Five Tips for Protecting Your Horse From Flies and Mosquitoes

As temperatures rise, vegetation flourishes and daylight hours lengthen, there’s no doubt about it: summer is on its way. Many riders enjoy the extra sunshine and longer days, but with warmer weather also arrives the bane of every horse owner’s existence: flies and mosquitoes.

These insects are known for their painful bites and general annoying behavior, but they are also the bearers of something much more sinister. Without proper control measures, flies and mosquitoes can transmit some of the deadliest diseases to your horse.

Quarter Horse News spoke with Dr. Amber Grimes of Carter Veterinary Services, located in Hardeeville, South Carolina, to get the low-down on fly- and mosquito-transmitted diseases and find out how to prevent these pests in the first place.

A number of diseases and conditions are spread by flies. The most significant in the U.S. include Equine Infectious Anemia (EIA), summer sores, Vesicular stomatitis and sweet itch. Horses that live in pastures bordering creeks and rivers can also be susceptible to Potomac Horse Fever, and those located in the Southwestern U.S. and other dry, arid areas could be exposed to Pigeon fever. For the most part, none of these diseases, except for Potomac Horse Fever, are preventable by vaccines.

“Fly control is so important for these diseases because there is no other method of prevention,” Grimes said. “Preventing the fly from getting to the horse is crucial in preventing diseases that have major consequences and sometimes no treatment.”

The majority of fly diseases are treatable, but failing to treat them can lead to severe outcomes. For instance, Vesicular stomatitis, which is highly contagious and spreads through biting flies, causes ulcers and erosions on the mouth, tongue, coronary band, udder and sheath. Summer sores, or habronemiasis, are caused when flies deposit habronema larvae into open wounds or mucous membranes, producing an inflammatory reaction that leads to non-healing wounds. Even sweet itch, which is an allergic reaction to bites, can cause hair loss, sores, infection and weight loss.

EIA, on the other hand, is not treatable. Once a horse contracts it, it must either be humanely euthanized or spend the rest of its life in isolation at least 200 yards away from any other equine animals. To prevent EIA outbreaks, horses that leave their property for any reason must be accompanied by a current negative coggins test.

To protect your horse from fly-borne illnesses, the best thing you can do is limit the number of flies on your property. It may sound impossible, but there are several different ways you can create a “no fly zone.”

“Fly masks, sheets and boots are very important because they provide a barrier to the flies to help prevent them from getting on the horse,” Grimes said. “The downside is that some horses don’t tolerate them and pull them off or tear them. Sprays like permectrin also help, but I feel like I always hear that they don’t last very long. Some people install misters that spray at certain times of the day to continually keep the horse covered when in a stall.”

Other fly-control methods include picking up manure from stalls and pastures twice a day at minimum; placing fans on stalls that blow flies off horses; hanging up sticky tape and traps; and applying topical products like Vectra 3D, a monthly flea and tick preventative for dogs that can repel ticks and flies on horses. You can also add a feed-through formula to your horse’s grain, which prevents flies from developing in manure, rather than killing adult flies. It must be fed continuously to all horses on the property, plus horses in neighboring pastures; otherwise, you won’t see much difference.

There are only four significant mosquito-transmitted diseases in the United States, but the ones that are present — Eastern equine encephalomyelitis (EEE), Western equine encephalomyelitis (WEE), Venezuelan equine encephalomyelitis (VEE) and West Nile Virus (WNV) — are quite deadly, with inflammation of the brain being the main symptom.

At 90%, EEE and VEE have the highest mortality rates. EEE is spread when mosquitoes feed on infected birds and then bite horses. VEE, despite its name, is found in many places outside of Venezuela, including the Southern U.S. While its hosts tend to be rodents and birds, which spread the disease to horses through mosquito bites, infected horses can pass the disease to other horses via mosquitoes, too.

WEE is similar to EEE in how it is transmitted, but it has a lower mortality rate at 20% to 40%. Birds are also the natural host for WNV, which has a 35% mortality rate, but while most horses recover, many are left with long-term effects like behavioral and walking abnormalities.

These diseases are definitely alarming, but fortunately, there is good news. All four can be prevented by keeping your horse on a consistent vaccine schedule.

“Mosquito control is important, but vaccines are just as, if not more, important,” Grimes said. “In populations where mosquitoes are very prevalent, it is advisable to vaccinate twice a year to prevent disease from occurring. It is much easier to prevent than it is to treat, especially since none of these diseases have treatments.”

Even if your horses are vaccinated, it’s wise to limit mosquito development on your property for your horses’ comfort and your own. Some of your fly-control measures, like fly boots and sheets, sprays, traps and fans, can help with this, but there are other methods you can employ for mosquitoes.

“Eliminate standing and stagnant water to remove their breeding ground, along with vegetation that could be their habitat,” Grimes said. “Clean your water troughs regularly, and if you have stalls that are completely indoors, you can keep your horses in during dawn and dusk when mosquitoes are most active. There are also natural repellants like garlic, apple cider vinegar and essential oils such as citronella and eucalyptus that are said to repel mosquitoes.”

If you live in a region that is particularly prone to flies and mosquitoes, you may have to employ multiple methods to get some semblance of control. A barrier, like fly sheets, boots and masks is the first step, Grimes said, followed by good environmental practices.

“I believe that a combination of these things is of great benefit,” Grimes said. “Keep the property free of manure, use traps to get the adult flies and mosquitos, give feed-throughs to prevent more flies from maturing and spray repellants. Most importantly on the mosquito side is vaccinations. Vaccination is at the top of my list due to its ability to prevent mosquito diseases. Twice a year vaccination in heavy mosquito populated environments is highly recommended.”

Preventing these diseases is often easier than treating them, so if you don’t already have control practices in place, it’s a good idea to start now. You likely won’t eliminate every fly and mosquito on your property, but by taking preventative measures, you can limit the number that come into contact with your horse. That way, you’ll be able to spend more time riding and enjoying the long summer days ahead.