The Risks of Garlic for Horses

Understanding Garlic Use in Equine Diets

• There are many old wives’ tales about garlic, and we need to balance that with effectiveness and safety. It is related to onions, which are a known toxin for horses. For the most part, garlic for horses may not be unsafe in small, controlled portions. However, it’s not always clear at what dosage, or form, makes garlic toxic. There is also mounting evidence that feeding it over a long period of time, even in moderation, is unwise.

• There are numerous anecdotal stories about garlic and horses, including its use for fly control, immune system support, respiratory health, and as a natural dewormer for intestinal parasites.

• Garlic for horses can be powdered, pelleted, flaked, raw, or in oil form. The strong taste and aroma vary between forms, and you may find your horse doesn’t want anything to do with it.

Nutritional Components of Garlic Beyond Allicin

• Allicin is the portion of garlic responsible for the taste and smell, and many believe it’s the key to garlic’s usefulness, especially for fly control. Garlic also has vitamins, minerals, and other potent sulfur compounds besides allicin.

• Garlic contains B vitamins, vitamin C, selenium, iron, calcium, and phosphorus, in addition to allicin.

• Pound for pound, garlic is nutritionally dense! But you would need to feed pounds and pounds of it to make a dent in a horse’s nutritional requirements. So for horses, it’s nutritionally poor.

The Science Behind Feeding Garlic for Horses

• There is considerable scientific evidence that garlic can trigger anemia in horses. Some studies have shown that even small doses, fed over time, have the same effect as larger doses in shorter time periods. Most of these studies agree upon the need for more research, especially into the effectiveness against flies and insects.

Antibiotic Uses

• There is evidence that garlic acts like an antibiotic in some cases. However, most studies involve a laboratory, and not a living being. One research paper notes this:

Allicin, one of the active principles of freshly crushed garlic homogenates, has a variety of antimicrobial activities. Allicin in its pure form was found to exhibit i) antibacterial activity against a wide range of Gram-negative and Gram-positive bacteria, including multidrug-resistant enterotoxicogenic strains of Escherichia coli; ii) antifungal activity, particularly against Candida albicans; iii) antiparasitic activity, including some major human intestinal protozoan parasites such as Entamoeba histolytica and Giardia lamblia; and iv) antiviral activity.

• This paper has nothing to do with horses. At all. Which is part of the trouble – we don’t know if these discoveries in labs and other living creatures translate to horses. And if they do, what’s the dose, and will it cause dangerous anemia?

Read more here.

Ingested Garlic vs. Topical Garlic as an Antibiotic

• When one eats garlic, the digestive system maze and digestive acids quickly turn allicin into smaller sulfur compounds. There is little chance that the antibiotic properties of allicin reach any intended target. And what about unintended targets?

• For topical garlic uses, it can be irritating, causing more problems than solutions. The last thing a wound or insect bite needs is a layer of contact dermatitis complicating the healing process.

Dosing Garlic for Horses – Freeze-Dried Garlic and Anemia

• This study found that these horses will voluntarily eat enough garlic to develop anemia. A daily dose of 0.2 grams of garlic per kg of body weight equals 3.2 ounces of garlic for a 1,000 lb. horse.

At a daily dose of > 0.2 g/kg, horses fed garlic developed hematologic and biochemical indications of Heinz body anemia, as characterized by increases in Heinz body score (HBS), mean corpuscular volume (MCV), mean corpuscular hemoglobin, platelet count, and serum unconjugated and total bilirubin concentrations and decreases in RBC count, blood hemoglobin concentration, mean corpuscular hemoglobin concentration, and serum haptoglobin concentration. Recovery from anemia was largely complete within 5 weeks after termination of dietary supplementation with garlic. Heinz body score and MCV remained high at the end of the 5-week recovery period.

Read this summary here.

Respiratory Benefits and Long-Term Use at Lower Dosages

• Science does confirm that garlic can benefit respiratory health. This news is fantastic, as many horses struggle with heaves and other respiratory disorders.

• In one study, horses received 16g of garlic powder per day for over 80 days. This equals about .57 ounces, much lower than the 3.2 ounces thought to be “safe” for horses.

• While the horses did show signs of improved respiratory health, they also showed signs of anemia despite receiving such a small dose. This suggests that long-term use of garlic at small doses can influence a horse’s health negatively.

Read more about this research here.

More Research about Low Doses Over Time

• Another researcher examined the in vitro and in vivo uses of garlic for horses, drawing a few conclusions. One example is garlic, which, as an antibiotic for the common Streptococcus equi bacteria, requires dangerously high dosages.

