For the Health of It
Horses develop a number of conditions attributed to allergies , but two of the more common are pruritus ( itching ), which may manifest as rubbing or biting , and recurrent hives . Although biting insects account for many of these allergies , they can also be caused by sensitivities to environmental allergens such as grass , trees , weeds and mites . Environmental allergens should be considered when clinical signs are seasonal and persistent , despite elimination of common causes ( e . g ., biting flies ).
If an environmental allergy is suspected , allergy testing can be a helpful tool to identify the cause . Allergy testing can be performed via two different methods . The first is known as serum or in vitro allergy testing . This test is performed by drawing a blood sample and sending it to a laboratory for interpretation . This route of testing offers several advantages in that a simple blood collection is all that is needed ; sedation is not required and stoppage of ongoing treatments , such as antihistamines or steroids , is typically not necessary . The second method is performed via an intradermal skin test . An intradermal skin test requires the horse ’ s neck to be shaved and multiple injections of different known allergens to be administered under the skin and monitored for allergic reactions . This form of testing offers several advantages over blood testing . Specifically , it can test for more allergens , reactions are detected in the
8 • Walking On
Equine Allergy Testing
Reprinted with permission from Volume 31 , Number 4 of Equine Disease Quarterly
skin where the problem is manifesting and the results are immediately available , unlike blood results that may take a week to receive .
It is important to remember that there are several major limitations regardless of the test performed . First , neither method definitively confirms nor diagnoses a patient with an environmental allergy , because both methods can have false positive and false negative test results . The results should be considered as a guide of potential causes but must be interpreted in context with the horse ’ s clinical signs , region where it lives , seasonality , abundancy of the allergen in the environment and severity of the allergenic reaction . Avoidance to suspected allergens can be impractical and nearly impossible in some circumstances , because most pollens or allergens are ubiquitous or can travel great distances in the air . To use an oak allergy as an example , unless you remove every oak tree for 100 miles around , then removal of oak trees from the pasture where the horse is housed is futile . Finally , the testing modality does not determine future treatment success . To date , studies have not shown one method provides better results when used to guide desensitization therapy ( allergenspecific immunotherapy or allergy shots ).
The main reason for performing allergy tests is to identify possible allergens for inclusion in allergen-specific immunotherapy . These injections are initially given frequently and then spaced over time as the concentration and amount of the allergens is increased . Allergy shots have been shown in numerous studies to be helpful for alleviating allergic conditions in the horse that are triggered by environmental allergens . Most horses that show a response to therapy do so in the first six to 12 months . As previously stated , the route of testing does not impact therapeutic success , but client adherence to treatment protocol is of utmost importance . Given the importance of client participation with allergen-specific immunotherapy , sufficient time should be spent educating and training owners on how to administer injections and identify adverse reactions and therapeutic responses .
CONTACT : Darren Berger , DVM , DACVD