Paws For Thought

EDITOR’S NOTE: Paws for Thought is penned by Dr. Janice Mitchell, a veterinarian with Island Animal Hospital and Little Current Veterinary Service offering advice and best practices for Manitoulin pet parents.

The Mousetrap

by Dr. Janice Mitchell

The May long weekend is coming up and this often means the official opening of the camp/cottage/cabin. This brings with it the excitement and anticipation of sunny days ahead and yet there is a danger that may sometimes lurk within these summer abodes. In the previous fall, bait traps may have been laid out for marauding and invading mice and these may pose a great danger for your pets. This month’s topic: mouse poisons, otherwise known as rodenticides.

Rodenticides are not all the same. When I first learned about them in vet school, the list was simple as it boiled down to one kind, with a couple of variations. These were the warfarin kind of poisons, the ones that when ingested, would cause little Mickey or Minnie Mouse to bleed out. These are called the ‘anticoagulants’ and most of us are familiar with these as warfarin is used as a preventive in human medicine for people who may have been diagnosed previously with threatening blood clots. When a dog or cat eats an anticoagulant mouse poison, it does the same thing it does to a mouse: it knocks out the body’s ability to clot blood. It may take a day or it may take a few days, but eventually they start bleeding. It could be anywhere: lungs, joints, eyes, brain. This does sound nasty, and can be, however the good news is that it’s very treatable if it’s caught early on before the bleeding begins in one of those bad places. The antidote is vitamin K, and it works quite well. For patients that are bleeding, they may need some extra treatment as well, like a blood transfusion, but the vast majority of dogs (and rarely cats—they’re pretty smart) that ingest anticoagulant mouse poison do pretty well with appropriate treatment.  

So, what are the variations? These anticoagulants can be either first or second generation rodenticides. First-generation anticoagulants, such as chlorophacinone, diphacinone and warfarin, include the anticoagulants that were developed as rodenticides before 1970. These compounds are much more toxic when feeding occurs on several successive days rather than on one day only. 


generation anticoagulants, such as brodifacoum and bromadiolone, were developed beginning in the 1970s to control rodents that are resistant to first-generation anticoagulants. Second-generation anticoagulants also are more likely than first-generation anticoagulants to be able to kill after a single night’s feeding. These compounds kill over a similar course of time but tend to remain in animal tissues longer than do first-generation ones. These properties mean that second-generation products pose greater risks to non-target species that might feed on bait only once or that might feed upon animals that have eaten the bait.  

This sounds downright scary however there is a subtle silver lining. Under new federal rules, sales of highly toxic second-generation anticoagulant rodenticides are restricted to professionals. Public retail sales of less-potent, first-generation poisons must include bait stations to further reduce unintended poisonings.  As Martha Stewart would say, “it’s a good thing.”

However, anticoagulants aside, there is a new bad kid on the block that is registered for use for rodent control in Canada. Enter bromethalin. Bromethalin is downright terrifying. It is a potent neurotoxin that causes irreversible brain swelling, seizures and paralysis. There is no antidote. It is usually fatal if accidentally ingested. This is one nasty poison.

This is where I would like to gently suggest that if you are needing some rodent control, resort to either adopting a good ol’ mouser cat (there are many that need homes) or use the tried and true Victor mouse traps. None of these options are poisonous. I would also like to suggest that should you use any poison, know what it is and make 110 percent certain that your pet or kids cannot get into it. 

If your dog does get into it, get to the vet ASAP. Getting your dog to vomit up any rodent poison is of upmost importance, and to begin the rest of the decontamination process. If you are headed to the ER or your regular veterinarian for decontamination, make sure you bring the box the poison originally came in with you. This will help them know what they are treating. I can’t overstress how important this step is. Knowing what the poison is half the battle, and if your dog got into an anticoagulant, you’ll be able to rest that much easier.

On this positive note, I hope the holiday weekend is enjoyable and relaxing. Oh, did I mention that the porcupines are out tantalizing the dogs? Stay safe everyone!