Foal-Heat Diarrhea

Foal-heat diarrhea is a normal condition, but owners need to watch for signs of more serious forms of diarrhea.

Foal-heat diarrhea is a term that describes diarrhea (“scours”) that occurs in newborn foals. The condition received its name because it usually occurs while the mare is experiencing her first estrous cycle (called the foal heat) after foaling. Veterinarians still are not sure what exactly causes the condition. Originally, mare owners and veterinarians thought diarrhea resulted from hormonal changes in the mare during estrus or changes in the composition of her milk. However, orphaned foals also develop diarrhea about the same time after birth. Other potential causes that have been investigated include the worm parasite Strongyloides westeri, which is transmitted from the mare’s udder to the foal via her milk. This parasite used to be found in about 90 percent of foals, but the increased use of new dewormers has lowered the incidence to less than 6 percent without a corresponding decrease in the incidence of foal-heat diarrhea. Some owners believe that coprophagy (eating manure), which is common in newborn foals, is the cause, but this is a normal activity designed to help the foal populate his intestine with helpful bacteria. Horses cannot digest the cellulose portion of grass and hay without the aid of bacteria. Because foals are born without bacteria in their intestine, they must acquire them. Their mother’s manure is the best source.

Think you are ready for a new Quarter Horse? Read AQHA's Buying and Owning Your First Horse to make educated choices.

Although the cause of foal-heat diarrhea is still not definitively known, probably the best explanation is that it is the result of rapid maturation changes in the intestinal tract of the foal that interfere with the intestine’s ability to reabsorb fluids. The result is transient, watery diarrhea.

Foal-heat diarrhea usually results in only a mildly loose or slightly watery diarrhea that resolves itself without treatment. Foals remain bright, alert and active and continue to nurse. This is in contrast to infectious (viral or bacterial) diarrhea, which causes the foal to be depressed, refuse to nurse, run a fever and experience profuse, often foul-smelling diarrhea.

Differences in Diarrhea

There are several ways to tell the difference between the two types of diarrhea. First, take the foal’s temperature to see if he has a fever. Foals with foal-heat diarrhea will have a normal temperature of 99-101.5 degrees Fahrenheit, while foals with infectious diarrhea will have an elevated temperature. Second, make sure the foal is nursing. Foal-heat diarrhea foals will nurse, but sick foals will not. And finally, observe the character of the diarrhea. Foal-heat diarrhea usually produces a yellowish, pasty manure, while infectious diarrhea produces a more watery, yellow-brown diarrhea that is often foul-smelling. Foal-heat diarrhea is self-limiting and usually does not require treatment. In fact, antibiotic therapy is contraindicated and should never be used because antibiotics can kill the healthy bacteria and cause severe diarrhea. Because treatment with antibiotics can cause much more harm than good, consult a veterinarian. However, infectious diarrhea can be life threatening and might require antibiotics, intravenous fluids and antiulcer medications. A veterinarian can determine if therapy is indicated and which therapy is best.

AQHA's Buying and Owning Your First Horse gives you all the information to make educated choices about your first Quarter Horse.

Preventing Harm From Diarrhea

One side effect of foal-heat diarrhea is irritation caused by diarrhea running down the foal’s hind legs, which can cause painful scalding of the skin and result in hair loss. Applying petroleum jelly on both hind legs once or twice a day prevents the diarrhea from contacting the foal’s skin. If the foal’s hind legs are already covered with feces, wash the hind legs and tail with mild soap, dry with a soft towel and apply petroleum jelly. Although foal-heat diarrhea is a naturally occurring event, infectious diarrhea is not. Good farm management is key and should include the following:

  • Ensure the foal receives good-quality colostrum in the first 18 hours of life.
  • If rotavirus is a problem in your area, vaccinate the mare during the eight, ninth and 10th month of her gestation. She will pass on protection against the virus in her colostrum.
  • Move mares to the farm where they are to foal at least six to eight weeks prior to foaling. This will give them adequate time to build up antibodies in their colostrum to local pathogens in the new environment.
  • If the mare is to foal in a stall, clean the stall with phenolic disinfectants and bed it with good, clean straw.

Foal-heat diarrhea is a normal condition. However, affected foals should be monitored to ensure that infectious diarrhea or complications do not develop. Before initiating any therapy, check with a veterinarian. Foals are fragile, and unnecessary – or wrong – treatment can cause tremendous damage.