Onions (Allium cepa) in any form are toxic to dogs---they destroy red blood cells, causing anemia. A small amount of onion can cause problems, although it can be several days before the dog exhibits symptoms. The smaller the dog, the smaller the amount of onion needed to have an adverse effect on your pet. Even very small amounts can build up over time, and the accumulation will eventually cause damage to the red blood cells.
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Anemia
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Anemia occurs when the hemoglobin level in red blood cells falls to a low level. Hemoglobin is responsible for delivering oxygen to cells and organ tissue and is essential for good health. Onions contain a substance called thiosulphate that dogs are unable to digest. Thiosulphate causes hemoglobin to oxidize and form into clumps (called Heinz-bodies). These clumps break down the red blood cell membrane structure and, ultimately, the cells die. As the red blood cell count lowers, a dog develops anemia. With a low level of red blood cells, the amount of hemoglobin present is insufficient to supply the oxygen needed by the body organs, and death can follow.
Symptoms
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The symptoms of onion poisoning are common to many other ailments, so you might need to take your dog to the veterinarian to get an accurate diagnosis. Symptoms of onion poisoning include diarrhea, vomiting, blood in the urine, yellow eyes or gums (jaundice), increased respiratory rate and pale gums.
If you notice diarrhea, bloody urine or vomiting, check your dog's gums. Healthy gums will be bright pink or red. If they are very pale or bluish, there is a problem with the blood supply. There are a number of causes of this condition, but all of them require veterinary intervention.
Foods to Avoid
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Onions are dangerous to dogs whether they are raw, cooked or processed. In most cases, a dog is not going to eat a whole raw onion, but it can get onion through eating a prepared food. Onions are present in numerous foods intended for human consumption, including spaghetti sauces, pizza, hamburgers, stews, gravy, hush puppies and meal leftovers. It is never a good idea to feed a dog table scraps to avoid potential onion consumption.
It is sometimes recommended that dogs that are reluctant to eat are tempted with prepared baby foods. If this is the case, check the ingredients, as they may contain onions.
Treatment
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There is no specific treatment for onion poisoning; the veterinarian will follow the same steps for any ingested toxic substance. These will usually include making the dog vomit and perhaps giving activated charcoal to prevent further absorption of the substance. He may also recommend an intravenous drip to replace body fluids and, in extreme cases, oxygen therapy. As with any poisoning, prevention is best, so exercise care when your dog is around human food. In a poisoning emergency, call the American Association of Poison Control Centers at 1-800-222-1222,
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