Vitamin K deficiency syndromes in warfarin-resistant brown rats (Rattus norvegicus)

Resistance to the anticoagulant rodenticide warfarin and an increased vitamin K requirement appear to be pleiotropic effects of the gene Rw2. A comparison of pup mortality in F2 (Rw1Rw2 x Rw1Rw2) and backcross (Rw1Rw2 x Rw1Rw1 or reciprocal) matings of wild brown rats in the laboratory revealed significantly greater losses in the F2 litters at 4-8 weeks of age. Some deaths could be attributed directly to haemorrhage resulting from vitamin K deficiency. A newborn warfarin-resistant rat from an F2 litter showed bleeding from the umbilicus and the anus, and died from internal haemorrhage at 18 weeks of age. Another warfarin-resistant male rat dying at the same age had a grossly enlarged skull.