What owners can watch for, why the timing is so cruel, and why not all rat poison is the same
The dog seems fine on Monday, but by Thursday he is quiet, a little wobbly, perhaps breathing faster than usual, and there may be a smear of blood somewhere it should not be. Typically, nobody saw him eat anything unusual, but he definitely isn’t ‘right’. The vet asks about rat poison and the owner says there might be some in the garage, but that it was put out days ago, and the dog was never seen to go anywhere near it.
This is the typical presentation of anticoagulant rodenticide poisoning, and the reason it kills dogs who could have been saved. The gap between eating the bait and looking ill is days, so by the time anything is visibly wrong, the poison has had a long head start. It is worth all of us understanding how rodenticide poisoning works, because the knowing does most of the saving in these cases.
Winter peak
As the weather cools, rodents move indoors looking for warmth and food, and households respond by putting bait down. More bait in more homes means more chances for a dog to find it, and dogs are far more inclined than cats to eat the stuff, because many baits are cereal-based and formulated to be palatable to rodents, which makes them palatable to a dog too.
The bait does not have to be reached directly off the floor, either. A dog may dig out a block that was pushed into a wall cavity, find one a rat has carried and dropped in the garden, or, less commonly, eat a poisoned rodent. That last route, secondary poisoning, is real but requires a dog to eat a fair number of poisoned rodents, so it is a much bigger risk for wildlife than for the average pet.
How the poison acts
Blood clotting depends on a set of clotting factors that the body can only manufacture with the help of vitamin K. Anticoagulant rodenticides block the enzyme that recycles vitamin K, so over a day or two the existing clotting factors get used up and are not replaced. The blood gradually loses its ability to clot, and the animal begins to bleed.
The cruelty of the poisoning is in the delay. The clotting factors already circulating keep working until they run down, which is why a dog can eat bait on Monday and look completely well until Wednesday or Thursday. In fact, clinical signs are said to typically begin around three to five days after ingestion. By then the poison is long absorbed, and the window in which simply emptying the stomach would have helped has closed.
When the bleeding starts, it is often hidden, which is the second trap. We expect blood we can see, but much of the bleeding happens internally, into the chest, the abdomen, the lungs, the gut or the joints. A dog bleeding to death internally may show nothing more specific than lethargy, weakness, pale gums, a swollen or painful belly, or laboured breathing. Visible bleeding from the nose, mouth, in the urine or as bruising under the skin does happen, but its absence is not reassuring in itself.
The signs to act on
Because the bleeding is usually internal, the signs are vague, and that is exactly why owners should treat known or suspected access to bait as the emergency, rather than waiting for something dramatic to appear. The things that should prompt a call to a vet include:
• Unusual lethargy, weakness or collapse, especially if it comes on over a day or two.
• Pale gums, which can be a sign of blood loss.
• Faster or laboured breathing, or a cough, which can mean bleeding into the chest or lungs.
• A swollen, tender abdomen.
• Bleeding that does not stop, or bruising appearing under the skin.
• Blood in the urine or stool, from the nose or mouth, or prolonged bleeding from a small wound.
• Lameness or swollen joints, from bleeding into a joint.
The single most important point is this: if a dog is known or suspected to have eaten rat bait, the right time to see a vet is immediately, not once he looks sick. A dog seen within a few hours of eating bait can often be treated before any harm is done at all, by emptying the stomach and starting the antidote. A dog brought in already bleeding is a much harder and more dangerous case to treat.
The antidotes
For this specific poison, there is a genuine antidote, which is great news. Vitamin K1, given as a course of tablets, replaces what the poison is blocking and allows normal clotting to resume. A dog caught early and treated properly has an excellent chance of survival.
Two details matter when it comes to vitamin K1. The first is that vitamin K1 is a prescription medicine, and it is not the same as the vitamin K sold in health shops, so treatment is not something to attempt at home. The second is that the course is long, often several weeks, because the second-generation baits most commonly sold today persist in the body for a long time. The temptation to stop the tablets once the dog looks better is dangerous, because the poison can outlast a short course and the bleeding can return. The course is finished when confirmed by a clotting test, and not before.
