Preventing Sweet Itch in Show Horses

An equine dermatology expert explains how you can manage and prevent insect bite hypersensitivity (IBH) in riding horses during prime competition (and IBH) season.
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Horses allergic to Culicoides saliva in bites can develop itchy skin reactions around their mane and tail, ears, face, belly, and legs.
Horses allergic to Culicoides saliva in bites can develop itchy skin reactions around their mane and tail, ears, face, belly, and legs. | Courtesy University of Florida

Q. During the warmer months my mare’s insect bite hypersensitivity (IBH, also known as sweet itch) flares up, and she often rubs the underside of her belly to the point where she’s raw and very uncomfortable. How can I prevent, manage, and treat sweet itch? I’d like to be able to ride and show her this year, but her IBH often prevents this.

A. As you have experienced, insect bite hypersensitivity can be difficult for horse owners to manage and can have a major impact on horse health. Insects can transmit parasites and many horses with midline ventral dermatitis, like your mare, have a combination of insect allergy and parasitic disease. For example, Culicoides (also known as no-see-ums or gnats) transmit a parasite called Onchocerca. Horses with cutaneous onchocerciasis have crusting on the belly, shoulders, and chest, and sometimes they also have a round bald spot on their forehead and need to be dewormed. I suggest deworming with oral moxidectin, repeating the treatment every three weeks for a few times, if the lesions on the belly are always present.

To prevent IBH in your mare, you first need to minimize insect bites. Use an effective repellent that will prevent insects from landing on your horse, not just an insecticide that kills a fly when sprayed. For the belly, one of the best repellents is concentrated permethrin. There are roll-on products that have high amounts of concentrated permethrin or permethrin derivatives. Pyrethrin, however, is not an effective repellent, so products that only contain that ingredient are not the best option for horses with allergies, such as yours. These concentrated roll-ons are recommended for problem areas like the belly and typically last one week.

The rest of the body needs to be sprayed with products also containing repellent ingredients such as cypermethrin. In my experience, in a hot humid climate with lots of insects, these products need to be reapplied frequently. Severely allergic horses might need it every day, particularly if they are out all the time, sweating, and being rained on. If your horse is sensitive to these chemicals, you can try neem oil products, either as a concentrate or as a spray. This botanical option can also repel insects and might be tolerated better than other products by certain horses.

Some IBH patients also have a secondary bacterial infection, which significantly contributes to their level of discomfort. Use a chlorhexidine shampoo and spray to treat any crusted, scabbed area. You can shampoo your horse once or twice weekly and use the spray daily between baths until the scabs go away. No scrubbing needed. Scrubbing or picking the scabs is often painful for these horses and can lead to scarring. In areas where your mare is itchy you can use oatmeal rinses and topical anesthetic products with pramoxine in it. None of these options require a prescription from your veterinarian.

Take-Home Message

You can make your mare with sweet itch more comfortable, but it will require diligence and consistency. With regular, correct treatment, she will likely be comfortable being ridden during peak IBH months.

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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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