Clinical management of gastroduodenitis and equine gastric ulcer syndrome grade IV of unknown origin in an Arabian mareA two-year-old Arabian filly was referred with symptons of colic. Clinical examination revealed signs associated with endotoxemia. Ultrasonographic examination of the abdomen demonstrated severe distention of the stomach and distended loops of small intestine with reduced motility. With nasogastric intubation, eight liters of hemorrhagic reflux were retrieved. Gastroscopic examination showed a severe degree of gastric ulceration scored as equine gastric ulcer syndrome (EGUS) grade IV. Based on these findings, EGUS and gastroduodenitis (GD) were diagnosed. Initially, the horse was treated using parenteral pantoprazole, which was supplemented by adding enteral ranitidine and sucralfate when the horse ceased refluxing. The horse was discharged eleven days after presentation with a 75%-healing of the gastric ulcers. A control gastroscopic examination was performed thirty days after discharge showing a 90%-healing (EGUS Grade I). To the authors’ knowledge, this is the first case report in which pantoprazole in combination with ranitidine and sucralfate has been used to treat a severe degree of gastric ulceration.