A severely affected, actively bleeding dog may also need a plasma or blood transfusion to replace clotting ability immediately, because the antidote takes a day or so to work. This requires hospital admission.
Not all rat poison is the same
Everything above applies to anticoagulant rodenticides, which for many years were the standard type, but they are not the only rat poison on the shelf now, and the other poisons are not treated in the same way at all.
Two other types of rodenticide matter for our dogs. Bromethalin is a nerve poison that causes tremors, wobbliness, paralysis and seizures rather than bleeding. Cholecalciferol, a concentrated form of vitamin D, raises blood calcium to the point that it damages the kidneys and other organs. Crucially, vitamin K1 does nothing for either of these. There is no simple antidote for these poisons, and the treatment is completely different.
The reason this matters so much to an owner is a fact that surprises most people (including us when we were putting together the article!): the colour, shape and size of the bait tell you nothing about which poison it contains. A green/blue block may actually be any of the three poisons. The only reliable guide is the active ingredient printed on the packaging, or the registration number.
The wider harm
There is a reason to care about rodenticide beyond the risk to one’s own dog.
The baits are potent enough to kill a rat with a single feed, but they also linger in that rat’s body for weeks to months, meaning a poisoned rat will die but does not die quickly. It grows slow and clumsy, which makes it easy prey, and everything that then eats it takes in the poison. This is how rat bait travels up the food chain and kills the very animals that control rats: owls, other birds of prey, and small predators.
This is not a theoretical concern; a study of predators in Cape Town found anticoagulant rodenticide exposure to be widespread, including in the city’s caracals, and local bird rehabilitation centres have long reported rodenticide poisoning as a major killer of owls and other raptors.
None of this is written to shame anyone; rodents in the home are a genuine health problem, and people reach for what works, but it is worth owners knowing that the most convenient product is often the most persistent one, and that the same properties that make it dangerous to a dog make it dangerous to a barn owl. Where rodent control is unavoidable, there are gentler routes: snap traps, which act instantly and leave no residue to travel up the food chain; sealing the gaps that let rodents in; removing the food that draws them; and, for those with the space, encouraging the owls that do the job at no cost and no risk. For anyone set on bait, a first-generation product, used in a covered bait station out of a dog’s reach, carries less of this long-lived secondary risk than the second-generation blocks that now tend to dominate the shelf.
The bottom line
Anticoagulant rodenticide is dangerous because it gives no warning at the moment it matters, and the signs, when they come, are easy to mistake for something less serious. The owner who understands that access to bait is itself the emergency, who acts before the dog looks ill, and who takes the packaging to the vet, has already done the most important part of saving their dog.
As with any suspected poisoning, this article is a guide to recognition and prevention, not a substitute for veterinary care. Any dog that may have had access to rodenticide should be seen by a vet without delay.
If a dog eats rat bait
• Phone a vet immediately. Do not wait for signs. The best outcomes come from dogs treated before they are ill.
• Take the packaging with you, or photograph it, including the active ingredient and registration number.
• Do not try to make the dog vomit at home unless a vet tells you to. Some cases need it, some do not, and the wrong choice can cause harm.
• Do not treat at home with vitamin supplements. The antidote is a specific prescription medicine and only works against one type of poison.
• Finish the full course of treatment given by the vet, however well the dog looks. Second-generation baits outlast a short course.
References
• Merck Veterinary Manual. Anticoagulant rodenticide poisoning in animals; rodenticide poisoning. • Pet Poison Helpline. Rodenticide reminder; veterinary rodenticide guidance on bait identification and type. • VCA Animal Hospitals. Anticoagulant rodenticide poisoning in dogs. • Serieys LEK et al. Widespread anticoagulant poison exposure in predators in Cape Town, South Africa, 2019. • Study of the contested ethics of rodent control in Cape Town, Journal of Urban Ecology, 2019.
