Foal Heat Diarrhea

Diarrhea is the most common problem affecting foals. While foal heat diarrhea is mild and goes without consequences, infectious enteritis is serious and often fatal.

Foal heat, or "ninth day diarrhea" (which actually occurs form days 6 to 14), affects nearly all newborn foals. The stool is soft, pasty-yellow, and not profuse. The foal appears unaffected, remains bright and alert, and nurses at regular intervals. The diarrhea usually lasts fewer than 7 days.

Since the diarrhea happens to occur when the mare enters her first heat after foaling, it was believed that hormones in the mare's milk caused the diarrhea. In fact, the same diarrhea also occurs in orphan foals. Newborn foals normally eat manure and feedstuffs such as grain and hay. It appears that the ingestion of these substances may upset the flora of the foal's immature intestinal tract and cause temporary diarrhea. Recent studies show that foal heat diarrhoea is most likely caused by hypersecretion in the small intestinal mucosa (the membrane of the four coats of the intestinal wall), which may overwhelm an immature colon that is unable to compensate by increased fluid and electrolyte absorption.

Diarrhea of short duration associated with the foal heat requires little treatment. Keep the foal dry and clean around its tail. Zinc oxide ointment is applied to prevent scalding of the buttocks. Luxatives, purgatives and variety of untested equine probiotic products that are commercially available are not recommended as they will make the diarrhea worse.

Brown horse

Foals with diarrhea may be infected with picobirnavirus.


  1. Horse Owner's Veterinary Handbook, James M. Griffin, M.D. and Tom Gore, D.V.M.
  2. Faecal composition in foal heat diarrhoea.Masri MD, Merritt AM, Gronwall R, Burrows CF. 1: Equine Vet J. 1986 Jul;18(4):301-6
  3. Evaluation of Lactobacillus pentosus WE7 for prevention of diarrhea in neonatal foals, Weese 'JS, Rousseau J., J Am Vet Med Assoc. 2005 Jun 15;226(12):2031-4

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