Onion Toxicity

Onions may make us humans cry but they do much, much worse in our canine and feline companions. Onions and dogs and cats are not a good match! Onions belong to a group of plants called the Allium species, which also includes leek, garlic, chives, shallots and scallions.  While they are tasty in human foods, these vegetables, whether raw or cooked, are extremely toxic to pets.

Onions and other Allium species contain organosulfides which are absorbed through the gut and converted into oxidants in the system.  These compounds are not removed by the cooking process, which makes onions toxic to our pets in any form.  The mechanism of toxicity is by oxidative hemolysis.  In simple terms, this means that the red blood cells (RBC) in the system become overloaded with oxidants to the point of bursting.  This destruction of red blood cells causes anemia (low RBC numbers).  As the main role of RBC’s in the system is to carry oxygen to the various organs, anemia results in lethargy, weakness, fainting and exercise intolerance.  The pet may have pale gums, jaundice and a fast heart rate.  Vomiting, diarrhea and abdominal pain may also be noted.  These signs can be seen from one day to several days after consumption of onions.  Cats are more susceptible to onion toxicity in dogs, and signs can occur with lower doses in this species.

There is no specific antidote for onion toxicity.  If your vet suspects this condition and confirms anemia, a combination of oxygen therapy, blood transfusions and intravenous fluid therapy will be used to provide support until the toxins leave the system and the body replaces the damaged red blood cells.  The pet will likely need to be hospitalized for several days and in severe cases, onion toxicity can be fatal.  Onions or food that has contained onions and related plants should never be fed to our four-legged friends and accidental feeding requires immediate veterinary attention.

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