• Another finding was that horses receiving low doses over time may be in danger, as the fatty tissues in horses store the garlic metabolites. This fact does not bode well for using garlic at all.

Horses are capable of consuming sufficient quantities of dietary garlic to induce toxic effects. However, the current research cannot definitively define a toxic dose. It is likely that the safe dose of garlic will be dependent on duration of exposure, as it is known that garlic metabolites are lipophilic, and as such tend to accumulate in fatty tissue, slowing their excretion from the body (Germain et al., 2002). This suggests that low doses of garlic will likely persist in the tissue, and a toxic threshold may eventually be exceeded even at low doses. The maximum safe acute and chronic dose must therefore be established in a species-specific manner to account for potential inter-species differences in bioactivation and biotransformation.

Read the paper here.

Fresh and Crushed Garlic and Garlic Flakes as Dewormers

• You may have heard that garlic for horses is fantastic as a dewormer. Well, science says otherwise. Researchers gave groups of horses different types of garlic (fresh, crushed, and flaked), and no group showed a reduction in egg shedding.

 In equine practice, there is a traditional use to treat horses that are affected by internal parasites with garlic, but our study showed that this common practice has no effect on reducing the strongyle egg shedding.

Read this research here.

Garlic as Fly Control for Horses

• The internet is filled with testimonials about feeding garlic to horses as a fly repellent – but there’s no research (yet) about this in horses.

• One review examined the use of garlic supplements in cattle, finding potential applications in the cattle industry. However, this study is preliminary and did not exclude genetic factors. It’s important to remember that horses and cows will not react the same to everything they ingest.

You can read the review here.

• Another article by an equine nutritionist weighs the potential for fly control with the known risk factors of anemia. Her conclusion is to skip it and look to other solutions to repel pests.

While many people feed garlic and report no ill effects, the clinical signs might not be obvious and depending on the dose, frequency, and duration of the dose given there could be low-grade deleterious effects.

Read the article here.

Risks and Side Effects of Garlic for Horses

• It’s easy to forget that “natural” does not equal harmless in many cases. We know that feeding supplements are unregulated, and we also know that garlic isn’t great for horses.

Concerns About Heinz Body Anemia and Blood Health

• The disulfides in garlic for horses create oxidative damage to the hemoglobin inside red blood cells. The triggers the creation of Heinz bodies, which are promptly removed from the bloodstream, resulting in anemia.

• Anemia is characterized by a lower number of red blood cells, called erythrocytes, or hemoglobin, the protein in red blood cells that carries oxygen. With this sub-optimal level of oxygen-carrying cells, the body can’t deliver sufficient oxygen to the organs and tissues.

• Garlic-induced anemia can occur in as little as 10 days. However, reducing the dosage to an assumed “safe” level can create anemia when fed for about 80 days. The risk increases as the dose and duration increase.

Signs of anaemia in horses

Horses developing anemia don’t suddenly appear anemic. You may see vague signs, such as:

• Lethargy or general weakness. Your horse may resist exercise, show a lack of energy, and appear depressed.
• They may have declining performance, and you may feel like they are losing fitness.
• You notice elevated resting heart rates and respiratory rates as their bodies struggle to deliver oxygen to cells. This is another excellent reason to check your horse’s vital signs daily.
• Jaundice is a possibility, and you may notice yellowish eyes and gums.
• Your horse’s appetite will decrease.
• Their hair coat looks dull and lifeless.
• Any abnormal behaviors and lackluster attitude should be shared with your vet. Countless things could resemble anemia. Bloodwork is a great place to start!

When deciding what to feed your horse, the best thing you can do is work with an equine nutritionist and vet to weigh the known risks against the unknown benefits. If you are concerned primarily with fly control, there are many other safe and effective alternatives to a garlic supplement. For respiratory health, this is a discussion to have with your veterinarian. Modern veterinary medicine can work wonders for your equine partner without risking anemia.

Key Highlights

Here are the key takeaways about using garlic in your horse’s diet:

• Many perceived health benefits of garlic, like immune support and insect control, lack strong scientific backing.
• Garlic is available in various forms, including garlic powder and raw cloves, but its active compounds vary with processing.
• A significant risk associated with feeding garlic is Heinz body anemia, a condition that destroys red blood cells.
• Even small doses of garlic given over a long period can be harmful to your horse’s health.
• Always consult a veterinarian before adding garlic products to your horse’s diet to ensure safety and proper dosage.