Trapping of rodents is a slow process and may take time to control the problem. Poisoning is an easier, quicker, and more economical way to control the problem, but it has its consequences. These consequences include the possibility of our pets (both dogs and cats) and wildlife (raptors, bobcats, coyotes, and mountain lions) ingesting the poison directly or indirectly through ingestion of a dead or dying rat. In studies in both California and New York, brodifacoum (D-con, Talon, Havoc) was found to account for 80% of the secondary poisonings by rodenticides. Brodifacoum and other commonly used rodenticides are currently under review by the Environmental Protection Agency (EPA) due to concerns about harmful effects on wildlife and the accidental poisonings of pets and children.
Rodenticide is the ingredient in mouse and rat poison. Typical active ingredients are: brodificoum, diphacinone, warfarin, bromadoline, and others. Most of these products include green dyes for a characteristic appearance; however, dogs and cats have poor color vision and to them these pellets may look like kibbled pet food. Anticoagulant rodenticides do not produce signs of poisoning for several days after the toxic dose has been consumed but eventually cause internal bleeding. The poisoned victim will show weakness and pallor (pale gums) but bleeding will likely not be obvious externally.
There are two basic types of rodenticide. The most common one works by causing a bleeding problem, the other by causing damage to the brain. Pets may be poisoned by eating rodenticide directly or secondarily by ingesting a rodent that has eaten the poison. Anticoagulant rodenticides exert their effect by inducing a secondary vitamin K-dependent coagulopathy leading to uncontrollable hemorrhage and death. They cause suppression of blood clotting by depleting vitamin K1 which is essential for clotting factor activation.
Warfarin, or broudifacoum-type rodenticides, cause bleeding problems three to five days after ingestion, although abnormal clotting of the blood can be detected earlier. If treatment is started before a bleeding problem develops, the risk of death and the cost of treatment are much lower. If rodenticide has been ingested, you may see bluish-green material in the vomit or stool. Clinical signs of toxicity may include (variations due to site of bleeding):
- Pale gums
- Black or bloody stool
- Bloody urine
- Difficulty breathing
- Coughing up blood
- Distended abdomen
Early treatment may include making the pet vomit, administering activated charcoal, cathartics, and vitamin K, which is the antidote for this type of rodenticide. Treatment at this stage should prevent bleeding. If bleeding has already started, treatment may also include plasma transfusion to provide clotting factors to stop the bleeding, blood transfusion if the animal is anemic, and other life saving procedures as indicated. As long as treatment is started before the animal bleeds to death, most pets survive, but earlier treatment is recommended. Animals that are elderly or juvenile and those with liver disease, hypothyroidism, or other underlying illnesses are more susceptible to anticoagulant rodenticides.
The second type of rodenticide, bromethalin, has no antidote. Signs may occur within 10 to 86 hours of ingestion, and may persist as long as 12 days. Even small amounts may be lethal. Signs include:
- Weakness of the back legs
- Poor appetite
If a pet is known to ingest this type of poison, the main focus is to try to prevent absorption by making the pet vomit, pumping the stomach, and administering charcoal and supportive treatment with IV fluids. If neurologic signs develop, treatment may decrease swelling in the brain and control seizures. However, the prognosis is very poor.
Should accidental exposure occur, immediately contact your local veterinarian or call the ASPCA Animal Poison Control Center for assistance (888) 426-4435, and be sure to have the container or package information readily available so that a proper identification of the rodenticide’s ingredients can be made for appropriate treatment.
If you have a large number of rodents in your area, try non-chemical methods first:
- Remove piles of yard debris, trash, construction waste, where rats or mice could make homes.
- Eliminate food sources. Don’t leave pet food outside. Keep wild birdseed and other materials rats or mice may eat (such as some organic fertilizers) in rodent-proof containers. Collect and remove fallen fruit from fruit trees in the yard.
- Exclude rodents from your home. Rodents can squeeze through amazingly small holes – 1/4 inch for mice and 1/2 inch for rats. Go around the outside of your house looking for openings and seal them with metal, hardware cloth, mortar, or concrete.