Most people know about the dangers of chocolate to dogs but many people have never heard of onion toxicity in pets. They’ve perhaps fed their dog foods containing onion such as leftover pizza, hamburger, or gravy and nothing happened. A small amount may not cause a problem since onion toxicity is dose dependent. However, onions in any form (raw, cooked, dehydrated or powdered in a seasoning) can create a life-threatening form of hemolytic anemia in dogs.


What Happens in Onion Toxicity?

Red blood cells carry a protein, hemoglobin, which delivers oxygen to the tissues and organs. Onions contain a substance called thiosulphate which dogs (and cats) lack the enzyme to properly digest. Thiosulphate causes oxidation of hemoglobin in canine red blood cells, which then forms clumps, weakening the cell membranes.

These clumps, called Heinz bodies, protrude from the cell and eventually cause rupture, shortening the life span of the cell. When enough red cells are destroyed, anemia occurs and the body is starved for oxygen. Garlic also contains thiosulphate but in smaller amounts.

A significant decrease in red blood cells can cause many problems including heart failure. The number of cells destroyed usually depends on the amount of onion eaten. However, some dogs can develop severe reactions even after eating very little onion.

Small amounts of onion fed over a period of time can create illness just as a one-time dose can, due to the gradual build-up of Heinz bodies. On the other hand, some minor cases of onion toxicity may go undetected due to damage of fewer red blood cells. Symptoms sometimes take several days to manifest.


Symptoms of Onion Toxicity

  • Weakness and lethargy
  • Vomiting
  • Diarrhea
  • Difficulty breathing
  • Pale or bluish gums
  • Bloody urine
  • Jaundice
  • Decreased appetite
  • Increased heart rate
  • Severe toxicity can be fatal
  • Treatment of Onion Toxicity

If ingestion was recent, decontamination and intravenous fluids are traditional treatment. If anemia is severe, a lengthy hospital stay and a blood transfusion may be necessary.

Preventing Onion Toxicity

Onions are common in many human foods, including some baby foods, hush puppies, sandwich meats, canned spaghetti, gravies, fast foods, and many prepared meals. Check ingredients carefully in any table food before treating your dog to a snack. Avoid adding onions in any form to homemade dog food recipes. Make sure garbage is kept covered and away from dogs.