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 diarrhea, also know as foal heat scours, is a term used to describe diarrhea that occurs in foals between 5 and 15 days of age (1). It is called foal heat diarrhea because the foal's dam usually is experiencing her first heat (or estrous cycle), since the birth, during this time frame. This first heat cycle is called the foal heat. Foal heat diarrhea was originally believed, to be caused by changes within the mare's milk composition during her heat cycle, leading to a transitory diarrhea in the foal. However, orphan foals or even foals raised separated from the mare also have developed diarrhea during this time. A study was performed which analyzed mare’s milk composition during the immediately post foaling period as well as during the foal heat and determined that the mare’s milk was not a causative factor in the development of foal heat diarrhea (2). More likely, foal heat diarrhea is caused by changes within the foal’s GI flora due to introduction of feed and other bacteria due to coprophagy (the ingestion of the mare’s manure by the foal) which was suggested by a study which analyzed the fecal material of young foals (3).
The main distinguishing factor between foal heat diarrhea and other infectious causes of diarrhea (diarrhea caused by bacterial or viruses) 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 are active. Foals with infectious causes of diarrhea most often will be depressed and quiet, they do not nurse well, and they may have a fever. Furthermore, foals with foal heat diarrhea generally have 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 overtly 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 virus. As the foal's normal resident bacterial flora changes, it causes a transitory secretory diarrhea, which resolves in a few days usually without requiring treatment (3).
You often will see young foals during this time period, eating feces from their dam. Although this behavior is not particularly pleasing to watch, it is normal for foals, as we believe this is the way young foals populate their GI tract with healthy bacteria.
Foals at this age, however, can succumb to other, more serious forms of diarrhea; and 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 cover 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, treatment with Bio-sponge® paste, which is composed of a natural clay called Di-Tri-Octahedral Smectite, has been shown in several studies to be effective at adsorption of harmful toxins in the equine GI tract (4) and is what we use most often when treatment for foal heat diarrhea is requested by an owner. Antibiotics are not required for treatment of true foal heat diarrhea.
If your foal has any of the signs of systemic illness, however, or if you are unsure about your foal's diarrhea, your veterinarian should be asked to examine the foal immediately, as foals with infectious forms of diarrhea will need prompt treatment likely with antibiotics, intravenous fluids and possibly other medications to support the GI tract.
As a side note--one of the more obvious signs of foals, that 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 diarrhea contacting the skin. Using petroleum jelly applied on both sides of the foal’s backside, two to three times a day can prevent skin scald. This treatment prevents diarrhea from contacting the foal's skin. 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. Please always cover your hands with disposable gloves and wash your hands thoroughly after handling a foal with any type of diarrhea even foal heat diarrhea. Even with the use of petroleum jelly, washing the foal is usually necessary at least once a day.
Zimmel, D. Proc of Am Assoc Eq Pract Focus Meet 2008: 207.
Johnston RH, Kamstra LD, Kohler PH. Mare’s milk composition as related to “foal heat” scours. J Amin Sci 1970:31; 549-53.
Masri MD, Merritt AM, Gronwall R, et al. Faecal composition in foal heat diarrhea. Equine Vet J 1986; 18: 301-6.
Lawler JB, Hassel DM, Magnunson RJ et al. Adsorptive effects of di-tri-octahedral smectite on Clostridial perfringerns alpha, beta and beta-2 exotoxins and equine colostral antibodies. Am J Vet Res. 2008 Feb; 69 (2) 233-9.
About the Author: Christina Cable, DVM, DACVS, is a 1994 graduate of the University of Georgia's, College of Veterinary Medicine and is a Diplomate of the American College of Veterinary Surgeons. Dr. Cable owns Early Winter Equine, PLLC, a 3-doctor ambulatory equine practice in Lansing, NY.
Reviewed and updated by the author in 2020.