Onions and Dogs: A Lethal Combination

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stockxpertcom_id443176_jpg_dcc1d55eaedb6fb1b0436e12b41913a6Sophia Yin, DVM September 4, 2009


While many of you already know that chocolate can make your cat or dog sick, did you know that onions can kill? I learned this my second year in veterinary school. But I didn't really appreciate it until the big onion incident that occurred during my senior year. Well, maybe the incident wasn't all that big; it only involved one dog. But it was my own dog, Max, a 72-pound adult Boxer. And it nearly killed him.

Not surprisingly, pets actually have to eat the onions to get sick, but depending on their size, they may not have to eat much. One fourth of a cup can make a 20-pound dog sick while several cups may be needed to make a large dog sick. Cats are even more sensitive.

You're probably asking yourself, “What dog or cat with brains would eat onions?” Well, the onions don't have to be raw. They can be fried as in onion rings, dehydrated, as in Lipton Soup, or prepared in some other tasty form such as sautéed with mushrooms and steak, or hidden in a souffle. In a scattered rash of cat onion toxicity cases a number of years back, the culprit was onion powder used to flavor some baby foods. Veterinarians often temporarily feed meat baby food to cats who are infirmed and unwilling to eat their regular foods. So when the baby food formulations changed, some cats took a turn for the worse while under veterinary care. Due to public pressure baby foods no longer contain onion powder.

In Max's case, the onions were fried, dried and then left on the coffee table by my roommate before she left for the weekend. I never saw the pound or so of deadly cuisine. All I found was an empty bag and drool on the floor. If I had known what was in the bag, I would have taken Max to my veterinarian immediately. Instead I took him two days later, after the normally boisterous prankster collapsed while exercising. We performed a bunch of diagnostic tests, and on examining the blood work, found the tell-tale signs—little purple clumps in his red blood cells that virtually screamed onion toxicity.

Onions cause toxicity by oxidizing an oxygen-transporting protein called hemoglobin in the red blood cells. When oxidized, hemoglobin forms clumps which can't carry oxygen as well. These small clumps, called Heinz bodies can be seen in the red blood cells when the blood is viewed under a microscope, especially when the cells are stained with a special stain called New Methylene Blue. Although a number of other compounds can cause Heinz bodies, when a veterinarian sees Heinz bodies in many cat or dog red blood cells, onion toxicity is the first differential that leaps out on the list. Normally, in dogs with onion toxicity a moderate number of red blood cells may contain Heinz bodies. In Max's case, most of the red blood cells carried the protein clumps.

Heinz bodies don't usually cause life-threatening problems themselves; the red blood cells can still carry oxygen, just not as efficiently. Heinz bodies cause problems by decreasing the red blood cell lifespan. As a result, the onion-eater becomes anemic. If a large amount of onions is eaten at one time, the pet may develop a sudden anemia several days following the onion feast. If the dog or cat eats a small amount of onions every day for many days, he may gradually develop anemia over weeks to months.

Onion toxicosis is not a tremendously common occurrence. Annually, the ASPCA National Animal Poison Control Center in Urbana Illinois records only a handful to a dozen calls on onion toxicity and toxicity from its relatives in the Allium genus, garlic and chives. Probably because with low dose exposure, pets may not develop signs severe enough to take to a veterinarian or at least not sick enough to perform diagnostic bloodwork for a definitive diagnosis.

It's a good thing the incidence is relatively low, since patients that do eat enough onions to develop toxicosis often need to be hospitalized for several days. In cases of severe anemia, they may even need a life-saving blood transfusion. Max did. Luckily most victims of onion over-ingestion respond well to treatment and recover.

Interestingly, garlic can cause the same problems as onions, but since garlic is usually only used in small amounts, dogs and cats aren't likely to ingest a toxic quantity.

The signs you see with onion toxicosis are signs of anemia and low oxygen such as lethargy, weakness, red urine, decreased stamina, and pale or bluish gums, especially with exercise. While onion toxicity is not a common cause of these signs, consider onion toxicosis if you see these signs and know your pet has gotten into onions recently. If by some freak occurrence, your dog or cat does engage in an onion feast, take him to your veterinarian immediately. She may induce vomiting or administer a product to help decrease the absorption of the onions. If you take this trip in time, your onion eater may be spared many or all of the hazardous sequelae of onion toxicosis and you may be spared the much larger bill associated with intense hospital monitoring and a several night stay.

Footnote: other human foods to avoid include moldy walnuts, grapes or raisins, chocolate, fatty foods.

For more information on the ASPCA National Animal Poison Control Center, go to http://www.aspca.org/pet-care/poison-control/. To consult with a veterinarian at the Center's emergency hotline for a $60.00 fee call (888) 426-4435.


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34 responses to “Onions and Dogs: A Lethal Combination

  1. Wow, I never knew this information. I did know about grapes and chocolate, but not onions. It’s amazing how many people don’t know any of this. I feel they should give a small booklet at the vet containing information such as this. I’m sure some do, but I have never received anything. Although my wife and I did our homework before we got our baby.

    1. When I first got my Siberian Husky I thought he would be able to handle onions and grapes but he did eat a big piece of chocolate the other day nothing happen I thought he could eat grapes but I never tryed to give them to him today he ate a little piece of onion on a burger he jumped up on the counter and ate it I looked on this website to see if a little piece of onion could hurt him but he seems to be fine.

  2. Good thing that I ran into your website. I was pretty close to give my dogs some leftover fried onion rings they seemed to be interested in. Thank you. You saved us a lot of trouble!

