Onion in all forms -- powdered, raw, cooked, or dehydrated -- can break down a cat's red blood cells, leading to anemia. That's true even for the onion powder that's found in some baby foods. An occasional small dose probably won't hurt. But eating a large quantity once or eating smaller amounts regularly can cause onion poisoning. Along with onions, garlic and chives can cause gastrointestinal upset.
