I am often asked about Best Practice for rodent control, and of course the best ways are natural and keeping places tidy to keep rat infestations away, but if one does have to use a rodenticide, then to use a multiple feed product reduces risk to owls …
Racumin is a Bayer product, distributed by Coopers in South Africa, which contains the active ingredient coumatetralyl. It ís a multiple feed rodenticide, meaning that a rodent needs to feed several times before becoming intoxicated, and that is over about 4 days. With most other rodenticides, rodents only need a single feed, although they may eat for a few days before they die.
So the rat needs multiple Racumin feedings to reach 16, 5 milligrams per kg body weight over 4 days. (Lethal dose oral for rats is 16, 5 mg/kg). Death is by inhibited blood coagulation (internal bleeding). (The antidote for accidental mammalian poisonings in Vitamin K, to be administered by a vet).
The link to owls:
For an owl to reach the lethal dose by multiple feeding is unlikely. Also the lethal dosage for birds is >2000 mg/kg (Japanese quail); = about 121 times less toxic to the quail than the rat, and then with an owl being heavier that the quail, again possibly a greater safety margin.
There are a few formulations of Racumin available, blocks, paste sachets and granules, and if placed in a way that pets and farm animals can’t get to it, in my opinion it’s the lowest risk rodenticide for farm use. Also then the most environmentally acceptable.
The liquid formulation is classed as Group 1, because of the possibility to ingest a lethal dose in a single event.
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