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By Roberta M. Dwyer, DVM, MS, DACVPM

I am a new owner of a broodmare that just had her first foal, which now has diarrhea. What can I do about it? How serious is it for him? How do I keep this from happening again?

The causative agents for diarrhea can be bacteria, viruses, parasites, non-infectious causes or 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, Rhodococcus equi, 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, that foal should be isolated from other foals to prevent spread of the infection.

One of the main factors that predisposes a foal to develop infectious diarrhea is if the foal received enough high quality colostrum. Colostrum contains antibodies that fight off the viruses and bacteria the new foal faces in the first few weeks of life. A blood test done by your 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 less than 30 days of age 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 organs can be adversely affected, such as the heart and kidneys. Also, intestinal protectants are often used to coat and soothe the gastrointestinal tract; and 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:

* Work with your veterinarian to develop a comprehensive preventive medicine program for your broodmares and foals. 

* 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.

• 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.

• If you are in an area where rotavirus is known to be a problem, discuss vaccination of pregnant mares with your veterinarian. The vaccine should be administered to the mare at eight, nine, and 10 months of gestation.

• Chain harrow pastures where horses are kept to break up manure piles and expose parasites and other organisms to environmental conditions.

• 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.

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 original author in 2016.