Is garlic safe for my dog?

Health Ingredients Nutrition

A search of the Internet to answer this question reveals a number of strong opinions, some overwhelmingly for garlic, and others overwhelmingly against the feeding of garlic. So who is right, and who is wrong?


Garlic is a member of the Allium family, which includes onions, leeks, chives and shallots, all of which contain the active compound allicin, which has been shown to be particularly beneficial to health in areas such as cardiovascular issues, as an anti-cancer agent, and as an anti-bacterial and anti-fungal agent. Allicin has also been shown to enhance insulin levels in the blood, thus being a useful adjunct to conditions such as obesity and diabetes. Allicin has also been shown to damage red blood cells by changing the cells to Heinz-bodies. Heinz-bodies are incapable of transporting oxygen, so it follows that too many Heinz bodies in the blood stream can lead to the development of haemolytic anaemia.

The argument for garlic:

Pet owners have long included garlic in the food for their dogs in an attempt to utilise the health benefits ascribed to humans, and there is plenty of anecdotal evidence to support the inclusion of therapeutic quantities of garlic in the food. Issues surrounding the cardiovascular system such as heart attack, high blood pressure and atherosclerosis can all be aided by the inclusion of garlic, as can liver detoxification and the reduction in the levels of bad cholesterol.

Most of the curative properties of garlic can be attributed to allicin, but this chemical is only found in fresh crushed garlic and quite quickly breaks down when exposed to the air. Most herbalists recommend only feeding freshly crushed whole garlic, which has been allowed to sit for 10 minutes after crushing and prior to feeding. This concentrates the amount of allicin present in the food and delivers the best curative properties of the garlic. However, allicin breaks down through exposure to the air and heat or cooking. The resultant compounds are sulphides, particularly diallyl sulphide, which retains many of the benefits of allicin, but to a lesser effect.

The major therapeutic claims attributed to garlic include:

  • Antimicrobial action – garlic is reported to possess strong antimicrobial properties that are an effective aid in controlling bacterial, fungal and viral infections. This effectiveness is commonly reported to be of most benefit to infections of the gastro-intestinal tract.
  • As a parasite deterrent – ticks and fleas have long been thought to be susceptible to the properties of garlic although the actual reasons for the repellent action are unknown. Garlic has also been reported as being effective against tapeworm infestation and also as a sterilant against some organisms such as giardia.
  • As an immune system booster – garlic has long been credited as a booster of the immune system by enhancing the white blood cell count, which is extremely important in the body’s fight against cancerous cells. It can be used either as a protectant against the development of cancerous cells, or as an aid in the treatment of various cancers, particularly colon cancer.
  • As a detoxifier – garlic is also reported to enhance liver function, thus assisting in the elimination of toxins from the body.
  • As an aid to cardiovascular health – allicin in the food can also help lower cholesterol levels, particularly in those breeds that are susceptible to hyperlipidaemia such as Miniature Schnauzers, Shetland Sheepdogs, Rough Collies, Dobermans and Rottweilers (whilst not all animals within these breeds suffer from the problem, hyperlipidaemia is often a genetic condition found in some families). The treatment of atherosclerosis is also effected through the reduction of the blood lipid level.

Whilst most of the beneficial effects of garlic are attributed to the action of allicin from fresh whole garlic, the same effects but to a lesser extent are also attributed to the inclusion of dried garlic in the diet, particularly due to the presence of diallyl sulphide, which has been shown to be extremely useful in the control and treatment of colon cancer, as an anti-microbial, and as a repellent against worms and fleas. However, most holistic treatment methods warn against feeding too much garlic from these sources, particularly garlic powder and minced garlic. Garlic powder is rarely pure; it is usually cut with other powders to reduce the problems of caking. Consequently, this reduces ones ability to accurately assess the dose rate being fed unless of course the actual purity is known. A far safer method is to only add pure dried garlic chips to the food, whereby a far more accurate dosage can be calculated.

