Visiting Veterinarian

Hold the spices, please

By Michele Gerhard Jasny V.M.D. - February 1, 2007

An Island veterinarian recently stopped into a local establishment for a caffeine fix. Along with the yummy baked goods for people, the shop sells homemade dog treats and the doctor in question purchased one for her own pup. During the transaction, a conversation ensued. The baker happily listed the tasty stuff that went into these delectable dog biscuits. It all sounded nutritious and healthy until the baker mentioned that the biscuits contained onion and garlic powder. "Oh no," the veterinarian said. "Do you know that garlic and onions can be toxic to pets?" A little while later, that veterinarian gave me a call and suggested I write an article to better inform the public about how, in certain circumstances, these seemingly innocuous flavorings can be a danger to our pets. Good idea, doc. Here it is.

Garlic and onions belong to the Allium species, along with leeks, chives, shallots, and scallions. For thousands of years, people have used these aromatic plants for food and medicinal purposes. The idea that they might somehow be poisonous seems counterintuitive. This is the moment when you get to understand how a veterinarian is different from a human physician. I bet your physician doesn't know how cat red blood cells are different from dog red blood cells are different from human red blood cells. (Okay, honestly, I had to look it up to remember the details.) All of us have hemoglobin in our red blood cells (RBCs) but the chemical composition is different. Cats have eight sulfhydryl groups on their hemoglobin. Dogs only have four sulfhydryl groups on theirs. People have two.

Why should you care about this bit of biochemical trivia? Because garlic and onions contain substances that cause oxidative damage to RBCs by interacting with the sulfhydryl groups. The more sulfhydryl groups, the greater the risk of oxidative damage. And why should you care about oxidative damage? Because it can lead to destruction of red blood cells. If a dog or cat eats a sufficient quantity of onions or garlic, he may get an upset tummy and vomit within 12 hours. More seriously, changes can occur in the blood two to five days later. If enough RBCs are destroyed, he may exhibit discolored urine, weakness and pallor, due to a condition called hemolytic anemia which is potentially life-threatening.

Is a tiny bit toxic?

So what do you do if Vidalia, the Vizla, eats the onion rings or Scampi the cat chews on the chives? Is a tiny bit toxic, or do they need to overindulge before it becomes a problem? If this stuff is dangerous to pets, how come every dog who gets a homemade biscuit doesn't keel over?

Although Allium toxicity is a real concern, we do not see cases very often. Raw onion, in general, is not too attractive a treat to pets. Garlic may be tastier (and more toxic than onions ounce-for-ounce), but it's is less likely to be lying around the kitchen in large enough quantities to be dangerous. How much is too much? There is little precise data available. For onions, the current published toxic dose for dogs is 0.5% of the animal's body weight. I bet you'd like me to translate that for you into number of onions per pet. One half of one percent of 50 pounds of Vizla is a quarter of a pound, right? ( .005 X 50 lbs. = 0.25 lbs. ) This means that if a 50-pound pup eats a quarter pound of onions (about two medium onions) that's enough to possibly cause hemolytic anemia. What about Scampi the cat? If she weighs one quarter of what Vidalia weighs, by this formula, a mere half of a small onion may be toxic to her. And cats are more susceptible than dogs to Allium toxicity.

For garlic, five grams of whole cloves per kilogram body weight is considered risky to dogs. Five grams is about one teaspoon is about one clove. Vidalia would need to eat twenty-three cloves of garlic. As you can see, the risk to medium to large dogs is relatively low. Even a small cat like Scampi probably won't like raw garlic enough to eat a toxic portion.

Where we can get into trouble is when we combine concentrated materials with small patients. Scampi might not eat half a raw onion, but might lick up the dregs of that beef stew you made that's chock full of sautéed onions. A little dog might not bother with a raw bulb of garlic, but might devour that jar of minced garlic in olive oil you inadvertently left open within reach. How about that box of dried onion soup mix? Or the garlic or onion powder? Drying and grinding does not lessen the toxicity, and these products may be hidden in places you wouldn't think of. There are reported cases of cats developing hemolytic anemia from eating baby food flavored with onion powder.

So what do you do if Scampi slurps the onion soup, or Vidalia gulps the garlic bread? Talk to your veterinarian first to determine if the quantity ingested was large enough to be worrisome. If ingestion was recent, treatment may begin with inducing vomiting. In dogs, you can generally do this by giving them hydrogen peroxide orally at home. Using peroxide in cats is controversial; many vets, myself included, believe it is too irritating for kitties and can do more harm than good. Check with your veterinarian before inducing vomiting in either species. After that, administration of activated charcoal may help minimize absorption of toxins. Some veterinarians advise giving cats Vitamin C. Then it's wait and see, and monitor Scampi's blood. If hemolytic anemia develops, whole blood transfusions and intravenous fluids may be needed.

Allium alert

Who'da thunk it? Onions and garlic dangerous? The reality is that for many years people have given garlic to their pets as dewormer and flea control. Some still do. People sprinkled garlic and onion powder on ailing pets' food to entice them to eat. Some still do. In most cases, the amount of Allium species compared to the size of the animal is not sufficient to cause a clinical problem. On the other hand, the garlic probably doesn't really control worms or fleas, and there are safer ways to spice up dinner. And in some cases, owners cause serious harm.

Many foods can be problematic in the right circumstances. There are reports of macadamia nuts causing muscular weakness and tremors in dogs. Avocado can be deadly to birds. Cows can get sick if they graze repeatedly on kale or turnip greens and sheep fed too much cabbage can have reduced productivity. If a dog eats raw bread dough, his body heat can make the dough rise and ferment causing all kinds of troubles.

Here's the take-home message. If you're at the pet store, bakery, grocery store, or coffee shop and you see some homemade dog biscuits, check the ingredients list. You might want to eschew any containing garlic and onions, especially if your dog is a little guy. Some Japanese breeds, even though they are larger, are more prone to Allium toxicity, including the Akita, Shiba, and Tosa. Remember that, across the board, for both onions and garlic, cats are more susceptible than dogs. Skip the baby food with onion powder. If you give table scraps to your pet, avoid anything made with Allium species, especially to a cat or small dog. A dash may not be harmful, but why borrow trouble? Scampi will be just as happy with her treats sans onions. And Vidalia's doggie breath is bad enough without the garlic.