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By Christina Cable, DVM, DACVS

Can you please tell me what foal heat diarrhea is, and what causes it? Some people say it's because of the mare's hormones being transferred in her milk during foal heat, but other people have said that is an old wives' tale.

Foal heat scours (diarrhea) is a term used to describe the diarrhea that occurs in foals between seven and 10 days of age. It is called foal heat diarrhea because the foal's dam usually is experiencing her first heat or estrous cycle (called the foal heat) since foaling during this time. It originally was thought that the heat cycle in the mare resulted in the foal's having diarrhea due to changes in the mare's milk composition. However, orphaned foals or foals raised separated from the mare also have developed diarrhea during this time.

The main distinguishing factor between foal heat diarrhea and other infectious causes of diarrhea--such as rotavirus or a bacterium such as Salmonella--is systemic illness. Foals experiencing foal heat diarrhea are not systemically ill, meaning they do not have a fever, they remain bright and alert, and they continue to nurse well and remain active. Foals with infectious causes of diarrhea usually will be depressed and quiet, they do not nurse well, and they usually have a fever. Furthermore, foals with foal heat diarrhea have a mild, self-limiting diarrhea, whereas foals with infectious causes often have profuse, watery diarrhea.

Veterinarians believe that foal heat diarrhea does not result in the foal's becoming systemically ill because the diarrhea is caused by the changing bacterial flora within the foal's gastrointestinal (GI ) tract, rather than an infection of the GI tract from pathogenic (disease causing) bacteria or viruses. As the foal's normal resident bacterial florae change, it causes a transitory diarrhea, which resolves in a few days without treatment.

You often will see young foals eating feces (coprophagia) during this time. Although this behavior is not particularly pleasing to watch, it is normal for young foals, as we believe this is the way young foals populate their GI tract with the bacteria that are in their environment.

Foals at this age also can succumb to other, more serious forms of diarrhea. There are several ways to tell the difference. First, determine if your foal has a fever. A foal's normal rectal temperature is between 99° and 101.5º F. Second, monitor your foal to make sure he/she is nursing adequately. If the foal is not nursing several times an hour, or if the mare's udder is very full and possibly dripping milk, then most likely the foal is not nursing adequately and is sick. Third, monitor your foal for diarrhea. Foals which are nursing will produce a yellowish, pasty manure (milk feces), which is totally normal. Foals with diarrhea will have more watery, yellow-brown feces that often stains their hindquarters.

Foal heat diarrhea usually results in only mildly loose or slightly watery diarrhea. Foals with other causes of diarrhea often will have profusely watery diarrhea. Foals with foal heat diarrhea rarely need treatment. However, sometimes they require oral or intravenous fluids to replace the fluids they have lost through the diarrhea. Treatment with probiotics or even yogurt can aid in populating the GI tract with normal bacteria in an attempt to help reduce the diarrhea; however, antibiotics are not necessary for true foal heat diarrhea.

If your foal has any of these signs, or if you are unsure about your foal's diarrhea, your veterinarian should be called to examine the foal immediately, as foals with infectious forms of diarrhea will need prompt treatment with antibiotics, intravenous fluids, and anti-ulcer medications.

As a sidenote--one of the tell-tale signs of foals which have had diarrhea is the loss of hair on the foal's backside. This is called skin scald and is a result of skin irritation from the diarrhea. Skin scald can be prevented by using petroleum jelly applied on both sides of the foal's backside two to three times a day. This treatment prevents the diarrhea from contacting the foal's skin and causing scalding. If the foal is already covered with feces, wash the foal's backside and tail with a mild soap, dry with a soft towel, then apply the petroleum jelly or Preparation H. The Preparation H will help soothe the scalded skin. Even with the use of the petroleum jelly, washing usually is necessary at least once a day.

Christina Cable, DVM, DACVS, is a 1994 graduate of the University of Georgia's College of Veterinary Medicine. She and her husband, Mike Ball, DVM, currently operate a private practice named Early Winter Equine Medicine & Surgery in Ithaca, N.Y., doing primary care, consultation, performance horse problems, and clinical pharmacology.