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What's the Bump?!

So you walk out to the barn to throw your pampered horses an afternoon flake of hay and find your favorite trail-riding horse, Buddy, covered from nose to tail in hard bumps!! He was totally fine at breakfast – coat was slick, shiny, and lump-less – and despite his funny appearance he tore right into the flake of hay like normal; he doesn’t seem to be having trouble breathing. So, what happened? Did he get stung by a million bees? Should I, as an owner, be worried?

After speaking with your veterinarian and answering some questions, your veterinarian explains that Buddy’s funny appearance is most likely from an allergic reaction, and that they would be out this afternoon to start treatment.

This is a very common scenario in equine veterinary medicine. The science behind equine immunodermatology is very complex; there is a lot we still do not understand. So for this blog, we are going to focus on what we have available for possible diagnosis and treatment of this complex, but common issue in our patients.

The Investigation

  • Examination by a veterinarian.

  • This is a very important first step. Your veterinarian can help you figure out what might be the source by examining the horse and taking a thorough history. Also, sometimes things are not what they seem – those lumps might be something else altogether, such as a bacterial skin infection. A veterinarian has the appropriate knowledge to decipher whether your horse has hives or something else entirely. It is also important to note that horses rarely have trouble breathing related to skin allergies.

  • Diagnostic Treatment.

  • Sometimes we treat hives with medications without doing any further diagnostics. After successful resolution of the hives, we will have owners monitor for return of the hives and, if it occurs, try to determine a trigger.

  • Exclusion and Resolution or Return.

  • We might start changing/removing items from the horse’s environment, supplements, diet, or routine and see whether the hives return or not. We have a wealth of experience in treating these cases and can provide insight on common triggers.

  • Serum IgE Testing.

  • Blood can be drawn and sent in to a laboratory to measure elevated antibody levels to specific allergens. Based on the results they can determine likely allergens. It is not perfect – we are testing antigens in the blood, not the skin. Clinically, we have had good success with this type of testing and it often gives us a place to start.

  • Intradermal Skin Testing.

  • Performed by a veterinary dermatologist – we typically consult with Dr. Mundell from Animal Dermatology Service. Just as in people, he injects a small amount of antigen for common allergens (like grasses, mites, and molds) under the skin and monitors for a reaction (develops a small welt) to the substance.

Treatment Options

  • Decreased Exposure.

  • This is the most important component of treatment and prevention. Horses that have allergies tend to be allergic to several things. They can handle a certain amount of allergens in their environment. Hives only appear when the amount of allergens are above their threshold. Decreasing exposure to known allergens increases the odds that that horse won’t hit their threshold and break out with hives.

  • Medication.

  • Hives are commonly treated with medications such as anti-histamines, corticosteroids, and/or diuretics, depending on the particular patient and severity.

  • Omega 3/Omega 6 Fatty Acid Supplementation.

  • We often recommend the use of Platinum Performance Skin and Allergy or some other additional source of omega 3/omega 6 supplement.

  • Allergen-specific Immunotherapy (ASIT).

  • The theory is the same with intradermal shots in people – if you expose the patient to low doses of the allergen, low enough that it does not go over their threshold, then they stop becoming sensitive to that allergen. This is recommended in horses where other methods of control have not worked or are contraindicated.

The best person to help you navigate the complicated and sometimes-frustrating realm of equine allergies and hives is your veterinarian. Please contact Tacoma Equine Hospital and schedule an appointment if your horse has a history of allergies or has developed hives. We are here to help!

For more on Insect bite hypersensitivity (IBH), also referred to as sweet itch or a gnat allergy,

read our blog "It's Not So Sweet."


Scott DW, Miller WH: Equine dermatology, Maryland Heights, 2011, Saunders Elsevier.

Kentucky Equine Research Staff. “Food allergy testing in horses”., Nov 3 2014, Accessed 5 Dec 2017.

Kentucky Equine Research Staff. “Improving allergy testing for itchy horses”., Aug 30 2017, Accessed 5 Dec 2017.

ACTT. “Testing and treatment – equine allergy testing”., Accessed 5 Dec 2017.

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