Pets and Onions

Each Layer Can Poison Your Pets

Onions

Many people love onions, and there are plenty of foods that we enjoy that contain them. As always, we must remember that what is great and tasty for us can be extremely harmful for our pets.

Onions contain an ingredient called thiosulphate which is toxic to cats and dogs. The ingestion of onions causes a condition called hemolytic anemia, which is characterized by damage to the red blood cells. Onion toxicity can cause the red blood cells circulating through your pet’s body to burst.

Symptoms of this condition include breathlessness, lethargy, diarrhea and vomiting. Your pet also could lose interest in food as a result of this type of poisoning. It may take up to two to four days after your pet eats the onion for symptoms to appear.

Are All Onions Dangerous To Pets?

All onions — whether cooked or raw — are a danger to your pet. It takes a very small amount of onions to poison your cat or dog.

Consumption of as little as 5 g/kg of onions in cats or 15 to 30 g/kg in dogs has resulted in clinically important hematologic changes. Onion toxicosis is consistently noted in animals that ingest more than 0.5% of their body weight in onions at one time.*

About 600 to 800 grams of onions can cause acute toxicity. Your pet can also become poisoned by eating extremely small amounts of onions over a period of time.


If you suspect your pet has consumed some type of onion, call your veterinarian immediately.

Specific Foods to Think About

Green onions

Onions are a common ingredient found in many of the foods we eat — including foods you might not consider a danger to your pet. Make sure these foods do not contain any type of onion before you consider letting your pet indulge:

  • Pizza
  • Tomato sauce
  • Chinese food
  • Some baby foods

"Onion toxicity can be very serious and expensive to treat,” says Dr. Tina Swan, a veterinarian on staff with VPI Pet Insurance.

Swan, who specializes in animal emergency care, recalls diagnosing a patient with food toxicity symptoms. “I had a young dog with signs of partial paralysis and weakness of his back legs,” she says. “The clue to the problem was that the owner had fed the dog some macadamia-crusted salmon with sauteed onions the night before. It can be difficult to determine what causes a toxic reaction in pets, especially if they've eaten table scraps.” 

The best way to avoid accidentally poisoning your pet? Swan always advises clients not to feed their pets table scraps. “Many sources of onion (cooked or raw) have the potential to cause toxicity in pets including onion powder which is in many foods in varying amounts. Although it does take a certain amount to cause a problem, this can be hard to gauge in table scraps.”

What to Do If Your Pet Is Poisoned

If you suspect your pet has consumed some type of onion, call your veterinarian immediately. The condition can be treated, but it’s important to seek medical attention at the first suspicion of poisoning. Always keep an emergency veterinary clinic phone number and address handy in case your veterinarian is not available.

The condition, if severe, can require significant hospital time and in extreme cases a blood transfusion might be necessary.


Want to learn more about toxic foods for pets? Read about chocolate toxicity and raisin and grape toxicity.


Return to the VPI Pet HealthZone


*"Allium Species Poisoning in Dogs and Cats," R.B. Cope, BSc. BVSc, PhD

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