I belong to an online community of veterinarians that is populated with some of the top experts in various areas of veterinary medicine. They frequently share their expertise and advice. I found this topic extremely relevant to our daily practice.
Human health supplements are more popular now than ever. This has trickled into the pet market, too, especially with foods. We do have to be careful about assuming that human health supplements are safe and/or effective for pets. In some cases, they can be outright toxic. We need to be certain that what we’re giving is ok to give.
The mini-essay below is from a toxicologist who is boarded by both the human and veterinary specialties. She discusses how and why garlic and onions are on the “No” list in almost every case.
Garlic is more potent than onion; it takes about 5 g of garlic per kg of body weight to cause hemolysis in dogs. Cats are much more sensitive as they have more fragile RBCs. That sounds like a lot of garlic, and it is if you’re talking fresh garlic; but powdered garlic or onion are much more potent and more likely to cause toxicosis than fresh. Onion and garlic powder can be present in a lot of foods, but usually in very small amounts. Exceptions would be things like onion-flavored soup or gravy mixes and some baby foods, which can have considerably higher levels of onion/garlic. Cooked onions/garlic are hazardous because they are more concentrated than fresh and usually are highly flavored with what they were cooked with (e.g. liver and onions), so the animal is motivated to eat more of them. I believe the estimation for cats was less than a teaspoon of cooked liver and onions has caused clinical illness in cats. When inducing Heinz bodies for research studies, generally cats are given onion powder at the level of 1-3% of dry matter intake.
Onions/garlic are metabolized in the GI tract to highly reactive oxidative metabolites. ALL ingested garlic/onion will case some degree of hemolysis in dogs and cats–it’s only when sufficient RBCs have been damaged to alter the overall oxygen carrying capacity of the blood and/or to cause hemoglobinuria that the toxicosis becomes clinically evident.
So, does the small amount of garlic that is generally present in pet foods or yesterday’s beef stew cause RBC injury? Yes, but the level of injury is so low that clinically significant illness would not be expected. Some baby foods contain significant amounts of garlic/onion powder and can cause clinically relevant RBC injury if fed chronically to cats. I definitely do not recommend giving garlic tablets to cats or dogs because IF they have garlic in them, they will induce chronic anemia. That being said, most of the garlic tablets on the market that are labeled as “odor free” have had most/all of the organosulfoxides removed in the ‘deodorizing’ process, so would be less toxic. From a toxicity standpoint, I would say that the currently available flea control products when applied per label to the appropriate species are far safer than using garlic (which doesn’t work anyway) to control fleas or ticks.
Sharon Gwaltney-Brant DVM, PhD
Diplomate, American Board of Veterinary Toxicology
Diplomate, American Board of Toxicology