Horse allergies: symptoms, treatment and prevention

Don’t let horse allergies get in the way of your riding plans this spring.

We have all been there. It’s a sunny spring day, perfect for a walk. As you make your way to the barn to get into the saddle, you hear coughing. As you turn the corner, you see that the culprit of the cough is your horse.

Flared nostrils, even when at rest, are a sign of airway allergies like equine asthma. Photo by Marie Charouzova/shutterstock

In another barn, a rider grabs the grooming kit to brush her horse in preparation for the saddle. As she runs her hand over her neck, she feels, then sees, numerous bumps, some of which have merged into large bumps.

What’s going on with these horses? Allergies.

A world teeming with horse allergies

Invisible to the naked eye, the world is full of proteins and substances that can cause an allergic reaction. These allergens can be inhaled, ingested or can affect a horse through topical contact. You will be alerted to signs of trouble when you notice your horse has itching, hives or breathing problems.

Allergies are common in the human and animal world, and horses are no exception. Usually, horses do just fine in their environment without developing any obvious signs that microscopic compounds are affecting them. Horse allergies occur when a horse’s immune system overreacts to a foreign protein, goes on the offensive, and becomes hypersensitive.

Sometimes it takes months or years of accumulated exposure for a horse to become hypersensitive; sometimes the response is more immediate and acute. Whichever specific protein causes the reaction, it triggers a cascade of inflammatory events that release prostaglandins and histamines to create obvious allergic skin or respiratory signs.

Skin allergies in horses

Horse allergies that manifest in the skin can result from topical contact, but can also develop from oral ingestion or inhaled particles. Aerosol dust, mold, pollen, bedding, and insect bites are just a few of the sources that can cause itching and/or hives.

A major cause of itching begins with the bite of insects called Culicoides, also known as gnats or no-see-ums. While midges tend to feed on the abdomen, a horse exhibits an allergic reaction to midge saliva aggressively rubbing its tail, hindquarters, neck and mane due to intense itching. These areas become raw, crusty and inflamed, with severe hair loss.

Certain breeds and lines of horses tend to be particularly allergic to gnats, such as Morgans, Icelanders, and Arabians. The solution is to keep the horse away from areas that are good for midge breeding, such as ponds, wetlands, and slow-moving streams.

fly sheet to prevent insect bites
Mosquito nets with belly panels provide protection against biting midges, as does guarding horses at dawn and dusk when these pests are most active. Photo by Ro_Ma_Li/shutterstock

Fly sheets are important, but they should have mesh belly bands. Bringing a horse indoors at dusk and dawn also helps reduce exposure to midges, as this is their preferred feeding time.

Unlike an itch reaction (pruritus), hives are usually not itchy, but a sure sign of exposure to some kind of allergen. Hives tend to be soft swellings that deepen when you push with your finger, called piquant oedema.

They can vary in size, sometimes merging into a single large stripe when several are close together. Inhaled allergens can also cause hives, called atopic dermatitis.
Contact dermatitis is also not unusual. An example that occurs quite frequently is hives caused by contact with pine litter. If there is a suspicion that bedding is a problem, replace paper bedding or another source of pine bedding to see if the hives go away.

Some shampoos or fly sprays can cause skin irritation and hives, as can laundry detergent residue or dirt on a saddle pad. On rare occasions, a horse with a fungal infection called ringworm may develop hive-like reactions around a fungal lesion.

Hives are bumps on the skin, signaling exposure to some form of allergen. Often this happens through direct contact with the culprit, such as bedding or a particular shampoo. Photo by Horse Crazy/shutterstock

Hives can develop acutely and disappear just as quickly. Sometimes they persist long after the allergen has been removed from the environment. In difficult cases, it may be necessary to treat the horse with a short course of a corticosteroid such as dexamethasone or prednisolone, which are effective anti-inflammatory drugs.

Certain foods can trigger a skin reaction, although food allergies are not that common. If it is a food allergy, however, it is often difficult to determine the exact food or oral substance that is the culprit.

This may need to be done through a process of elimination: eliminate all foods and supplements and start by giving only grass hay, although diet changes may need to be made slowly. Check with your veterinarian. After a few weeks without signs of hives lesions, add another food item and wait a week or two before adding another. This can help identify the cause.

Supplements tend to be the most likely culprit, far more so than hay or animal feed, although alfalfa has been known to cause allergic reactions.

Respiratory Allergies in Horses

Respiratory allergies can affect horse performance by affecting breathing and comfort, especially during exercise. A horse with a respiratory allergy often has a dry cough or wheeze that gets worse when eating or exercising. There may also be a chronic or intermittent runny nose.

airborne allergens for horses
Airborne arena foot is a common respiratory irritant that can cause a persistent cough. Photo by Montreal Firefighter/shutterstock

Respiratory health is at risk when horses are kept indoors, especially those with poor ventilation, and/or exercised in indoor riding arenas. Many toxic compounds are aerosolized to circulate in the air of these environments: endotoxin (part of the cell wall of Gram-negative bacteria) in manure, ammonia vapor from urine-soaked bedding, mold spores from hay or filter hay dust when stored. in the lofts above the stalls or the arena. Arena foot can also contribute to respiratory irritation.

The best solution is to minimize the time a horse spends indoors and take them outside as much as possible. Better yet, organize a full-time outdoor life with break-in sheds to protect you from the elements. Soaking or steaming hay before feeding helps settle dust and mold.

If barn living is all you have, proper ventilation is very important. Use appropriately placed fans, open windows, and open barn doors to keep cool air circulating. Store hay in a separate building from horse housing.

horse allergy
Hay mold spores and ammonia fumes from soiled stall bedding are two culprits of respiratory irritation. Open doors and windows and use fans to increase the circulation of fresh air in the barns as much as possible. Photo by Heureeka/Shutterstock

Another important respiratory health strategy is to keep your horse on a regular vaccination schedule, especially against respiratory viruses. Equine influenza virus is known to cause long-term respiratory damage, including the development of equine asthma. Discuss an appropriate vaccination schedule with your veterinarian.

Once a horse develops equine asthma, a variety of medications, including inhaled and/or oral bronchodilators, can help improve its comfort and ease of breathing. It’s much easier and more effective to apply an ounce of preventative respiratory health strategies than a pound of remedy to deal with after the fact.

Equine Anaphylaxis

In a case where a horse’s immune system develops a deep and severe reaction, a horse can experience life-threatening anaphylaxis. With this in mind, it is important to contact your veterinarian immediately when you notice signs of an allergic reaction, particularly if your horse has difficulty breathing and/or has swelling of the face and muzzle or limbs and leg. stomach.

If your horse has a known allergy to any medication, such as penicillin or a non-steroidal anti-inflammatory drug (NSAID) such as phenylbutazone or flunixin meglumine, it is essential to post warning signs on the door and paddock of the horse to avoid the accidental administration of potentially fatal drugs.

horse allergy treatment
In severe cases, horses with equine asthma may need nebulizer treatments with corticosteroids to reduce inflammation. Photo by Nancy S. Loving, DMV

People with allergies wear neck tags or wristbands to convey this essential information, but for horses it is necessary to post signs in obvious places. Notify your stable manager and staff, friends and veterinarians who may be caring for your horse.

Allergies can be difficult to resolve, so observe and monitor all facets of your horse’s environment. With knowledge of potential problems, you can prevent allergic problems before they start.

This article on horse allergies originally appeared in the May 2021 issue of illustrated horse magazine. Click here to subscribe !

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