Many owners see those telltale bumps and attribute them to insect bites when, in reality, they’re hives—the end result of a complicated allergic response.
A case of hives also referred to as urticaria, can be frustrating for the horse, the owner and the treating veterinarian. Hives can show up minutes to hours to days after exposure to an inciting agent, may or may not be itchy and can appear nearly anywhere on a horse’s body.
Although hives are one way allergies can manifest in the horse, hives are not always caused by allergies. What makes hives particularly challenging is that many, many things can cause hives, such as insects, inhaled pollens, ingested foods, administered medications, direct contact with a wide variety of substances, and even hot or cold temperatures, pressure and exercise.
Though they can occur during any season, equine hives, or urticaria is a common problem with horses during the summer months. Hives present as circular bumps covering large areas of the body. They are sometimes accompanied by itching. Hives are a sign of disease, not a specific disease itself.
Sometimes contact with a substance or material such as a fly spray or bedding may cause hives. There are so many possibilities that finding the cause is often difficult. It is helpful to note if any product or care changes brought the hives on. Removing potential elements one at a time and waiting a minimum of 1 – 2 weeks to see a difference is a time consuming and unrewarding method of determination. For the one-time occurrence of hives, you might never discover the incriminating source. However, if hives recur, you might be motivated to track the allergen. Start by mentally reconstructing any changes in diet, environment, medications, vaccinations, or stress factors that occurred in recent months. Provide your veterinarian with a list of suspicious items or events. Another diagnostic technique, albeit expensive and time-consuming, uses intradermal allergy testing to try and isolate an allergic source from pollens (plants, bushes, and trees), molds, grasses, weeds, dust mites, insects, and farm plants. The horse should be pulled off medications (steroids or antihistamines) at least 10-30 days prior to testing.
Managing horses with hives includes:
Your first plan of attack should be to make the horse as comfortable as possible, which might require use of medications such as steroids and antihistamines, supplements such as omega-3 fatty acids and MSM, and a skin-care regimen such as cool rinses. Next, it is necessary to determine the initial cause of the hives. In some situations, skin eruptions can be linked to a recent deworming, antibiotic administration or similar event. This acute reaction may resolve on its own and, if the product is avoided in the future, might never return. In other situations, a horse will break out with no obvious changes in his lifestyle or management and improve as long as he receives dexamethasone or prednisone, only to have bumps and welts re-appear as soon as the medication is discontinued.
Nutting out the cause
Consider: Is it now bug season? Did you use a new bedding? Has the turnout program changed? Was the horse bathed with a new shampoo? Your veterinarian might suggest avoiding or reducing exposure to insects, fly spray, a certain brand of shavings, a specific grass lot or a brand of topical product while the horse’s skin recovers. Then, you may like to re-apply the possible cause of the hives under controlled circumstances by adding one possible cause at a time. If hives immediately recur, this process of elimination worked. If not, it will be necessary to cast a wider net and keep searching for the culprit, even if it requires keeping a daily journal of observations.
In addition, the vet may need to perform diagnostic tests such as skin scrapings, cultures, impression smears and biopsies to rule out conflicting skin conditions such as infections.
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