Garlic: Beneficial or Harmful to Companion Animals?

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imageSome foods suitable for humans are harmful – or even toxic – for animals. Most notable among these are:
• Avocado
• Alcohol
• Caffeine and other methylxanthines
• Chocolate
• Garlic
• Grapes and raisins
• Nuts (especially macadamia)
• Onions
• Xylitol (artifiical sweetener)

And while we would never feed our pets any amount of potentially harmful food, one “harmful” item – garlic – is included in many pet foods and supplements.

So, what is going on here? How can garlic be considered both harmful and beneficial? And, are companies that include garlic in their foods and supplements helping or hurting our pets? This apparent contradiction can confuse even the savviest pet parent.

Adding to the confusion is a recent article that was posted on a popular pet insurance company’s Web site. This article stated that even a “small amount” of garlic ingested by a pet can lead to severe poisoning – and even death.

Considering that I personally recommend several foods and supplements that list garlic among their ingredients, I want to clarify the facts regarding garlic’s potential toxicity.

What is garlic?

Garlic is a member of the Allium family, a genus of flowering plants that also includes onions, chives and leeks. Allium plants contain components called disulfides (disulfides are any chemical compound containing two sulfur atoms per molecule). Disulfides have been implicated as toxic for animals including dogs, cats and horses. N-propyl disulfide is considered the primary toxic disulfide.

Disulfides are oxidizing and can damage the animal’s red blood cells, causing them to rupture (hemolysis) and resulting in bubble-like pieces of oxidized hemoglobin on the outside of the cells called “Heinz” bodies. Since red blood cells carry oxygen to the tissues, a reduction in their numbers causes a type of anemia called Heinz body hemolytic anemia. Signs of Heinz body hemolytic anemia can take several days to appear. The earliest signs are generally GI related and include:
• Vomiting
• Diarrhea
• Abdominal pain
• Loss of appetite
• Depression
• Dehydration

Later signs resulting from the loss of red blood cells include:
• Weakness
• Lethargy
• Pale mucous membranes
• Rapid respiratory rate
• Difficulty breathing
• Rapid heart rate
• Jaundice
• Dark colored urine

Why doesn’t garlic affect people this way?
Some species are more susceptible to the oxidative effects of disulfides than others. Factors include differences in the hemoglobin structure of various species as well as differences in the enzymes – namely glucose-6-phosphate dehydrogenase – that protect against disulfides’ destructive effect on red blood cells.

Whereas humans are very resistant to disulfides (lucky for all of us who love garlic !), dogs, cats and horses are among the most susceptible species.

If garlic is potentially harmful or toxic, why is it included in some pet foods and supplements?
Given the potentially toxic effects associated with Allium, why do some pet products manufacturers use it at all? The issue is one of dosage. Unlike onions, garlic is considered safe when used in low doses. The manufacturers that do include garlic recognize its beneficial properties, which primarily derive from a compound called allicin and include:
• Broad-spectrum antibiotic
• Antioxidant
• Anti-cancer
• Cardioprotective

The bottom line

As long as your pet’s food or supplement comes from a reputable manufacturer, you can rest assured that the amount of garlic it contains is not harmful. However, never feed your pet any product where garlic is listed near the top of the ingredients list, because that typically means a larger amount is present. Also, refrain from giving your pet any “home prepared” foods made with garlic except in cases where a professional has provided a specific recipe, since there is a greater chance of feeding a harmful amount, whether in one dose or given over time.

Cats and all Japanese dog breeds, such as Akitas and Shiba Inus, are more susceptible to the toxic effects of disulfides and should not receive any amount of garlic.

W. Jean Dodds, DVM
11561 Salinaz Avenue
Garden Grove, CA 92843

Pet Poison Helpline 2011, ‘Are onions poisonous to dogs’?

Kovalkovicova, N, Sutiakova, I, Pistle, J & Sutiak, V 2009, ‘Some food toxic for pets’, Interdisciplinary Toxicology, vol. 2, no. 3, pp. 169-176.

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