During the spring and summer, some horses, often like some people, can and do suffer from seasonal allergies. It is estimated about 10% of all horses will suffer some type of allergy in their lifetimes, with seasonal allergies being the most common.

Seasonal allergies differ from other causes of allergies, like those arising from food, medications, or even contact allergies, where things like the use of a new shampoo or saddle pad can induce an allergic reaction. For more details on feed allergies, you can reference our Food Allergies or Debunking Myths About Soy articles. Regardless of the cause, the physiological reaction with all allergies is generally the same with some variance on severity.

An allergy manifests itself due to the hyperactivity of the horse’s immune system. The immune system’s role is to defend the body from any foreign substances that have the potential to harm itself. When it detects a substance that it perceives as harmful, it activates by producing antibodies and attacks such. Normally, something like pollen would not be recognized as harmful and an immune response should not be triggered. However, in some horses, their immune systems do interpret it as harmful and respond accordingly.

The substances that cause an allergic reaction are called allergens. At first exposure, the horse’s immune system may recognize an allergen as harmful, but often does not mount a response. Yet, as the horse is exposed to the allergen more often, the immune system does react and over time, its reaction gets stronger and quicker. Some allergic reactions can be quite mild and at times, are not even noticeable to a horse owner. Yet, some allergic reactions can be quite severe and can even lead to paralysis and death. Severe allergic reactions leading to death are quite rare in horses and are usually only observed after the use of a medication. 

Seasonal allergies are those that cause allergic reactions in horses during certain times of year. Typically, these are observed in the spring and summer due to the abundance of potential allergens. Some causes of seasonal allergies include:

  • Biting flies and midges: the saliva in the biting insects such as mosquitoes, stable flies, horse flies and others can induce an allergic reaction in your horse. In severe cases, the allergic reaction is often called sweet itch. This is one of the most common seasonal allergies observed in horses.
  • Mold: it is more common for mold to develop in hay during the warmer months.
  • Pollen: similar to people, horses can develop allergies to certain pollens from a variety of plants.
  • Dust: can be a problem with some bedding types or even hay.

Signs that your horse is having an allergic reaction to seasonal allergies can be:

  • Raised bumps on the neck, flanks and body, often referred to as hives.
  • Patches of hair loss due to intense itching.
  • Coughing due to respiratory inflammation, which can lead to heaves (Recurrent Airway Obstruction).
  • Runny nose.
  • Exercise intolerance or other behavioral changes.

Of the seasonal allergic reactions seen in horses, heaves is often the most worrisome for horse owners. Heaves is the most common lung disease seen in horses and can seriously affect a horse’s health. The inflammation is so severe in some horses that they can have severe difficulty with breathing. If you suspect your horse suffers from heaves, you should contact your veterinarian immediately.

As we have previously noted with feed allergies, identifying any offending allergen(s) to your horse can be quite difficult. With seasonal allergies, most veterinarians will suggest conducting skin tests. This entails the horse’s skin being tested by injections of small amounts of potential allergens (mold, pollen, insect saliva and others) and then observed over a 24-hour period. Any localized immune reaction at the injection site would indicate an allergy to that substance. 

For seasonal allergies, it can almost be impossible to eliminate all offending allergens. However, the goal should still be to at least minimize exposure it. Here are some tips that can be applied to lessen exposure or treat your horse:

  • With barn allergens like dust and mold, horses should be turned out as often as possible.  
  • Soaking of hay can be helpful for horses with dust allergies.
  • If pollen is a cause, keeping the horse stalled during peak pollen season is helpful.
  • For allergies related to insects, a good fly control strategy like that outlined in our Fly Control for Horse Barns is a good first step.
  • Insect repellents, fly masks, and fly sheets can be helpful to horses suffering from insect bite allergies.
  • Topical ointments can be applied to areas of itchy skin to alleviate any irritation.
  • A high DHA omega fatty acid supplement, like Natural Remedy®, can help to alleviate symptoms by decreasing allergic inflammation.

The most important reminder is to always discuss any concerns with any type of allergy with your veterinarian. They will also be a good resource for any questions related to seasonal allergies that affect horses in your area of the world.
 

Chris J. Mortensen, Ph.D.