Lactose intolerance diarrhea in a Quarter-Horse Foal

Among diarrhea etiologies in horses, lactose intolerance is a less common or undiagnosed condition. Primary (congenital) lactase deficiency has never been diagnosed in foals, and lactose intolerance secondary to bowel injury has never been described in Brazil. Former bacterial or viral infections that cause severe lesions in the intestinal brush border, the area responsible to produce lactase, will be followed by diarrhea due to a lack of enzyme activity. The present report describes the case of secondary lactase deficiency in a 3-month-old foal with chronic watery diarrhea. The foal had been treated with several antibiotics and dewormed without clinical improvement. Complementary exams made were complete blood count (CBC), white blood cell (WBC) count, fibrinogen levels, serum biochemistry (serum proteins, renal and hepatic functions), blood gas analysis, parasite egg count, abdominal ultrasonography, rectal swab culture for three consecutive days and transtracheal wash. Therapeutic diagnosis was performed through administration of 8 mg/kg of lactase (PO), every 4 hours, and stool normalization was observed in about eight hours after starting treatment. Lactose intolerance is an important differential diagnosis of diarrhea in young foals.