Rotaviral diarrhea is caused by a double-stranded RNA, non-enveloped virus of the family Reoviridae, genus Rotavirus. This virus is one of the most common causes of foal diarrhea in horse breeding centers around the world. Infectivity and severity of disease generally decline with increasing foal age. It is not considered to be a cause of diarrhea in horses over the age of six months.