Pollen Allergy in Horses

Respiratory disease arising out of an allergic response can cause the small airways in the lungs to constrict, which produces fluid and thickens the walls of the airways, making it hard for an affected horse to breathe. This condition can be called acute recurrent airway obstruction (RAO) or heaves, and in chronic cases, chronic obstructive pulmonary disease (COPD). Many types of airborne allergens that can trigger these reactions are present in every barn, such as pollen, dust, fungus and mold.

Horses can become allergic to various types of pollen. Affected horses show signs of respiratory disease, such as coughing and mucus, or they can develop skin irritations that are often itchy, such as hives. A pollen allergy often manifests seasonally, as the pollen counts rise in the air, but can be affected by your location and the weather. 

Symptoms of a pollen allergy are seen seasonally, and can vary based on the amount of pollen inhaled by your horse. If the pollen allergy is concurrent with other allergies, the symptoms may worsen seasonally. Signs for some horses can appear mild for years and progress over time, while others may experience an acute reaction, and often affect the face, ears, legs and underbelly. These signs include: 

• Coughing
• Nasal discharge that can be clear, white, or yellow 
• Occasional to chronic dry cough 
• Difficult and labored breathing 
• Increased breathing rate
• Nostril flaring
• Swallowing after coughing
• Abdominal effort to breathing 
• Develops a heave line, an increase of the mass of muscles used to breathe out in the abdomen 
• Mucus on the ground of stable or barn
• Exercise intolerance, with a decreased stamina 
• Hives 
• Hair loss
• Skin abrasions
• Crusts and scales
• Reddened skin
• Lichenification, or thickened and leathery skin
• Darkened skin 
• Rubbing on trees, barn doors, and fences
• Biting at affected areas
• Head shaking

An allergy develops when the immune system of your horse becomes sensitized to the allergen, in this case pollen. Repeated exposures cause your horse’s body to overproduce antibodies specific to that invader, which in turn release large amounts of the chemical histamine that cause the symptoms in an allergic reaction.

Some horses seem to be atopic, meaning they have a genetic predisposition to have a hypersensitive response to pollen. Affected breeds include: 

• Dutch Warmbloods
• Oldenburgs
• Morgans
• Paso Finos
• Swedish Warmbloods
• Hackney horses
• Polish Arabians 
• Arabian/Saddlebred crossbreeds

Diagnosis begins with a history of symptoms, including when they appeared. Your veterinarian may also want to know about your horse’s environment and food to try and narrow down the specific allergen that is affecting him. After a physical exam, which includes listening to your horse’s lungs, your veterinarian will run some tests. 

Fluid can be collected from the lungs and analyzed, often with an endoscopy, and a lung function test may be performed. Chest X-rays or ultrasounds may also be taken.

Blood is taken for blood and serum testing, which can often identify the specific IgE antibodies that are circulating in the blood. Skin testing can also be performed, which involves injecting small amounts of common allergens into the skin in intervals. A swelling at the injection site indicates an allergic reaction. Based on these allergy test results, it is possible to narrow down pollen as an allergen that your horse is reacting to. This testing is especially important to help with specific treatments for your horse.

One of the best methods of treatment is allergen-specific immunotherapy, which takes the form of a specially formulated injection based on the results of the allergy testing during the diagnosis. While many horses show a response to the desensitization injections, sometimes beneficial results can take up to a year to manifest. 

Other medications that your veterinarian may prescribe include antihistamines and corticosteroids to help control your horse’s allergic response. Fatty acids may be added to the diet. Inhalant medications, such as albuterol and other bronchodilators, may be used with special masks to relax the airways in your horse’s lungs. Steroids can also be prescribed as low dose inhalants, which may be used for long term management. 

Keeping your horse as removed from the allergen as possible can help to reduce symptoms, and includes ensuring your horse’s stable has good ventilation. This can involve installing a fan.

There is no cure for a pollen allergy in your horse, but it can be managed. You may be given medications, including injections and inhalants, to administer to your horse. 

The most important factor to reducing your horse’s symptoms is to keep him from airborne pollen. While this is near impossible, there are steps you can take to reduce your horse’s exposure. By tracking your horse’s symptoms with spikes in pollen counts, you may be able to isolate the specific pollens your horse is sensitive to. Some management strategies include:

• Ensuring proper barn ventilation
• Keeping your horse inside on very hot, humid days, or days with high pollen counts
• Routinely mow pastures to prevent pollination of the resident plants