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

For More:

• For more tips on how to protect your horse from pesky and disease-carrying insects this summer and for our shopping guide on protective fly gear—including fly sheets designed specifically for sweet-itch protection—click here.
• Learn how to avoid the top-three summer equine health issues here.

Besides being annoying, biting insects can carry infectious diseases, trigger allergies and cause excessive stomping which can lead to injury or poor hoof quality, so minimizing bugs is key.

While fly spray can help, its duration is limited and can wear off over time, especially during heavy sweating. In this case, fly sheets, masks and boots are your next line of defense against biting insects. These fly barriers also have the bonus of protecting your horse from harmful UV rays, which can cause a sun-bleached coat or sunburn on pink- or sensitive-skinned horses. 

Fly Sheets 

There are a variety of fly sheets on the market, and finding one that’s lightweight and breathable but also durable is key to keeping your horse cool and protected during the summer heat. 

Look for a fly sheet that’s lined at the shoulders and tail for durability, and make sure it has shoulder gussets to provide maximum range of movement to prevent shoulder rubs. Many fly sheets, such as those from Weatherbeeta, are made with 210T lining, which is a ripstop fabric with quality structure that also dries quickly.

Depending on your horse’s needs and tolerance to heat, some fly sheets have a built-in neck cover or detachable neck cover to help protect the neck area from biting insects. A wide belly wrap is key to protecting the sensitive underbelly where gnats (also called no-see-ums) love to bite, while fleece at the withers can help minimize rubbing. Fly sheets offer up to 95% UV protection depending on the material, so pay attention to that factor if sun protection is one of your concerns. 

Fly sheets are available in various meshes. The type of mesh you choose will depend on your horse’s tolerance to heat as well as how rough he tends to be on his clothing, but keep in mind that the thinner the mesh, the less UV protection it will provide. Research has shown that patterns create an optical illusion to flies which deters them from landing. A wild-patterned fly sheet may not be everyone’s taste, but it could provide a little more armor in protecting your horse from flies.

While most fly sheets dry quickly, if rain rot or other skin fungus is an issue for your horse, consider a sheet with a waterproof lining over the topline like the WeatherBeeta ComFiTec Dual Shield with a detachable neck cover. Its 600 denier ripstop waterproof upper panel helps keep rain off your horse’s back and it has a lower open-weave mesh for increased airflow to keep him cool in warmer weather. If your horse is prone to sweet itch—an allergic reaction to the bites of Culicoides midges—consider a special sweet-itch sheet like the Weatherbeeta ComFiTec Sweet Itch Shield Combo Neck.  

Fly Masks & Boots 

Fly masks can be a lifesaver in the summer for sensitive horses and those prone to melanoma. Made with or without ears covers, the choices can be daunting, but the best choice is the one your horse will keep on! From zippers to single and double hook-and-loop closures to pull-on styles, fly masks are available in many options, so find one that’s best for your horse’s lifestyle.

If your horse has sensitive eyes, fly masks with raised see-through mesh over the eye area provides unobstructed visibility while also protecting his eyes from flies and UV rays. UV protections also range, so be sure to choose the right amount for your horse’s needs. Some fly masks come with an extended or detachable nose cover to protect horses with sensitive pink muzzles. 

If you ride your horse with a fly mask or turn them out in a halter, the Weatherbeeta ComFiTec Hexi Shield Dual Fly Mask has an attachment with an emergency release mechanism. 

If your horse’s legs are also sensitive to biting insects, fly boots or wraps are another option to keep him covered from head to hoof. WeatherBeeta’s ComFiTec Hexi Shield Fly Wraps feature a nylon fabric that reflects sunlight, protects from UV rays and contours around the legs. Again, the type of mesh will depend on what your horse requires. Look for sturdy enclosures to ensure the boots stay on during turnout.  

Summer Turnout Tips 

Once your horse is outfitted in appropriate fly gear, there are additional ways to manage his comfort during the summer heat. 

• Fly management for your horse and in the barn is key. Fly sprays and other topicals can deter flies using a vapor barrier or natural or synthetic insecticides. If your horse regularly works up a sweat or you bathe him often, you’ll have to reapply any topical.  
• Feed-through supplements have shown promise in lowering the fly population around a barn. Some contain ingredients that safely pass through the horse’s system into their manure to prevent fly larvae and pupa from developing, while others include apple cider vinegar or garlic to make horses less unappealing to flies. 
• Sprinkling Fly Predators® around manure piles and near barns can help keep certain types of flies at bay. These wasps kill developing flies before they hatch without harming horses or people. 

• Turn your horse out at dusk or overnight (if possible) when the temperatures are cooler and the sun isn’t as strong, but keep an eye out for evening thunderstorms. 
• Provide access to shady areas and/or offer shelter with a run-in shed for relief from the sun. 
• Make sure your horse has access to clean, cool water and check the trough often for algae and dirt. 
• If your horse has Cushing’s disease or tends to maintain a longer coat throughout the summer, consider clipping to keep him cool and prevent overheating. 
• If your horse is showing signs of heat stress, such as rapid breathing, lethargy or a high temperature, move him to shade immediately and cool him down with water and a fan. 
• If your horse suffers from anhidrosis (a condition that causes some horse to sweat less or stop sweating altogether in hot and humid weather), check with your vet to determine if he might benefit from supplements, other nutrition-based approaches or alternative remedies, that can help control anhidrosis symptoms. (Click here for more advice on how to manage anhidrosis in horses.)
• On the other hand, if your horse sweats heavily throughout the summer, you might consider giving him electrolytes to help replenish vitamins or minerals lost through sweat. Electrolyte supplementation can also encourage your horse to drink more water, which will help rebalance his fluids and ensure proper digestion.

For more tips on creating an effective fly-control program for your horse and barn, click here.