  3. My rat terrier is not doing so well right now, and she is old. I noticed something was off when she started yelping while laying on the couch and then she jumped off and came toward me, still yelping. She seemed to be fine after that but a couple hours later when we went to leave the house she was walking weird to the car, going sideways with stiff legs. Since then she has not been able to walk or even stand on her own and I can’t afford to take her to the vet right now. I don’t know what’s wrong with her and it kills me seeing my baby go through this. I was curious if anyone knows what it could be that’s causing this

    1. If your pet is having a medical issue, we recommend you go to a vet. We cannot provide medical diagnosis or referrals over the internet. You may want to search for animal care clinics, rescue organizations or humane society offices in your area. We hope that your terrier gets better soon.

    2. Sounds like a pinched nerve in her back, or maybe a slight stroke? DEFINITELY want to involve the vet at this point. Good luck and God Bless.

  4. I have a 3 months old puppy who weighs about 3.5 pounds. Yesterday, while i was chopping onions, he took a very a chopped piece of onion and ate half of it. Should i be concerned?

    1. We cannot answer medical questions on a blog, because it requires a doctor looking at your puppy. If there are any medical concerns, you should take your pet to the vet.

  5. I’ve been putting organic chicken broth on my dogs dry food. She loves it. Now I notice it is made with onions. Could this small amount in broth harm my dog? She a 70 pound lab. I haven’t notice any symptoms. Should I just stop giving it to her.

    1. Dawn,
      I was doing the same with my 66 lb husky mix. I stopped after I learned onions were bad for them and the broth contained then. What I do now is make my own broth whenever we eat chicken for dinner. I just save all the bones and boil them with cut up celery and carrots. After 10 mins or so I remove the bone and put the broth in mason jars along with the carrots and celery. He loves it!

  6. If my dog eats onions, should i just watch him to see signs of toxicity or should I make him throw up or something, the article does not say.

  7. Hello, my 3 pound puppy ate human vomit that contained some onion, she is now having a dry hacking cough. It is sunday and her vet clinic is closed. What should I do?

  8. My french poodle would sometimes eat cooked onion slices and not a thing EVER happened to him. Of course, years later I found out that onions can be lethal to dogs and have since stopped giving onions to my dog. He’s still alive & kicking Ativan 13 years of age.

  9. Hi All ,
    Sharing such informations is really beneficial , but i want to add that , my dogs are almost 4 months now , i always cook freshh food daily , concentrating on boiling the sewdust to the max almost 2 hrs and always with 3 shopped onions , i thought that it would help killing any bacteri , and i see no side effects at all , the breeds are healthy strong , hiper name it …
    No vomits , dearia , or etc…
    My question is if that is ok because they are used on it since i purchased at the age of 2 months ??
    Or something is happening at the back seen of their organism and it will appear later ?

    1. I’ve been reading a lot about this and everything that I have found says to stop feeding them immediately. It sometimes isn’t a quick reaction it could develop over time and give them issues later on. I’m also not an expert but I’d suggest to not feed them it anymore. I wouldn’t chance it.

    2. Some dogs, if they were autonomous, might very well choose to eat onions and be at risk for anemia, the bad things that anemia causes, and a shorter, less comfortable, short of breath quality of life.

      My vet told me to limit my cat’s food, stating “you’ll get a few more years out of them.” If Kitty was autonomous, and I asked her if she’d rather be fed, fat, and happy for 15 years, or if she’d prefer a hungry, boring, unhappy life for 17 years, she’d say, “gimme the food.”

      I think that the risks versus benefits points to a clear choice to discontinue the onion feedings. Unless your dog could make the choice to eat onions and be short of breath and fatigued, you just should err on the side of safely.

      If you feed your dog onions, and it builds up slowly, can you stop the damage in time to reverse it well enough that other systems are not permanently impacted in a negative way?

      If you stop feeding your dog onions, will he perceive this as a slight? Keeping him out of the circle? Will he be unhappy eating his food without onions in the gravy?

      My dog loves to eat. But, if I laid out two bowls of gravy, one with onion and the other without, I’m not convinced she wouldn’t just eat them both without noticing or caring about the presence of onions.

      So, feed onions for real potential for harm, or withhold and have the pup hate you for it? Will he ever let it go and forgive you for it? Or, would he just eat the onion less gravy and be happy he has gravy?

  10. It sounds from this article like cooked onions also cause problems? Some dog treats contain onion powder. I will not feed my dogs these treats, but someone told me as long as the onions are cooked it’s okay. I had not heard that before and can’t find anything online. Would love your input!

  11. I hv been feeding leftover with lots of onions and garlic. My 12yr old dog hv been consuming the cooked onions n garlic happily.

    1. Damien, PLEASE stop feeding these! The liver or kidneys can be affected too- not necessarily immediate. The article is FACTUAL- your dog WILL be affected and you are shortening his life! Please?

  12. Interesting, I’ll stop feeding them to my dog.

    However, the grapes thing is news to all the winery dogs I know, as they almost invariably eat the grapes when ripe. Maybe they don’t understand the deadly nature of their food of choice.

  13. Thank you so much for this information our boxadore who is 10 mths old was given about 3 tablespoons with a mix of cooked hamburger, rice and oinions. I used a half of an onion with about 2.5-3 pounds of hamburger. and 3 cups of rice all was put into green peppers and cooked on top of the stove in tomato soup,, It just happened what should I do.?! It’s Saturday night and it’s after 11:00 pm. We will never do this again.

  14. Can a dog eat a beef stew that onions are cooked in if you only give them the meat and carrots and potatoes?

    1. Anything like this can be risky as it’s not the physical onion itself but the chemicals in the onion that end up in the stew. Theoretically, you should be ok but smaller dogs can have issues, there is no way to know how much onion ends up in the finished product and there are just some dogs that have bad reactions.

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