You want your horse to enjoy being turned out this summer, but if he’s prone to sweet itch—an allergic reaction to the saliva of biting insects, most often the Culicoides species of midges and gnats—pasture time can be miserable for him. Also called no-see-ums, these tiny insects love to feast on equine flesh and their bites cause intense itchiness that can drive horses to rub away patches of hair, leaving the skin underneath raw and weepy. If a case is severe enough, your horse may even lose weight if he spends more time scratching than eating.
Here, we look at what causes sweet itch, how to spot the signs that your horse might be gnat food and offer tips on how you can protect him from these miniscule, mighty-mouthed foes. Plus, we look at a study that confirmed horses can inherit a susceptibility to sweet itch.
Sweet Itch: At A Glance
Definition: Technically known as equine insect hypersensitivity (EIH), sweet itch is an allergic reaction to the saliva of biting insects, most often the Culicoides species of midges and gnats.
Signs: Intense itchiness, wheals and swelling, primarily on the neck (under the mane), face, shoulders, withers, belly and rump (over the tail). The skin may be rubbed until it is crusty, weepy, raw and hairless. Location of the lesions may depend on the specific species of gnat; most prefer to bite on the neck and along the topline, but some target the chest, belly, tail and groin.
Diagnosis: Skin scrapings and cultures may be needed to distinguish EIH from other causes of itchy dermatitis, such as mites, lice and fungal infections.
Treatment: Antihistamines or corticosteroids may help ease the itch and inflammation, providing relief to the itchy horse; antibiotics or antimicrobial shampoos can help prevent secondary infections. Pentoxifylline can be used to decrease skin reactivity, and in some cases allergy serum is worth trying.
Of Note: The condition is usually at its worst during the spring and summer when insects are most active, and it may subside during the winter. Less than 10 percent of horses in the United States develop sweet itch. Most horses won’t begin to show signs until they are 2 to 4 years old, and the condition is more common among Shires, Welsh Ponies and horses imported from Iceland, but it can occur in any breed.
Protect Your Horse
Research is underway to develop a reliable immunotherapy treatment for sweet itch. In the meantime, veterinarians may prescribe antihistamines and corticosteroids to help relieve the signs of the condition. But steroids carry a low but real risk of serious side effects, including laminitis. So, if your horse is susceptible to sweet itch, you’ll want to reduce his exposure to the insects that cause it. Here are steps you can take:
1. Stable your horse during peak biting hours. Culicoides spp. are most active at dusk and dawn, so bring your horse into a stall during those hours. For additional protection, install ultrafine screens in stall windows and set up fans to provide a continuous breeze over stabled horses. Gnats are weak flyers and even a slight breeze will keep them away. You might also consider applying a spray repellent designed for use on stall walls and other surfaces inside the barn.
2. Keep your horse covered. One way to reduce bites is to keep a fly sheet on your horse during insect season. Made of fine mesh and equipped with closures to keep out bugs, clothing designed specifically for horses with sweet itch has extensions to cover the neck, belly and tail, the areas where Culicoides spp. are most likely to bite. A fine-mesh mask may also be needed to protect the horse’s face and ears.
3. Use fly-control products. The most potent products combine repellents with pesticides. Look for ones labeled for use against gnats and midges. You’ll need to be diligent about applying the sprays and wipes as often as the manufacturers’ instructions allow.
4. Restrict your herd’s access to marshy areas. Gnats breed in marshy, shady ground with rotting vegetation. If possible, move your horse to a pasture in a drier, more exposed location away from boggy terrain. Around your barn, clear up standing water in ditches and gutters and keep them free of leaves and other debris. Place manure and compost piles as far away from the horses as is feasible.
5. Try over-the-counter products. You’ll find a number of products for horses with sweet itch, from feed supplements formulated to reduce inflammation, to topical preparations meant to soothe itchy, inflamed skin. Thick, oily or sticky ointments are messier but may keep gnats from landing on the horse’s skin. They may also help keep bugs from getting to the skin to bite. Anecdotal evidence suggests that these products offer some relief, at least in some horses. When trying a new topical product, start by applying it to a small area to make sure it will not further irritate sensitive skin. Be careful with tea tree oil, lavender and other herbals—they are soothing to some horses but can irritate the skin in others.
More Tips & Tricks
Here are a few home remedies recommended by riders to help prevent or reduce your horse’s exposure to the gnats that cause sweet itch:
- Apply Avon’s Skin So Soft bath oil to the most vulnerable areas.
- Add apple cider vinegar and/or garlic powder to your horse’s feed to make his sweat’s smell less attractive to gnats. (There are also supplements available that contain both apple cider vinegar and garlic.)
- Apply menthol products like Vick’s VapoRub to susceptible parts of your horse’s body.
- Rub a scented dryer sheet over his body.
- Apply baby oil to the roots of your horse’s mane and tail head; gnats can’t seem to get a grip on the skin to feed.
Genetic Connection for Sweet Itch?
A long-term study from the Czech Republic confirms that horses can inherit a susceptibility to the allergic skin condition known as “sweet itch,” which is technically known as insect bite hypersensitivity (IBH). The study focused on Old Grey Kladruber horses, a native warmblood breed, at the National Stud in Kladruby and 10 private breeding facilities.
The same person visually inspected the horses over a period of 13 years, from 1996 to 2009, scoring the severity of any signs of IBH at each observation. A total of 1,209 observations were entered in a database, along with information about each horse, including location, age and pedigree.
In statistics, the degree of a trait’s heritability is expressed on a 0 to 1 scale, with 0 meaning that none of the variability of the trait among individuals is the result of genetics and 1 meaning that genes are responsible for all the variability. The Czech researchers found the heritability of sweet itch susceptibility among the study horses ranged from 0.305 to 0.626, depending on the factors considered in the calculations. These numbers, the researchers say, indicate the heritability of sweet itch is “medium to high, so there is a possibility to reduce the prevalence of IBH by selection.”
Reference: “Genetic parameters of insect bite hypersensitivity in the Old Grey Kladruber horse,” Journal of Animal Science, January 2017