The argument against garlic:

Many canine health advocates are strongly against the inclusion of garlic in your dog’s diet. The reason for this opposition relates to the strongly held belief in some quarters as to the potential damage that can be caused to the animal’s red blood cells. This is due to the active components of garlic in that the herb contains quite large concentrations of organosulphoxides, with some of these organosulphur compounds being sufficiently oxidative in action to overwhelm the body’s antioxidant capability.

This effect was the subject of investigative work conducted at Hokkaido University in November 2000. In that experiment, four healthy mixed breed dogs were fed 1.25ml of garlic extract per kilogram of bodyweight for seven days. This equates to 5g of whole garlic per kilogram bodyweight per day, which means a 20kg dog was fed the equivalent of 100g of fresh garlic per day. Another four healthy mixed breed dogs were fed water instead of the garlic extract so as to provide a control group. All animals were comprehensively blood tested every day from the onset of the trial for 30 days. The test group were found to have damaged blood cells including Heinz-bodies, with the concentration of damage peaking at days 9 to 11 from the onset of the feeding. There was no damage to the blood cells in the control group. Consequently, it was concluded that garlic extracts have the potential to cause oxidative damage to the erythrocyte membranes in dogs, thus putting them at risk of haemolytic anaemia, although none of the test group showed actual symptoms of anaemia.

This is supported by the knowledge that the dog’s antioxidant ability for the protection of erythrocyte membranes is quite low, so the overwhelming of the body’s antioxidant protection by the organosulfur compounds was not unexpected. Furthermore, the antioxidant capacity in cats is even lower than dogs, thus making cats even more susceptible to this type of anaemia if exposed to garlic or other members of the Allium family. Since the results of the Hokkaido trial were published, additional research has been conducted in an attempt to identify the actual chemical in the garlic that is responsible for the damage to the red blood cells. That investigative work is on going.

So who is right and who is wrong?

Well, there is no doubt there are rights and wrongs on both sides of the argument. The pro-garlic advocates point to the extremely high dose rate of garlic extract fed to the trial dogs, whilst the anti-garlic advocates claim that any erythrocyte damage is bad regardless of how much or how little damage has occurred at any one time. And indeed, much of this debate is very much at the core of the larger debate surrounding the subject of food as medicine.

There are many examples in nutrition whereby some compounds are good when fed at the correct or therapeutic level, but harmful when fed to excess. In fact, for some nutrients the dilemma is far greater in that the absence of the potentially toxic substance can lead to malnutrition and death. One such example of this is the mineral selenium, which plays an essential role in cellular function in most animals including our dogs and cats. However, in larger doses selenium is toxic. This same situation also exists with many of the other essential minerals, and some vitamins as well.

The consensus amongst canine nutritionists is the benefits of low doses of garlic actually outweigh any disadvantages the herb may possess. The common belief is that garlic is a natural antibiotic that doesn’t affect beneficial gut bacteria, helps the liver rid the body of toxins, destroys cancer cells and boosts the immune system (particularly important where allergies are present), lowers cholesterol and triglycerides, plus acts as an anti-viral and anti-fungal agent in the body. But, without doubt the largest consideration of all is the size of the dose rate. For therapeutic benefit the generally accepted dosage is approximately 1 clove daily per 20kg body weight. Some advocates actually quote a higher dosage, whilst others talk of only feeding intermittently (week on then week off, or similar).

Our experience at LifeWise gained over many years of research and the controlled feeding of garlic is that modest levels of garlic provide more benefits to health and wellbeing than not feeding garlic. However, there are circumstances where all parties to the debate agree that garlic should not be fed. Perhaps the single most important consideration is with young pups, in that puppies don’t actually produce new red blood cells until after six to eight weeks of age. Some breeds, such as Akitas and Shiba Inus appear to have a genetic predisposition to being more sensitive to the hemolytic effects of N-propyl disulphide, and shouldn’t be fed garlic either. Other excluded groups would include any animals suffering from anemia, diabetic dogs, or animals scheduled for surgery. It is also generally accepted that dogs with autoimmune disorders should avoid garlic.

Hopefully this has shed some light on the controversy. Should you require additional information please leave a question on the contact form below. Alternatively, please feel free to join the discussion.

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