An eleven month old filly was referred to the Research and Teaching Hospital of the Faculty of Veterinary Medicine at the University of Tehran. The animal presented a three-week history of diarrhea and previous treatment had had failed to effect a recovery. Based on the history, clinical findings and results of laboratory investigations, it was assumed that a gastrointestinal disorder was affecting the filly. After exclusion of other possible etiologies, Brachyspira spp. became the most likely causative agent. Despite supportive therapy in hospital, the clinical condition of the filly deteriorated over the course of eleven days and the animal died of inanition and consequent multiple organ dysfunctions. Subsequent pathological investigation confirmed a Brachyspira spp. infection of the gastrointestinal tract. This report is believed to be the first equine case of Brachyspira-associated gastroenteritis.

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