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Secondary Poisoning

Secondary Poisoning refers to one animal being poisoned after consuming the flesh of another animal which has digested the poison. According to experts, residues of digested anticoagulants (bromadialone, brodifacoum, diphacinone) can be found in the livers of poisoned rodents. Thus animals can ingest the anticoagulants when they consume the livers. Secondary ingestion is when one animal consumes a rodent which has undigested bait in its gut or mouth. It's much more of a concern with rats because they can consume up to 30 grams of bait per day. Secondary ingestion is considered to be a component of seccondary poisoning.

Whether or not an animal can become ill or die from secondary poisoning depends on several factors: inherant toxicity of the rodenticide, the sensitivity of the animal ingesting the poisoned carcass, the amount of the toxicant, and the time sequence of the bait ingested. It typically involves repeated feedings on poisoned carcasses over several days or longer.

Secondary poisoning is theoretically possible, but realistically, highly unlikely. Most of the anticoagulant baits are formulated with low dosages of active ingredients ranging from 25 to 50 ppm. Even with primary poisoning, a 20-pound dog would need to consume a minimum of 1.6 to 96 ounces of two of the most popular bait actives (brodifacoum and bromadialone) to obtain the value needed for a single-dose poisoning.

Multiple feedings of these baits over a prolonged period would require significantly less dosages. The chances of an average dog, etc. consuming enough rats on a periodic basis to accumulate enough poison to cause secondary poisoning is slim.

The most likely scenario conductive to secondary poisoning would be in those cases of severe or chronic rodent (particularily rats) infestations where many rodents would be poisoned over the course of several days or weeks. It would need to be coupled with hungry dogs, cats or some other free ranging animal exhibiting a daily opportunistic foraging strategy.

Take special precautions in farm situations where "farm cats and dogs" are fed only intermittently or not at all. These dogs and cats might feed on any dead, accessible rodents. In zoos, exotic animal farms and some confined livestock operations special precautions must be considered. Envisions scenarios conductive to secondary poisoning situations. Also some captive mammals and carnivorous birds may have sensitivities to anticoagulant baits - even in small amounts. Work with the zoo vets to avoid secondary rodenticide hazards.

In conclusion prevent primary poisoning for occurring by not allowing the baits to be accessible to any companion or non-target animals. To prevent secondary poisonings, ensure that poisoned rodents are picked up dailyand either buried or incinerated. For sensitive environments, try to confine or move any free-roaming non-target animals during peak time when poisoned rodents might be available. In cases of accidental ingestion suggest a trip to the vet to be sure. So it pays to always play it safe.

Condensed from "Secondary Poisoning Concerns with Rodent Baits", Dr. Bobby Corrigan, c1998.

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