin-resistance gene, Rw2 • The procedure is rapid and accurate. Ever since resistance to the anticoagulant rodenticide warfarin was first reported (Boyle, 1960) there has been a need for a rapid and accurate method for determining the susceptibility or resistance of rats to anticoagulants. Although a number of such methods have been described (Greaves & Ayres, 1967