Allium species, including onions, garlic, leeks, and chives can be toxic to dogs in excessive amounts, or over time. Plants in this family contain organosulfur compounds which account for the distinctive odor and flavor associated with them. These compounds are metabolized into highly reactive oxidants which can damage the red blood cells (erythrocytes) of dogs, particularly certain Japanese breeds like Akitas and Shiba Inus. The oxidants bind directly to the erythrocytes, so these dog breeds are particularly at risk because of the specific chemical make-up of their red blood cells. All dogs are susceptible however, in contrast to humans whose red blood cells aren’t affected by the organosulfoxides. As the oxidant level within erythrocytes become higher than the cells’ antioxidant metabolism capacity, a condition called oxidative hemolysis results which affects oxygen transport and causes red blood cells to rupture and be destroyed. The erythrocytes will be marked by Heinz body formation, an abnormal blood cell visible upon microscopic examination of a blood smear.

Dogs with allium species toxicosis develop hemolytic anemia. Typically the onset is delayed by several days, but large doses may cause symptoms of anemia as little as one day after ingestion. Vomiting, diarrhea and gastrointestinal upset may also be present. The toxic dose is typically 15-30 grams per kilogram of the dog’s weight, or about .5% of the body weight. All types of allium species can cause this toxicity, but garlic is the most concentrated and therefore the most dangerous for dogs. Dried, powdered, and cooked products are just as toxic as those that are fresh and raw. As the condition progresses, the bone marrow will generate new red blood cells and the anemia will pass, as long as no further exposure takes place. High doses might need to be treated with a blood transfusion to avoid fatally low levels of erythrocytes.

Onions, garlic and other members of the allium family can be toxic to dogs. This is called allium species toxicosis, or onion toxicity. Signs may take several days to manifest.

These signs could indicate your dog has eaten onions or garlic.

These are the types of products you should keep away from your dog.

These are some of the causes and risk factors associated with allium species toxicity.

If you know your dog has ingested a product that contains onions or garlic this will make diagnosis easier. If the dog is already showing signs of lethargy and weakness, indicators of hemolytic anemia will likely be visible on a blood test. This can also help to indicate the severity of the problem. Urinalysis may show high levels of hemoglobin in the urine. Heinz body anemia may be visible on a blood smear examination even before there is a marked drop in red blood cells. Other signs, like a smell of onions or garlic on the breath (with recent ingestion), or vomiting and diarrhea with undigested pieces may also be an early indication that your dog has allium species toxicosis. For unknown instances of poisoning, the veterinarian may ask what foods you regularly give your dog and suggest you check the list of ingredients.

If the poisoning is still recent, vomiting may be induced and the dog may be given activated charcoal to reduce absorption in the gastrointestinal tract. The veterinarian will tell you to monitor your dog for signs of anemia over the next few days and may recommend a diet low in oxidants. If a large amount has been ingested, your dog may need to be kept in a veterinary hospital for that time period. Severely ill dogs will likely need supplemental oxygen to make up for the reduced circulation of red blood cells and a blood transfusion could be necessary to stabilize your dog until the bone marrow is able to generate enough new, healthy erythrocytes.

Dogs will likely recover from mild exposure to onions or garlic, but severe poisoning can be fatal, especially without treatment. If you know you dog has eaten an excessive amount of onions or garlic, you should take him to the veterinarian immediately even if there are no immediate signs. 

Avoiding exposure is the best way of managing the condition. If you are feeding your dog any food prepared for humans, check the list of ingredients for onions, garlic or other allium products. Even if your dog remains asymptomatic, continual low level doses will make any accidental ingestion much more serious. Put any spoiled food that contains onion or garlic products through a garbage disposal or place in a sealed trashcan. Take precautions if there are allium species growing in your garden. Dogs don’t normally like the taste of these plants, but it’s safer to keep them out of reach.

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