Secondary Poisoning Concerns With Dogs and Cats

What happens if my dog eats the mice that have died from poison rodent baits? Can they be poisoned as a second poison? How does primary poisoning differ from secondary ingestion?

These are very common questions by our residential customers. These questions are also of interest to rodent control practices around zoos, farms with livestock, and other facilities with animals.

Primary VS Secondary Poisoning

When an animal directly eats the rodent bait it is a primary poisoning. This would occur when an animal eats rodenticide that is not in a tamper-resistant bait station or in an accessible area. Primary poisoning is the most general way that pets and non-targeted animals get poisoned from rodent baits

Secondary poisoning occurs when an animal eats the flesh of a rat or mouse after they consumed the rodent bait. This occurs in anticoagulant rodent baits such as brodifacoum, bromadiolone, difethialone and diphacinone. Digested anticoagulants can reside in the livers of mice and rats after consuming the rodent bait. When an animal eats the entire carcass of poisoned rodents, they can ingest the anticoagulants. Another way the animal can consume the bait is to eat undigested bait that is in the mouth or gut of the rodent. This is not as much secondary as a primary way of ingesting the poison.

For secondary poisoning to occur, depends on a lot of factors. These factors include the amount of toxicant, the animal's general health and sensitivity and the timing of the bait ingested by the rodent. Some anticoagulants are single feeding baits, and some are multiple feeding bait. Multiple feeding baits require several feedings over a while for a lethal dose. Single feed baits are stronger. Since rats eat more bait than mice, secondary poisoning more frequently occurs with rat carcasses. Rats can eat up to 30 grams of rodent bait a day while mice only consumes up to 4 grams of bait.

Secondary Poisoning is Rare

Although secondary poisoning is possible, it is unlikely to occur. Anticoagulant baits are manufactured with low dosages of active ingredients that range from 25 parts to 50 parts per million. A 20 lb dog would need to consume a range from 1.6 to 96 ounces of baits such as Contrac (bromadiolone) or Final(brodifacoum) to get poisoned in both primary or secondary poisonings.

The chances of a pet to consume enough carcasses of a dead rat to accumulate sufficient poison for secondary poisoning would be low. It is more likely to occur with a high population of dead poisoned rats that are accessible, coupled with pets or non-targeted animals that are foraging for food due to hunger. Most pets are loved and fed well. They would need to be very hungry for them to eat many dead carcasses of rats.

More Typical Scenarios With Secondary Rodenticide Hazards

A more typical scenario would happen on a farm where farm cats or dogs are not fed well. These dogs and cats would forage for food where they have access, and eat enough dead rodents to curb their appetite. Exotic animal farms confined livestock and in zoos have animals where secondary poisoning would more readily occur. Some captive animals and carnivorous birds are very sensitive to anticoagulant baits in very small amounts. Always keep rodent bait in tamper-resistant bait stations to avoid direct poisoning. Try to keep the animals away from areas where the poisoned rodents might be available. Practice sanitation by cleaning up dead rodents and either incinerate or bury them.

It is necessary to inform the vet if your pet accidentally consumes the bait either directly or indirectly from secondary poisoning.