Vitamin K 3 in Feedstuffs: Antidotal Effects in Captive Anticoagulant-Resistant Rats and Mice

Vitamin K in animal feeds may serve as an antidote to anticoagulant rodenticides. Thus, we investigated the relationship between addition of vitamin K3 (menadione sodium bisulphite) to a laboratory diet at levels frequently added to animal feedstuffs, and the selection of anticoagulant resistance in Norway rats (Rattus norvegicus: called rats) and house mice (Mus domesticus; hereafter called mice). We observed increased survival in anticoagulant-resistant rats exposed to anticoagulant rodenticides; however, we did not observe increased survival in an anticoagulant-susceptible strain of rats or in anticoagulant-resistant resistant or susceptible mice. We observed increased survival in 3 different strains of anticoagulant-resistant rats, that were fed the anticoagulant rodenticide difenacoum. Vitamin K3 at 5 mg/kg of diet acted as an antidote to the toxic effects of bromadiolone (P = 0.0001), brodifacoum (P = .0138), and flocoumafen (P = 0.2351), as well as difenacoum (P = .0003) in a Homozygous Hampshire (HH) strain of anticoagulant-resistant laboratory rats derived from wild rats trapped in the county of Hampshire, United Kingdom. Reduction of the concentration of vitamin K3 to 1 or 2 mg/kg of diet lowered the proportion of HH strain rats surviving difenacoum poisoning to the level that survived in the absence of additional vitamin K3. We conclude that vitamin K, in animal feedstuffs will enhance the survival and selection of anticoagulant-resistant rats. Management of anticoagulant-resistant rat populations could be achieved by reduction in the levels of vitamin K, supplement in animal feeds, and ending the practice of mixing rodenticide concentrates with animal feeds.