Q:  Thank you for your article on pet nutrition. I have a concern, however. You say that onions are dangerous for dogs, and especially cats. However, my son gives his animals garlic as a flea deterrent. Since onions and garlic are in the same family, is this dangerous? Many pet products contain garlic.

A:  We asked veterinarian, Dr. Richard Palmquist, to comment. Onions contain sulfur compounds, including N-propyl disulphide, which interfere with an enzyme in the red blood cells of cats and dogs. If given in high enough amounts, or for prolonged periods, the animals can develop hemolytic anemia and eventually die. Cats and some breeds of dogs are the most susceptible. Raw garlic, and garlic processed to retain its oil-soluble sulfur compounds, contain similar substances, including allicin, which can also damage red blood cells. The concept of using smelly garlic as a flea repellant in pet products is an interesting idea. However, the smelly part of garlic contains the sulfur compounds which have the potential to damage blood cells and cause bleeding in the gut. Aged garlic extract (Kyolic) contains primarily water-soluble garlic compounds, and is safe for animals. Although there isn’t enough garlic in most pet products to cause harm, the benefits of garlic as a flea repellant are not proven. Dr. Palmquist advises that he has never experienced a problem in healthy dogs and cats, but if there are any doubts, consult with your animal’s veterinarian.

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