Equine Allergies:Dealing with Allergies That Can Affect Your Horse’s Performance

By Cynthia McFarland

Horses in a field

Something’s not right.

You know your horse, and when something’s “off,” you pick up on it in a hurry.

You plan on entering an event at the end of the month and he needs to be at peak performance because the competition is going to be tough.

For the past week or two, it seems as though his breathing has been more labored than usual when he’s working hard. He’s fit and in good condition. He’s up-to-date on all vaccinations. You’ve taken his temperature and he’s not running a fever. You’ve considered every angle and nothing has changed in your feeding or care routine. You did get in a new shipment of hay last month; it’s the same type of hay you always feed, but it did come from a different supplier.

Hmmm … you may have found the culprit, and allergies could be to blame.

“Allergies can develop at any time in a horse. Far and away, airway allergies are the most serious when it comes to limiting performance,” notes Martha Mallicote, DVM, DACVIM, Clinical Assistant Professor at the University of Florida Large Animal Hospital in Gainesville, Florida.

“Most often, these allergies are related to hay or plants found in pasture,” she adds. “Interestingly, it is not necessarily the hay itself that causes some problems, but rather the molds and dusts found in hay. Even hay that is not overtly moldy will contain some molds, and all hays are dusty. These substances can be extremely reactive and elicit an allergic-type response in the lower airway of the horse. These allergies can manifest themselves initially as poor performance during the horse's normal work, but may ultimately lead to clinical signs even at rest or with only very light work.”

Allergic Reactions

In horses, most allergies affect the skin and or the respiratory system. In either case, an allergy is a hypersensitivity to an allergen, which stimulates the immune system.

Skin allergies can typically manifest as hives, itching, rubbing, scratching, hair loss and areas of thickened skin.

“The vast majority of allergies in horses do not result in anaphylactic-type reactions that we can see in people with certain food allergies, like peanuts,” says Dr. Mallicote. “We commonly see hives, often within a day after exposure to the specific allergen, such as new bedding, new hay, pasture change, etc.” A horse may develop a temporary case of “contact dermatitis” after coming into direct contact with a specific weed or type of vegetation. In this situation, the irritation is usually short-lived and resolves itself after a few days. Thorough washing of the area and topical treatment to relieve skin irritation may speed up the process of resolution.

Hypersensitivity to insect bites can wreak havoc with a horse’s skin, causing a horse to itch so intensely that he will walk away from feed to rub the affected skin area(s).

Respiratory allergies usually result in labored breathing, coughing, reduced performance and intolerance to exercise.

“For respiratory allergens, horses may have an unexplained decrease in performance to start with and it will progress to include coughing or nasal discharge when working, or an increase in respiratory effort when working,” notes Dr. Mallicote. “Eventually, these reactions can be severe enough that they are abnormal at rest, with increased respiratory rates or effort when not doing any type of work.”

Airway inflammation is the source of most respiratory allergic problems. “In terms of medical treatments, we often rely on steroids — either given systemically or via inhalers — using one of the systems designed to adapt inhaled medications for equine use,” explains Dr. Mallicote. “But it is perhaps even more important to institute management changes to ensure successful treatment in these cases. The horse must be managed in such a way as to reduce or eliminate exposure to airway allergens. Steroids are ideally not a lifelong treatment but rather a short-term plan while management changes can take effect.”

Some horse owners have had success treating allergies with acupuncture and Chinese herbal medicine. Results vary by case and may, depending on the specific situation, be combined with Western therapies, including medication.

Pay Attention to Environment

The horse’s daily environment can increase or decrease his exposure to possible allergens.

For example, once you know a horse is at risk for developing insect bite hypersensitivity, careful management may prevent future flare-ups. Such horses will require multipronged treatment, which may include corticosteroids, routine application of fly repellent products and/or use of fly sheets, masks, boots, etc., and strict management practices to reduce exposure to insects, such as stabling during hours of peak insect activity and use of fans in the stall.

When it comes to respiratory allergies, performance horses are often stabled a majority of the time. This can increase their exposure to dust and other particles that can aggravate airway inflammation. Feeding practices can also increase the odds of respiratory allergies. The use of round bales is discouraged as these tend to be dusty and can be a serious source of allergens.

Dr. Mallicote recommends soaking hay prior to feeding, as this has been shown to greatly reduce dust. “The hay should be soaked at least thirty minutes and up to two hours prior to feeding. Some people have found the commercial hay steamers to be useful in accomplishing this effort,” she notes.

“Stalls should be bedded in the least dusty way possible,” adds Mallicote. “There are also various commercial products that are available with minimal dust content. Paper or cardboard shavings are available and may help. If stalls are bedded in wood shavings, the shavings should be wetted down prior to the horse going into the stall. Horses should be removed from the barn when you’re cleaning the stalls and when sweeping or blowing out barn aisles. Keep windows and doors open to allow good ventilation and make sure stalls are cleaned well to prevent ammonia odors.”

As with any health concern, the sooner you catch the problem and begin treating it, the better. Unfortunately, equine allergies tend to recur once a horse has begun having issues. In some cases, careful attention to management practices and controlling the horse’s environment can limit or eliminate future flare-ups, but ongoing vigilance is necessary because the potential for allergic issues remains. “Allergies often do end up being permanent,” says Dr. Mallicote. “Since so many allergies are due to various plants [grasses and weeds] in the horse’s pasture environment, their exposure can drastically change year to year, or if they move to a new part of the country, or sometimes even just to a new property. Allergies certainly do end up being a management challenge, first and foremost, and do require lifelong attention.”

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