Feeding Dogs Garlic and OnionAccording to the American Kennel Association, all parts of the onion plant are toxic to dogs. Raw or cooked, fried or powdered, onions and the rest of the allium family are harmful to dogs. N-propyl disulfide causes a breakdown of red blood cells, leading to anemia in dogs. Some owners feed their pets small amounts with no apparent harm. This is a page about feeding dogs garlic and onion.