Natural Fly Repellent

Advice for a horse owner wanting to try fly repellent supplements.

The American Association of Equine Practitioners offers advice for a horse owner wanting to try fly repellent supplements.


I board my horse at a facility with approximately 30 other horses. There is adequate pasture space for all and fairly good manure management. My question is, do fly repellent supplements work? I know that for larval killer, all horses must be on it.

But will the repellent (such as garlic mixes) work at all? If they do work, I would like to start my horse on them soon so he is protected for the coming fly season.


There’s no scientific research to support the use of garlic and other products (apple cider vinegar, diatomaceous earth) to repel insects, yet many people swear by these natural products and continue to use them year after year for their horses. The fact that there’s no supporting research doesn’t mean the products don’t work. It just means that, because they’re natural products that can’t be patented, no company is going to spend hundreds of thousands of dollars proving they work, only to have 20 other companies profit from their study.

There was a research paper published in 2005 evaluating the safety of garlic in horses because very high doses of the herb are known to cause a specific kind of red blood cell disorder. The research showed that horses that would voluntarily eat more than 0.25 grams of freeze-dried garlic per kilogram of their body weight, twice daily, did develop Heinz body anemia. To put this into perspective, an 1,100-pound horse would have to eat 4.4 ounces of pure garlic in two separate meals. Now, this is much more garlic than the label of any equine supplement recommends be fed, but it does show that just because something is natural doesn’t necessarily mean it is safe.

Dr. Lydia Gray

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