What If My Cat or Dog Eats a Poisoned Mouse?

Simply stated, if your pet eats a poisoned mouse, rat, or other small mammal, it too will be poisoned! The pesticide labels clearly state that if your pet consumes a poison designed for a small mammal there are likely to be serious or fatal consequences. But it is less clearly stated what might happen if your pet eats a mouse or mole, etc. that is already dead after being poisoned. This effect is called secondary toxicity, and although poison labels don't say much about it, you should be aware that it can be a problem.

Most rodent poisons that are available for household use are some variety of blood thinner. They block the working of vitamin K which is required to produce clotting factors in the blood. They are slow-acting, and long lasting. Once an animal eats the poison and uses up the clotting factors in its blood it will be unable to make more. Then any small bruise or wound will continue to bleed until the animal is weakened by the blood loss, and dies.

Birds of prey are the most common victims of secondary toxicity because they can easily capture small animals that are weakened from the blood loss due to poisoning. Therapy requires treatment with doses of Vitamin K over a period of several weeks until the birds are once again able to produce it on their own. During the treatment time they will exhibit the same symptoms as the primary target of the poison: loss of appetite, extensive bruising, continual bleeding of any open wounds, and lethargy.¹ This is what your pet can look forward to if it ingests a poisoned animal.

Common over the counter poisons which are blood thinners include D-Con, One-Bite, Mole Patrol, Victor, and Ramik. This list is NOT complete. Active ingredient names to watch for are Warfarin, Brodifacoum, Coumadin, Difethialone, Diphacinone, and Chlorophacinone. There may be other names. These chemical names appear in the list of active ingredients which, in the United States, must be printed on the product.

Material Safety Data Sheets (MSDS) for some household pesticides are available at Aubuchon Hardware. These are standardized forms listing all the hazards of nearly every chemical from common table salt to complex hazardous materials. If you scroll down to Section 12 of the sheet the Ecotoxicity is listed. Most of these poisons say "This product is toxic to birds, fish, and wildlife. The product can pose a secondary hazard to birds of prey and mammals." This is the phrase that means DON'T LET YOUR PET EAT A POISONED ANIMAL.

You might not even know what is making your pet weak or ill unless you realize what has happened. Therefore, if you or your neighbors use rodenticides and you have pets you need to be vigilant. Not only should you make sure that the poison itself is not accessible to your cat or dog, but watch for dead animals and remove them before your pet gets to them. Usually rodents will go underground or deep in the walls to die, but occasionally you will find one out in the open.

The good news? "The rule of thumb for dogs is that a lethal dose consists of between 0.2 and 4 milligrams of brodifacoum for every kilogram of body weight. So, a 75-pound dog would need to eat more than 4 ounces of d-Con mouse poison." ² But Vitamin K therapy would be required.

Plain old mouse traps sound better and better to me every year!

1. Tufts Cummings School of Veterinary Medicine

2. Can Mouse Poison Kill You? by Brendan I. Koerner