GARLIC CAN BE DEADLY
It has long been thought that garlic provides many health benefits when fed regularly to our pets. Garlic has been shown to stimulate white blood cells, prevent tumor formation, and decrease blood cholesterol. Vets have proposed garlic as a treatment for allergies, asthma, diabetes, heart disease, cancer, infections, intestinal parasites, and kidney disease. Add to these its effectiveness as a natural flea and parasite repellent and you would naturally be inclined to include it in your pet’s diet. Many manufacturers of raw and other natural diets include garlic in their formulas. Most treats and vitamins contain garlic. You can even buy supplements made of 100% garlic. Until recently, garlic was thought to be an inexpensive, natural, and safe way to fight parasites and improve the health of our pets.
Garlic is part of the onion family (alliaceae) along with leeks and shallots. There is ample research available which indicates onions can be harmful, if not deadly, to our pets. In the last five years, more and more toxicity studies are being conducted on garlic and all seem to indicate that it, too, can pose serious health risks when fed to cats and dogs. A 2003 study on Grape and Raisin Toxicity in Dogs, published in the Australian Veterinary Journal begins, “The list of commonly available human foods toxic to dogs continues to grow. Grapes and raisins can be added to onions, garlic, chocolate, and macadamia nuts as posing dangers when ingested in excessive quantities.”  Unfortunately, no one knows what constitutes “excessive quantities.” In an article on Onion and Garlic Toxicity in Dogs and Cats, Jennifer Prince, DVM states: “Garlic and onion are used as flavor enhancers in food. Since the toxic amount is unknown, it is recommended not to add it to your pet’s food. These ingredients can cause Heinz body anemia, resulting in a breakdown of the red blood cells and anemia (hemolitic anemia).”  Although the exact toxic dose is not known, studies unanimously agree that foods containing garlic should not be fed to dogs.
I have spoken with owners who have been feeding garlic to their dogs for years with no apparent ill effects. They maintain that, until something better is found to fight fleas, they will continue to feed garlic. Once again, it seems that we are far too willing to subject our pets to potentially dangerous substances in the name of convenience. If someone told you that feeding your dog arsenic would keep him from getting fleas, would you consider doing it? Of course not. The effects of garlic toxicity are not inconsequential. They include vomiting, diarrhea, anemia, tachycardia [irregular heart beat] weakness, liver damage, allergic reactions, asthmatic attacks, contact dermatitis, and gastrointestinal damage. [2,4,5]
There are many forms of garlic—fresh raw, cooked, dried, oil of garlic—all of which pose the same serious risks when fed to dogs and cats. Jennifer Prince DVM states that “The bulbs, bulbets, flowers, and stems of the garlic and onion are all poisonous” and that “both fresh and dried (for use as spices) are equally dangerous.”  In a paper titled: Toxin exposures in dogs and cats: Pesticides and Biotoxins, Michael J. Murphy, DVM, PhD, writes: “The active ingredient in oil of onion is allyl propyl disulfide; the active ingredient in oil of garlic is a similar compound called allicin. Garlic may cause contact dermatitis or imitate an asthmatic attack.”  A 2001 study on the effect of garlic on the gastrointestinal mucosa compared the effects of several different forms of garlic on the lining of the stomach and intestines. The results of the study showed that the dehydrated boiled garlic powder caused “severe damage” to the lining of the stomach; the dehydrated raw garlic powder caused some reddening, and that the aged garlic extract had no ill effects on the stomach membranes. The study also found that feeding enteric-coated garlic tablets caused “loss of epithelial cells at the top of crypts in the ileum.” 
To read the full article by Laura Murphy, click on the link below.
Pets By Nature