Background: Alopecia areata (AA) causes hair loss due to inflammatory changes within and around hair bulbs and lower portions of the hair follicles. Documentation of AA in horses is limited to a few case reports. Hypothesis/Objectives: The aim of this retrospective study was to characterize equine AA by describing patterns in age, sex, breed and lesion distribution in a series of cases. An attempt was made to characterize the long-term course of the disease by surveying owners of affected horses. Animals: Computerized records from 1 January 1980 to 1 July 2011 yielded 15 horses. Methods: Descriptive statistics were calculated for age at presentation, breed, sex, dermatological signs, season when diagnosed and any recurrence of AA. The breed and sex distribution of horses with AA was compared with the equine hospital population during the study period. Results: The prevalence of AA was 0.017%. Appaloosas and quarter horses were the most commonly recorded breeds. The median age was 9 years, with an age range from 3 to 15 years. Alopecia was the primary dermatological abnormality in all horses and commonly affected the mane, tail and face. More than half of the horses presented for other medical conditions. Five of seven (71.4%) owners who returned completed surveys reported a seasonal pattern to the disease, which usually worsened in spring and summer. Conclusions and clinical importance: Alopecia areata is a rare disease in horses, and is typically cosmetic in nature. To the authors' knowledge, this is the first study investigating the epidemiology of equine AA.
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