Stephen White, DVM, Dipl. ACVD, a professor in the Department of Medicine and Epidemiology at University of California, Davis, explained that there are three categories for hypersensitivity (non-insect-bite related) skin diseases. These include food allergies, atopic dermatitis (a predisposition to allergic disease in response to environmental allergens), and contact allergies caused by chemicals, bedding, inhaled dust, or other allergenic agents.

True food allergies are very rare according to White. Those that are seen (real or presumed) are usually tentatively diagnosed using the horse's history which might note an increase in scratching or rubbing or hair loss after a change in feeds or addition of new supplements. Confirmation of food allergies requires feeding a new diet for at least six weeks, eliminating all supplements, and thereby eliciting a decrease in the scratching or rubbing. Final confirmation would require eliciting the recurrence of the scratching or rubbing by challenging the horse with its initial diet.

Initial diagnosis of atopic dermatitis requires a close examination of clinical signs that can include pruritus (the sensation within the skin that causes the horse to scratch or rub itself), alopecia (partial or complete loss of hair), and sometimes pyoderma (bacterial infection of the skin). Depending on the allergens involved, the clinical signs might be noted only in certain seasons.

To give the owner a choice of hyposensitization injections (similar to those used to treat severe "hay fever" in people) White also suggests using intradermal tests (IDT, performed by injecting known allergens into the skin and noting a reaction at the site of injection) or serological allergen tests to determine the actual allergens to be used in the hyposensitization solution.

Contact allergies can also be tentatively diagnosed by changes to the horse's environment, such as new bedding or new topical products (such as ointments, shampoos, etc) being used. Contact reactions are generally localized to the point of contact.

White explained that the horse's complete history, including any home remedies the horse owners might have applied to the skin, should always be taken into consideration when working up the horse.

About the Author

Chad Mendell

Chad Mendell is the former Managing Editor for .

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