The Adversities of Allergies

Equine allergies affect many horses. Here's what to look out for and how to treat, and avoid, many of the symptoms.

Most people have dealt with it: sneezing, itching, and even shortness of breath. For humans, allergies very rarely go untreated. But for horses, they can sometimes be hard to identify, and can become severe in a matter of minutes. Stable Management spoke with Dr. Jennifer Feiner of Hagyard Equine Medical Institute in Lexington, Ky., and Dr. Langdon Fielding of Loomis Bain Equine Medical Center in Loomis, Calif., to learn about the most common allergies that afflict horses and the preventive measures that can be taken to avoid them.


One of the most common allergens that horses react to are very similar to what humans suffer from: inhaled allergens. Pollen from plants, dust and mold from hay are very common.

The easiest way to tell if the horse is having an allergic reaction is through outward symptoms. “Runny eyes are usually associated with dust or pollen and other allergens in the air,” says Dr. Fielding. Other common symptoms include respiratory problems or swollen eyes. Measures you can take are:

• To prevent reactions to inhaled allergens like dust in the barn, Dr. Feiner suggests turning the horses out while cleaning or sweeping the barn.

• If a horse seems to be showing signs of allergies towards its bedding, try switching to a different type.

• “If they’re allergic to dust in the hay, the best thing to do is wet their hay,” she says.

• If a horse reacts to an inhaled allergen, an antihistamine such as Hydroxyzine, Triplennamine or Diphenhydramine (both are similar to Benadryl) should be administered.

• If symptoms worsen and the horse’s eyes become swollen, Dr. Fielding suggests hosing the horse off with cold water, which decreases inflammation.


Horses also commonly react to contact allergens such as weeds, shampoo or fly sprays. Contact allergens pose more of a problem to equine professionals, because it is more difficult to predict if a horse will have this type of allergic reaction. Some likely scenarios:

• “If they’re allergic to weeds, their legs might swell up,” says Feiner. “A common clinical sign is swelling of the lower limb. It’s usually below their hock or their knee, around the cannon area. Sometimes they have ‘scratches’ and the weeds irritate the skin and cause a cellulitis.”

“For horses with a history of allergic reaction to weeds it may be helpful to keep that horse inside during the morning when there is a morning dew,” says Dr. Feiner. She also suggests taking preventive measures and maintaining the horse’s turnout area by keeping weeds short, or keeping the horse in a paddock where the grass isn’t as high and there are fewer weeds. Feiner also suggests administering Banamine to the horse.

If the leg becomes severely swollen, hosing it off with cold water should also prevent further swelling, and a veterinarian should be contacted.

• Horses also sometimes react to contact allergens by breaking out into hives. If the horse breaks out into hives, the best solution is, again, to rinse the area off with cold water. Other options for minimizing hives include using a Derma cloth or an oatmeal bath, which will remove the allergen from the skin.

“Hives tend to be self-limiting,” Feiner explains. “After bathing and medical treatment, without the recurrence of any new hives, it may take a few days for the hives to go down.”

• If the horse has an allergic reaction to shampoo or fly spray, the best option, obviously, is switching to a different product.


In the spring and summer, insect bites are another common allergen. Flies and mosquitoes are the most frequent irritants. The easiest preventive measures are fly spray, fly masks and fly sheets when turning horses out, as well as fly deterrents inside the barn.

Feiner suggests placing fans in the barn during the warmer months to prevent insect bites: “The air turbulence created by fans makes it more difficult for gnats and midges to fly and thereby decreases their numbers.” She also suggests using a good manure management system—regularly cleaning stalls and keeping a manure pile far enough away from the barn and turnout area so that it doesn’t attract more insects. “It’s also important to keep horses indoors during peak hours of the day, such as dusk and dawn,” she adds.

Insect bites also tend to cause hives. Depending on where the horse has been bitten, the area is likely to get swollen. “The fly bite dermatitis [the inflamed area] is often found under their belly on the midline, in front of the sheath or udder,” says Feiner.

In certain regions snakebites can be problematic, but contrary to popular belief, Dr. Fielding describes the usual result as an immune reaction, not an allergy. “We see a lot of snakebites on the West Coast,” she says. “A lot of the signs from snakebites we see are immune responses. If a snake bit a horse, pretty much all horses would break out or have a reaction, such as a local swelling, but only a few have a huge body reaction.”

A severe reaction to snakebite would include swelling over most of the body or difficulty breathing, such as anaphylaxis. If a horse is having difficulty breathing, it is a good idea to administer either Banamine or Bute and immediately contact the veterinarian. Dr. Feiner also suggests keeping a foot-long hose on hand in the case of airway obstruction, stating, “If the allergic reaction is very severe and their airway gets cut off, this is something that might have to be done [but is best done by the vet].”


Horses also sometimes react to medications and vaccinations. Allergic reactions to both medications and vaccinations can be difficult to prevent. Common reactions include breaking out in hives, developing a fever, or suffering from difficulty breathing, possibly leading to anaphylaxis. In these instances, the veterinarian should be contacted immediately.

While waiting for the veterinarian to arrive, hose off a feverish horse with cold water. If the horse is having difficulty breathing, ask your vet whether Banamine or Bute should be administered.


Skin testing is a common option available to help identify allergies beforehand, as well as to keep track of the horse’s clinical treatment. Both methods can help managers become proactive in treating the horses before allergic reactions occur. Blood testing has also been used in the past, although Feiner explains that it isn’t as accurate as skin testing.

It is always important to consult with a veterinarian beforehand to ensure that all treatments are safely executed. By being proactive and properly executing treatment, horses suffering from equine allergies can lead long and healthy lives.






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