Managing Bug Bites in Horses

Learn how to properly repel insects and manage itchy bug bites in your horse.
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Culicoides
Midges or Culicoides can cause itchy bites on horses, especially at night, when they’re most active. | Courtesy Scott Bauer/USDA/Bugwood.org

Q. My horse is turned out at night, so I don’t often see what he’s doing in the paddock. He comes in some days with one or two big welts on his body, which look like they’re from bug bites, and they make him very itchy. My horse does not tolerate fly gear such as fly sheets very well. What can I do to prevent these? Is there anything I can do to relieve the itching when they do happen?

A. Many blood-sucking insects, such as midges and mosquitoes, are most active at night, which is when many horses are turned out during the hot summer months. It sounds like your horse gets those bites while turned out at night. 

To prevent these reactions, make sure you heavily spray him with insect repellent before turnout. The most effective options to repel insects are either chemical (i.e., at least 1% permethrin or 0.15% cypermethrin) or botanical (at least 1% neem oil). The chemical products typically last longer but, whatever you choose, be sure to heavily spray the horse (or wipe on the repellent)—don’t just apply a light mist. 

If in the morning you see evidence of bites and swollen lesions, you can use topical steroids such as hydrocortisone, which you can buy over the counter. For some allergic horses that are itchy on a consistent basis, I find it can be helpful to add dexamethasone to the horse’s fly spray. You can ask your veterinarian if that is appropriate for your horse. I typically add 6 milliliters of dexamethasone to one bottle of fly spray so that when I spray the horse, I also deliver some relief for the itching. Depending on your veterinarian’s advice, you might be able to use this routinely during the worst weeks of the summer.

Antihistamines such as dyphenhydramine and cetirizine have been shown to be somewhat ineffective for itching in horses, but they help with hives. So, if your horse develops actual hives, antihistamines might be helpful, but it’s important to note that not all horses with hives are itchy. If the lesions you see on your horse are soft and disappear when you press on them, they are hives.

Ultimately, the best way to help your horse is to prevent insect bites with diligent use of fly repellents at the time when insects are most active, which is from sunset to sunrise.

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Dr. Marsella is a veterinary dermatologist and a full Professor at the University of Florida, College of Veterinary Medicine. Dr. Marsella has a special interest in equine dermatology. She has led the International Committee which has published the Clinical Consensus Guidelines on Equine Allergic Skin Diseases published in 2023. She has also authored a book on equine dermatology which is geared toward equine clinicians that have a special interest in dermatology. She has devoted the last few years working on mechanisms of pruritus in horses and has worked on the identification of alternative treatments to provide relief to itchy horses. She has also tested topical bacteriophages for the treatment of equine pyoderma in the attempt to identify antibiotic free alternative treatments for equine infections. She has published on the trends of antibiotic resistance at her referral institution, the University of Florida. Dr. Marsella is an avid equestrian, rider and owner.

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