Sweet itch is a common term used to describe an allergic reaction to insect bites in horses. It is also called Seasonal Equine Dermatitis or Equine Insect Bite Hypersensitivity. Of all the equine allergies, sweet itch is the most common suffered by horses worldwide. It is also one of the most frustrating for horse owners to manage. However, there are steps that owners can take to help mitigate exposure to the insects that cause sweet itch, while also helping alleviate any symptoms in their affected horses.

What Exactly is Sweet Itch?

Sweet itch differs from seasonal allergies and food allergies. This is because sweet itch is a specific allergic reaction to the proteins in the saliva of biting midges, gnats, or mosquitoes. It is important to remember not all horses will develop an allergy to insect bites. Yet, it is more common than we would like. Furthermore, while all horse breeds are affected, some argue warmbloods are at an increased risk.

With sweet itch, horses usually will not experience an allergic reaction with just a single insect bite. However, just a few bites can trigger a reaction. The most common time of year when horses suffer the most is during the late spring and summer when insect populations are at their highest.

Horses in areas like Florida in the Southern United States with heavy insect populations tend to suffer more and for a longer duration compared to more temperate parts of the country.

Some signs of a horse experiencing a sweet itch allergy include:

·        Above normal irritability with insects
·        General itchiness with excessive scratching and rolling
·        Horse bites or chews irritated areas on its skin  
·        Heavy and consistent tail switching
·        Hair loss due to itching
·        Exposed skin may become lumpy, or skin is inflamed with crusty sores
·        Weight loss due to stress

While the horse can be itchy all over its body due to sweet itch, the most common areas affected include:

·        Mane along the neck
·        Tail head (dock of tail)
·        Legs
·        Face
·        Ears
·        Ventral midline (belly)

How Can We Manage Horses Affected by Sweet Itch?

Afflicted horses usually develop sweet itch early in in their lives. Then as they age their allergy will worsen. Thus, it can be frustrating for owners to watch their horses suffer. However, a focused management plan can alleviate a horse’s symptoms from sweet itch and bring some much-needed relief.  

First, when your horse suffers from any allergy it is always recommended to discuss this with your veterinarian. Your veterinarian can do diagnostic tests like injecting midge extracts under the skin to monitor for a reaction. However, it is worth noting allergy testing is not always accurate. Regardless, consultation with your veterinarian is a crucial step in management and treatment. If the allergy is severe enough, they may prescribe topical ointments or systemic medication to help your horse.

Second, with regards to sweet itch, prevention is the best course of action. The first line of defense against biting insects are fly repellents. However, not all fly repellent sprays are effective. You can discuss the best repellents with your veterinarian. Those products containing permethrin or pyrethroid are the most effective against biting midges, and daily use can help reduce exposure.

Another option to help prevent sweet itch is the use of fly masks, ear masks, or full body fly sheets. Yet, these preventive items need to be put on the horse before they are experiencing allergic symptoms. If placed on the horse suffering from an allergy, the horse will continue to scratch potentially damaging the fly sheets or masks. Additionally, these may not be the best option in hot and humid environments as it will make the horse even more uncomfortable with a buildup of heat or create a moist environment for bacteria.

Other tips to limit exposure to biting insects include:

·         Limit horse turn out time in early morning and late afternoon/evening as insect activity is at its highest
·         Manure management is important in keeping biting fly populations down
·         Stable horses indoors with fans at night
·         Stables with ultrafine screens can keep midges out
·         Avoid turning horses out in areas near ponds or other standing or stagnant water
·         Clean water troughs often to reduce larvae populations of biting insects

Finally, practicing good fly control in barns will help alleviate exposure to your horse to biting insects. It may also be beneficial to feed your horse a feed supplemented with fly control to help reduce insect populations.

Can Nutrient Supplements Help Alleviate Symptoms of Sweet Itch?

For horses with dry or damaged skin, or those suffering from sweet itch, diets high in omega-3 fatty acids (FA) have shown to be beneficial in reducing the allergies severity. A research study out of the University of Guelph in Canada demonstrated that horses supplemented with flaxseed (high in omega-3 FA) suffered less with sweet itch compared to horses not supplemented. Other studies have also shown the benefits of feeding omega-3 (FA) in reducing allergic symptoms of sweet itch. Scientists surmise that omega-3 FA and their anti-inflammatory properties help diminish skin irritation due to sweet itch.

Many high-end quality feeds are already bolstered with the proper ratio and amount of omega fatty acids and other nutrients that help horses maintain healthy skin and coats. You can learn more about the benefits of feeding omega fatty acids and other healthy skin nutrients HERE and HERE.  

Take Home Message
It is frustrating for any horse owner to watch their animals suffer from sweet itch. However, with discussions with your veterinarian and a careful management plan, a horse’s condition can and does improve. Furthermore, ensuring your horse is eating a diet high in omega-3 FA and the other nutrients that support healthy skin do help alleviate suffering. If you have any questions or concerns on what you are feeding your horse, please feel free to contact us.

Resources

O’Neill, W., McKee S., Clarke, A.F. 2002. Flaxseed supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity. Can. J. Vet. Res. 66:272-277.
Huhmann, R., Mueller, R.S. 2019. A cream containing omega-3-fatty acids, humectants and emollients as an aid in the treatment of equine Culicoides hypersensitivity. Vet. Derm. 30:155-e46.
 

CHRIS J. MORTENSEN, PH.D.