Allergy Testing
Horses
Allergies and asthma have been a frustration for horse owners for years.
Anything seems to set the horses off; new feeds, dust, shampoos, even some
drugs can cause the hives, runny nose, and itchiness associated with
allergies. Heaves, or asthma, is a common respiratory complaint in these
same horses, and the two diseases combine to present a diagnostic and
treatment challenge for the veterinarian and owner.
Allergies stem from a variety of sources and are grouped into categories,
including contact (shampoos, fly sprays, toxic plants), feedstuffs (oats,
corn, alfalfa), inhalant (pollens, molds, dust), and drug-induced.
Identifying the allergen is frustrating at best in most horses. Often, trial
and error is the only method for determining which food or topical
medication is the source of the symptoms. Environmental allergens such as
dusts or molds are nearly impossible to eliminate in this manner and we are
left with moving the horse to a completely new environment or continuing to
medicate indefinitely with antihistamines. The ideal treatment is difficult
to prescribe until we are sure of a definitive diagnosis.
There are few tests available to definitively identify the source of an
allergy in a horse. Skin testing is commonly considered the gold standard in
humans and small animals, but it is difficult to administer and evaluate in
the horse. Often, a board-certified veterinary dermatologist must run a
minimum of three to five of these tests daily to claim accuracy and
reliability of the test results.
So, rather than skin testing, another option for identifying allergens is
through blood testing. This type of test measures the amount of
Immunoglobulin E, or antibody, in the blood to each tested allergen. Thus,
if the horse has developed an allergy to oats, his IgE levels to oats will
be higher than those in a normal horse and he will have a stronger reaction
to the test medium. Blood allergy tests are not without controversy however,
as they can result in both false positives and false negatives, especially
in horses that have been exposed to particular allergens but aren't showing
clinical symptoms of allergy. The advantages of blood testing include ease
of performance and ready availability, and with careful interpretation a
blood test can be quite useful in identifying exact causes of allergies.
