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Do fly control supplements really work?


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 kind like garlic mixes work at all? And if they do work I would like to start my horse on them soon so that they are protected for the coming fly season. – SM

Dear SM,
This is a tough one, as the evidence to support the use of garlic and other products (apple cider vinegar, diatomaceous earth) to repel insects is mostly anecdotal. That is, numerous owners report excellent results from giving their horses garlic to deter biting bugs. In fact, many people swear by these natural products and continue to use them year after year.

Due to the widespread popularity of garlic in horses, several research studies have evaluated the safety of this herb since very high amounts are known to cause a specific kind of red blood cell disorder. A paper published in 2005 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 1100 pound horse would have to eat 4.4 ounces of pure garlic in two separate meals. That’s 125 grams or 125,000 milligrams. Now, this is much more garlic than any equine supplement contains or recommends be given. For example, there is 1,500 milligrams of garlic in one serving of SmartBug-Off Pellets, or about 83 times lower than the upper safe limit as determined by this particular study.

Try giving garlic to your horse and see if you notice a difference in the number of flies, mosquitos and even ticks that think your horse is a tasty morsel. If you do, then I wouldn’t hesitate to keep him on a daily garlic-containing supplement for the duration of the season. If you do not notice a difference, then unfortunately garlic doesn’t react with your horse’s individual chemistry to discourage these pests. And because supplements that contain garlic work on an individual, horse-by-horse basis, if your horse is the only one in the barn that receives garlic, lucky for you!

Lydia F. Gray, DVM, MA SmartPak Staff Veterinarian and Medical Director Dr. Lydia Gray has earned a Bachelor of Science in agriculture, a Doctor of Veterinary Medicine (DVM), and a Master of Arts focusing on interpersonal and organizational communication. After “retiring” from private practice, she put her experience and education to work as the American Association of Equine Practitioner’s first-ever Director of Owner Education. Dr. Gray continues to provide health and nutrition information to horse owners through her position at SmartPak, through publication in more than a dozen general and trade publications, and through presentations around the country. She is the very proud owner of a Trakehner named Newman that she actively competes with in dressage and combined driving. In addition to memberships in the USDF and USEF, Dr. Gray is also a member of the Illinois Dressage and Combined Training Association (IDCTA). She is a USDF “L” Program Graduate and is currently working on her Bronze Medal. Find Dr. Gray on Google+

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8 comments on “Do fly control supplements really work?
  1. Katherine Heckler says:

    I use the pre-measured smartpak dried garlic on two of my horses, One is about 1050lbs and the other is a pony about 550lbs. I love this stuff. So far it seems to be working. do I need to worry about this blood disorder? They only get this once a day in the mornings with their feed. I was hoping to find out about putting my yearling on this as well if she is old enough. Please reply as I am concerned now about this blood disorder mentioned.
    Kathy Heckler
    PS>…. could you advise about putting my yearling on this?

    • SmartPak SmartPak says:

      Hi Katherine, thank you for your question. The key thing to understand about garlic and Heinz Body Anemia in horses is the volume of garlic the horse would have to consume to get to the point where this condition develops. Horses in the study consumed 4.4 ounces of garlic twice a day, for a total of 8.8 ounces daily (125,000 mg). That is a lot of garlic! The amount of garlic you’re going to find in equine insect control supplements is going to be substantially smaller. For example, SmartBug-Off Pellet contains 1,500 mg of garlic per serving, which is 83 times less than the upper safe limit as determined by this study. If your horses have been doing well on the garlic supplement you’ve been using, I wouldn’t hesitate to continue using it throughout your bug season! ~Dr. Lydia Gray

  2. Nellie says:

    rather than paying for a fly control supplement i’d rather try just adding a bit of garlic to my horses morning feed to see if that works for her first before spending money on a supplement.

    Am I able to just add garlic from the grocery store to her feed?
    if so, how much is safe for a horse 1,000-1,200lbs and what form of garlic?

    • SmartPak SmartPak says:

      Hi Nellie, thanks for your question! If you’re going to try supplementing your horse with garlic, we would recommend sticking to products that have been developed specifically for horses by knowledgeable manufacturers. One of our favorite options for simply garlic, is Garlic Flakes (, which is manufactured by the highly reputable Hilton Herbs. – Dr. Lydia Gray

  3. Hanna says:

    I just came across this site wile looking for a good large animal vet blog and I was wondering if the garlic could also work on bovine. We have two, one year old calls we are raising for meat and in the simmer they would be a walking blood sucking bug attractors and we have tried every thing from dust, to sultutions, and bugs to eat the flys and natural repellents. We wear also wondering if it would flavour our meat?

    • SmartPak SmartPak says:

      Hi Hanna, this product was formulated specifically for horses. If you’re looking for a supplement for your cattle, we would recommend speaking with your large animal veterinarian to determine an appropriate product for cattle. – Dr. Lydia Gray

  4. Dana says:

    I am looking into the Smart Bug-Off supplement for my horse this year. The flies and gnats at our barn are horrible. I can’t stand to go out there during daylight hours in the summer. My problem is that I have one horse in a barn with 19 others. If my horse is the only one on this supplement, will it still work? Or does every horse have to be on it for it to be effective?

    • SmartPak SmartPak says:

      Hi Dana, thanks for asking!
      The good news is that yes, even if your horse is the only one in the barn receiving a targeted supplement like SmartBug-Off, it can absolutely still provide support. Supplements like SmartBug-Off provide ingredients like garlic and apple cider vinegar to help deter biting flies from that individual horse, while also supporting skin and coat health and a healthy response to inflammation with ingredients like omega 3’s and MSM. The beauty of these types of products, is they can provide support to a single horse regardless of what the other horses in the barn receive. – Dr. Lydia Gray

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