Health Benefits of Feeding Garlic to Horses

As you are flipping through the pages of your newest supplement catalogue, you notice that garlic is featured as a feed-through insect deterrent.  Later that evening at the barn, you casually mention that you may try adding some garlic to Trigger’s feed.  Without knowing what hit you, an enormous debate ensues and your barn friends immediately chime in, “Garlic?  You might as well add arsenic!”  Well, here’s the low down on this controversial little bulb.

The Pros:  There are a number of horse supplements that incorporate garlic as a main ingredient for warding off insects.  The theory behind this feed-through method of bug deterrent is that the garlic changes the scent of the horse’s sweat thereby making them less attractive to blood suckers.  Anecdotal accounts from horse owners regarding the effectiveness of garlic is on deterring pesky insects range from rave reviews to “eh.”  Fans of garlic also tout additional nutritional benefits as well.

“Garlic contains many active components, including potent oil with sulphur-containing compounds (allicin, alliin, and ajoene), enzymes (allinase, peroxidase and myrosinase), glucokinins, B group vitamins, vitamin C and flavonoids, citral, geraniol, linalool, aphellandrene and B phellandrene.
Garlic also contains a wide range of trace minerals, which include copper, iron, zinc, magnesium, germanium, and selenium. The key therapeutic ingredient in garlic is alliin. Alliin is an odorless sulfur-containing chemical derived from the amino acid cysteine. Allicin is formed when alliin, a sulfur-containing amino acid, comes into contact with the enzyme alliinase when raw garlic is chopped, crushed, or chewed. Allicin is what gives garlic its antibiotic properties and is responsible for its distinct odor.
Garlic also has antioxidant properties. The antioxidants found in garlic may contribute to this effect by protecting against the cell damage caused by damaging free radicals. Antioxidants can neutralize free radicals and may reduce or even help prevent some of the damage they cause over time (Garlic for Horses, n.d.).”

The Cons:  Negative sentiments regarding the use of  garlic with horses stems from research that has linked a chemical found in onions and garlic with increased risk of anemia in cattle and horses.  “The toxic element in allium (a family of plants including both garlic and onions) is well known to be a chemical called N-propyl disulfide. By altering an enzyme present within the red blood cell, it depletes the cell of a chemical known as phosphate dehydrogenase (PD), whose job is to protect the cell from natural oxidative damage” (Hayes, 2002).  The trouble is, there has been little in the way of formal scientific study to determine if feeding a small amount of garlic over time can have the cumulative toxic effect that large doses of N-propyl disulfide does.  A 2005 study reported in the American Journal of Veterinary Research reported that over the course of 71 days, two horses who were given .25k/kg twice per day developed, “hematologic and biochemical indications of Heinz body anemia” compared to the two horses that were used as a control.  While this evidence is interesting, a study using four horses can hardly be considered conclusive.  Other studies on the topic fed horses large amounts of onions (up to four pounds per day) and discovered that over the course of weeks, anemia was present.  Again, I am not sure that this type of study correlates well to an average horse owner.

The Take Away:  First of all, don’t force feed your horse four pounds of onions every day.  Second, know that small quantities (1 teaspoon to 1 tablespoon) of garlic have been used my thousands of horse owners for years with a relatively low rate of toxicity and in some cases has been anecdotally successful in minimizing insect nuisance.  Third, over the course of time, there is the chance that feeding garlic can have a cumulative effect on your horse’s health… but no one is really sure.

My Two Cents:  It is always wise to make your own decision based on the recommendation of your veterinarian, your own research, and your knowledge of your horse.  However, for my guys, I feed garlic starting in April (1 teaspoon per day) and increase gradually (to about 1 tablespoon) until September.  As for whether or not the garlic makes a difference- the flies are as big a B-52s in the summer, so I’ll take all of the help I can get!



Garlic for Horses, (n.d.). Retrieved from

Hayes, K. (2002). The Great Debate: Feeding Garlic to Horses.   Retrieved from

Feeding Garlic to Horses: Benefits and Dangers. (n.d.).  Retrieved from

Pearson, W. et al.  (2005).  Association of maximum voluntary dietary intake of freeze-dried garlic with Heinz body anemia in horses.  American Journal of Veterinary Research.  Retrieved at

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