What kills mice and rats but not dogs?

There are a few key differences between mice, rats, and dogs that determine what can kill the former two species but not dogs. In this article, we’ll explore those differences and look at the most common rodenticides and their mechanisms of action to understand why they are toxic to mice and rats but not dogs.

Size and metabolism

The most fundamental difference is size – mice and rats are much smaller than dogs. An adult mouse may only weigh 30 grams while a large dog can weigh 50 kilograms or more. This size difference means mice and rats have a much faster basal metabolism compared to dogs.

A mouse’s heart beats around 500 times per minute while a dog’s heartbeat is typically 60-120 beats per minute at rest. The faster heartbeat and metabolic rate of rodents means they process toxins much more rapidly than larger animals like dogs.

Size also affects the dosage of toxins needed to be lethal. A dose of poison that kills a 30 gram mouse may have little or no effect on a 5,000 gram dog. The small body size and rapid metabolism make mice and rats much more vulnerable to metabolic poisons and rodenticides.

Differing biology and physiology

Beyond size and metabolic rate, there are a few key physiological and biological differences between mice/rats and dogs that alter toxicity:

  • Liver function – Mice and rats have livers that are less efficient at detoxification than a dog’s liver.
  • Kidney function – A dog’s kidneys are more efficient at filtration and excretion of toxins compared to rodents.
  • Blood-brain barrier – Dogs have a more robust blood-brain barrier that keeps poisons from reaching the brain.
  • Emesis – Dogs have an emetic reflex that allows them to vomit toxins back up. Mice and rats lack this vomiting ability.

These factors allow dogs to be relatively resistant to poisons that are lethal for smaller rodents. The differences in size, metabolism, and physiology make mice and rats vulnerable while protecting dogs.

Common Rodenticides

There are several classes of chemical poisons that are commonly used as rodenticides. The main ones include:

Anticoagulant Rodenticides

These include chemicals like brodifacoum, bromadiolone, and difethialone. They work by preventing blood clotting through blocking vitamin K metabolism. Rodents eat the bait and will die from internal bleeding within days.

Anticoagulants are highly toxic to mice, rats, and other small mammals due to their rapid metabolisms. Dogs are relatively resistant thanks to a slower metabolic rate and higher body mass. A dog would need to ingest a large quantity of anticoagulant bait to receive a lethal dose.

Cholecalciferol (Vitamin D3)

Cholecalciferol poisons rodents by causing a buildup of calcium in the blood, leading to kidney failure. Dogs are largely unaffected by cholecalciferol because their kidneys are much more efficient at excreting excess calcium.


Bromethalin is a neurotoxin that causes swelling in the brains of rodents, leading to paralysis and death. Dogs have a more robust blood-brain barrier that prevents bromethalin from reaching toxic levels in the brain.


Strychnine works by blocking inhibitory neurotransmitters in the brain and spinal cord. This leads to overstimulation of muscles and painful convulsions. Mice and rats are killed by strychnine at doses that wouldn’t affect a larger dog.

Zinc Phosphide

Zinc phosphide reacts with stomach acid to release phosphine gas. This disrupts mitochondria and causes organ damage. The smaller stomach size of rodents allows a lethal dose of phosphine to be released.

In general, the fast metabolism, small size, and inefficient detoxification abilities of mice and rats make them vulnerable to metabolic rodenticides. Dogs have biological protections that render them resistant to the same poisons.

Safe Rodent Control Around Dogs

When dealing with a rodent problem in a home with dogs, it’s crucial to use a product that is safe for pets. Here are some options:

Physical Traps

Snap traps, electric traps, and other physical kill traps can be very effective against mice and rats but pose no risk to dogs. Traps allow you to eliminate rodents without chemicals around pets.

Natural Rodenticides

Some EPA approved rodenticides derived from nature have low toxicity for dogs. These include citric acid, clove oil, and eugenol derived from various plants. Always check labeling for pet safety.

Limit Access

Keep dogs away from areas where you place baits and make rodenticides inaccessible to minimize the risk of accidental ingestion. This can prevent exposure even from lower toxicity products.

Careful Handling

Follow all label safety precautions when using any rodenticides, including wearing gloves and avoiding contact with bare skin. Clean up uneaten bait to prevent exposure.

With careful product selection and proper usage, rodents can be safely controlled even in homes with pet dogs. But extra precautions are needed compared to pest control in a home without animals.


Mice and rats have a biology and metabolism that leaves them highly vulnerable to many types of rodenticides. Dogs are resistant to the same poisonous chemicals thanks to larger body size, more efficient filtration organs, and other protective mechanisms.

However, dogs can still be unintentionally poisoned through improper rodenticide usage. When controlling rodents in a home with dogs, physical traps or natural low-toxicity poisons are the safest options. With careful baiting procedures, even more toxic rodenticides can also be used safely around pets.

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