By Roberta M. Dwyer, DVM, MS, DACVPM
Foal diarrhea can be caused by viruses, bacteria, parasites, and non-infectious conditions such as lactose intolerance, or "foal heat" diarrhea. Foal heat diarrhea is due to normal physiological changes in the foal’s gut and usually occurs seven to 12 days after birth. Infectious agents that can cause diarrhea include rotavirus, Salmonella, clostridial organisms, Lawsonia intracellularis and some parasites. However, when it comes to diagnosing diarrhea, it can be difficult to pinpoint a specific cause. If infectious diarrhea has been diagnosed in a foal, it should be isolated from other foals to prevent spread of the infection.
High-quality colostrum is critical to the health of foals. Colostrum contains antibodies that fight off the viruses and bacteria the new foal faces in the first months of life. A blood test done by a veterinarian at 12-18 hours of age will indicate if the foal nursed enough quality colostrum.
The first 18 hours of the foal’s life are critical when it comes to the absorption of colostrum. It is during that window of opportunity that the foal’s gastrointestinal system can absorb the antibodies found in the colostrum. The mare produces antibodies against bacteria and viruses by vaccination or exposure to these organisms in her environment. These antibodies are the primary protection a foal has against harmful germs.
Another critical factor is providing a clean, draft-free environment for newborn foals. This can help reduce the risk of diarrhea as well as other infectious diseases.
Look at the mare’s udder twice daily. A full udder means that the foal is not adequately nursing, getting nutrition, or replenishing its fluids, and is often the first indication of sickness. This should prompt you to closely examine the foal, take its temperature, pulse and respiration and notice if the foal has a tail soiled by feces, indicating diarrhea.
It is important for a veterinarian to evaluate diarrheic foals less than 30 days old because they can develop life-threatening dehydration in as few as six to eight hours. Dehydration occurs quickly in young foals because of their small size and because their gastrointestinal systems are short and do not reabsorb as much liquid from their feces as adult horses. Foals older than 30 days can also develop severe diarrhea which needs immediate veterinary attention.
Treatment for foals with serious diarrhea often consists of intravenous (IV) fluids. This not only replenishes the lost fluids but can help correct imbalances in electrolytes such as potassium, sodium, and chloride. Glucose is also provided in many IV fluid solutions. If serious electrolyte imbalances are not corrected, other organ systems can be adversely affected. Also, intestinal protectants are often used to coat and soothe the gastrointestinal tract; medications for gastric ulcer prophylaxis may be prescribed.
Owners should not reach for antibiotics when they discover a foal with diarrhea. Indiscriminate use of antibiotics can complicate some diarrhea cases by killing off "good" bacteria found in the foal’s gut. Antibiotic decisions should be left to the veterinarian.
Good farm management is key to preventing diarrhea. These practices include the following:
- If you are moving a pregnant mare to a different barn or farm, make sure to transport her four to six weeks before she foals. This time will allow her body to build up antibodies to the local pathogens in her new environment, which will then be passed on to the foal in the colostrum.
- Work with your veterinarian to develop a comprehensive preventive medicine program for broodmares, foals, and other horses on the farm.
- If you are in an area where rotavirus is known to be a problem, discuss vaccination of pregnant mares with your veterinarian. The rotavirus vaccine should be administered to the mare at eight, nine, and 10 months of gestation.
- Isolate new mares and foals for at least two weeks prior to moving them in with the resident population to prevent possible introduction of infectious diseases onto the farm.
- Clean and disinfect the stall in which the foal is born to reduce exposure to bacteria and viruses.
- Make sure the foal gets good-quality maternal colostrum in sufficient amounts in the first 18 hours of life.
- Remove manure promptly from the foal’s environment to reduce exposure to parasite eggs. Do not spread manure on horse pastures.
Roberta M. Dwyer, DVM, MS, DACVPM, is a Professor at the University of Kentucky’s Department of Animal and Food Sciences.
Reviewed and updated by the original author in 2020.