“Allergies are extremely common in horses,” said Katherine Williamson, DVM, a veterinarian with Purina Animal Nutrition. “It’s largely linked to management and their environment,”
Williamson discussed allergy testing and diagnosis at the 2017 Annual Mid-Atlantic Nutrition Conference, held April 6 in Hunt Valley, Maryland.
Types of Allergies
Allergies have several potential causes and are categorized into one or more of four general classifications:
- Insect hypersensitivity;
- Contact allergies;
- Inherited atopy (respiratory, dermatologic); and
- Food allergies (although definitive documentation of food allergies in horses is uncommon).
Just about every horse gets itchy when flies and mosquitoes attack, despite our best efforts to reduce bites. Having a horse with pruritis (skin itching) and skin lesions might indicate allergies, but keep it mind it could also have a parasitic or fungal cause. For this reason, “it’s important to know exactly what you are dealing with,” Williamson said,
The primary treatment for allergies is avoidance of the offending allergen, but it can be difficult to detect specific allergens. Williamson gave some tips for narrowing the search for the problem’s cause (or causes):
- Look for patterns of lesions on the body (what contacts the affected area?);
- Consider if anything has changed (environment, bedding, topicals, feed, etc.); and
- Use the process of elimination to try and determine possible causes.
While your veterinarian might treat your horse’s clinical signs, the cause might remain elusive and clinical signs might recur. Therefore, reliable diagnostic tools are needed to identify allergens.
The intradermal skin test (IST) is the “gold standard” for allergen identification. Concentrated allergens are injected subcutaneously (under the skin), and the reactions are measured to determine what the horse is sensitive too. The primary drawback of IST is that results can be hard to interpret, and an experienced veterinarian is required. In addition, a patch of hair needs to be shaved, which is objectionable to some owners.
In the quest to find a better, easier, cheaper, and faster allergy test, commercial laboratories have offered serum allergy testing (SAT), which has become widely use in veterinary practice. For SAT, the veterinarian draws a blood sample, sends it to the lab, and awaits testing results. However, SAT also has major limitations, most notably that no commercial labs use horse-specific antibodies for testing, and results tend to be inconsistent. This method is also not useful for diagnosing food allergies. Consequently, test results can be difficult to interpret.
To diagnose food allergies, allergy specialists recommend an elimination diet. This involves removing all medications, supplements and concentrates, and putting the horse on a hay-only diet. These items can be reintroduced one at a time. If the horse shows no reaction, the item is likely not a culprit. A veterinarian and nutritionist should help oversee this process.
More research is essential for the development of a reliable allergy test in horses, Williamson said. The ISD remains the gold standard for allergy diagnosis (except food allergies). An elimination diet is currently the only reliable way to diagnose food allergies.
If you suspect your horse is suffering from allergies, take notes about everything he or she comes in contact with, from fly spray to bedding and everything in between, and make note of any reaction your horse has. Relay this information to your veterinarian so you can develop a proper plan of action.