While it is not known exactly what causes foal heat diarrhea, researchers believe this condition may occur because the flora of the foal’s gastrointestinal tract is developing. 
It may also result if the foal consumes feed other than its mother’s milk or adult horse feces (a normal behaviour in young foals). 
Common signs of foal heat diarrhea include watery feces, skin irritation, and hair loss where diarrhea has made contact with the skin. 
Foal heat diarrhea should be distinguished from other causes of diarrhea in foals, which involve infection and require veterinary treatment.
There is no specific treatment for foal heat diarrhea and most cases resolve without complications or the need for medical intervention. 
What is Foal Heat Diarrhea?
Also referred to as foal heat scours, this mild diarrhea occurs in horses between 5 and 15 days old. The condition usually lasts 3 days to 14 days. 
Diarrhea refers to an increased frequency of defecation with increased water content in feces. Foal heat diarrhea is transitory and occurs in the absence of infectious illness due to viruses, bacteria, or protozoa.
Foal heat diarrhea was previously believed to be caused by changes in the composition of the mare’s milk during her heat (estrous) cycle following birth. 
A study that analyzed mares’ milk composition post-foaling and during the foal heat period concluded that it was not a causative factor in the development of foal heat diarrhea. 
The exact cause of foal heat diarrhea is unknown. The current leading theory is that the condition is caused by changes within the foal’s gastrointestinal flora due to diet. 
Newborn foals are born with an immature gut microbiome.  Foals aged 2 to 30 days have significantly less diverse microbial populations in their gastrointestinal tract compared to older animals. 
A newborn’s microbiome is primarily comprised of bacteria from the Firmicutes phylum.  The population of microbes changes throughout the first month of life and becomes similar to that of the mother by the time they are 60 days old. 
Scours might be triggered by the introduction of new bacteria to the gastrointestinal system by consuming feed particles and the mare’s manure (a behaviour known as coprophagy). 
A study that analyzed the fecal material of young foals found that changes in their normal bacterial flora resulted in secretory diarrhea, which typically resolved in a few days without requiring specific treatment. 
Secretory diarrhea is caused by secretions from either the small or large intestines and changes in the absorption of water and electrolytes in the gastrointestinal system.
One study concluded that foal heat diarrhea is most likely caused by hypersecretion in the cells of the small intestine in response to diet.  These secretions may overwhelm the undeveloped colon, which is not able to absorb the increased volume of fluid and electrolytes. 
In this study, the fecal pH was alkaline, and the concentration of dissolved particles and volatile fatty acids decreased with the onset of diarrhea. 
Another study involving 30 newborn foals found that Cryptosporidium parvum infection may have some relation to foal heat diarrhea, although this link has not been proven. 
Foal heat diarrhea varies in severity between cases. Common signs of this condition include:
Foals that are nursing normally produce manure with a pasty consistency and yellow color.  Those with foal heat diarrhea will produce feces that is yellow to brown coloured and mildly loose to slightly watery. 
Foal heat scours is generally mild and self-limiting.  In contrast, foals with diarrhea caused by an infection often have profuse and persistently watery diarrhea in combination with additional symptoms such as fever. 
A common side effect of foal heat diarrhea is the loss of hair on each side of the tail and down the hind limbs where fecal material has been in contact with the skin and hair. 
Referred to as skin scald or scours scald, this condition is a result of skin irritation due to diarrhea. 
A veterinarian can provide an accurate diagnosis of foal heat diarrhea by assessing the consistency of fecal matter and examining vital signs, feeding behaviour, weight, and hydration status.
Temperature: Determine if your foal has a fever by taking a rectal temperature. Normal rectal temperatures in foals range between 37.2 to 28.6 degrees Celsius and 99 to 101.5 degrees Fahrenheit. 
Foals normally nurse several times an hour in the early days of their lives.  Nursing frequency typically decreases by the end of the first month of life.
If a foal is not nursing adequately, it may be a sign of illness and the foal should be assessed by a veterinarian. Prompt treatment can save the life of a foal suffering from infectious diarrhea.
A full udder on a mare can indicate her foal may not be nursing normally, getting adequate nutrition, or receiving enough fluids. 
A healthy mare’s milk provides her foal with the energy and nutrients required for growth. It is normal for foals to nibble at grass, the mare’s feed, and the feces of adult horses. 
A healthy foal will gain weight steadily and rapidly. If your foal is losing weight or is anorexic, he/she may be ill and require veterinary treatment.
Diarrhea can cause an excessive loss of water from the body. If your foal is dehydrated, a veterinarian should be consulted immediately.
Foals with infectious forms of diarrhea require urgent veterinary attention. They may need antibiotics, intravenous fluids, and possibly other medications to recover and support healing and gastrointestinal function. 
Distinguishing from Other Illnesses
Diarrhea is a major cause of morbidity and mortality in foals.  It is important to determine the cause of diarrhea in any foal so that the condition can be appropriately managed.
Horses with foal heat diarrhea will not have a fever or other signs of systemic illness caused by infection, such as depression, inactivity, or poor nursing.
Foals with the condition typically nurse well and appear bright, alert, and active despite their condition.
Other non-infectious causes of diarrhea in foals include lactose intolerance and the ingestion of sand or foreign material that irritate the gastrointestinal tract. 
In young foals, infectious diarrhea caused by a viral, bacterial or parasitic pathogen is more serious. Rapid diagnosis and treatment of infections are potentially lifesaving.
The following agents can cause infectious diarrhea in foals:
- Viral: Rotavirus and Coronavirus 
- Bacterial: E. coli, Salmonella spp., C. perfringens, C. difficile 
- Parasitic: C. parvum, Ae. hydrophila, Giardia, and Eimeria 
There is no clinically validated treatment for foal heat diarrhea. In most cases, the condition will resolve on its own without the need for veterinary intervention.
Horses with scours may benefit from the following therapeutic strategies to help support electrolyte balance, promote skin health and reduce the incidence of scours scald.
Providing an electrolyte supplement in water can help to replenish mineral salts that are depleted because of fluid loss from diarrhea.
Electrolytes such as salt also stimulate thirst to help prevent dehydration. Provide your foal with free-choice loose salt.
Regularly cleaning affected areas of skin and hair with warm water and a mild soap may help to prevent hair loss and reduce skin irritation due to diarrhea. Washing the foal’s hind end once to three times per day is likely sufficient. 
The skin and hair should be dried with a soft towel before applying any cream or ointment to it.
Skin Protection Creams
Petroleum jelly or a barrier cream – such as Desitin ointment – can be applied to the skin to help protect it from contact with diarrhea. 
Calamine lotion contains zinc oxide and can help to soothe the skin and promote healing if sores have developed on the skin.
Why Antibiotics Are Not Recommended
Antibiotics are not recommended as a treatment for foal diarrhea because they can interfere with the establishment of a healthy microbial population in the foal’s gastrointestinal tract.
Overuse of antibiotics can also promote antimicrobial resistance and make these drugs less effective in the future.
Probiotics are not currently recommended as a treatment for foal heat scours.
One study found that administering probiotics to foals with diarrhea did not treat the condition and may have prolonged its duration. 
It is unknown whether the probiotics failed to have a clinical effect or if the strains or dose of the probiotics administered were inadequate. 
Foal heat diarrhea typically resolves on its own in a matter of days and without medication.
After the condition resolves, research shows that the fecal composition of affected foals gradually becomes similar to that of an adult horse. 
Most foals experience no lasting effects from foal heat scours. However, it is important to monitor the condition of any foals affected by diarrhea to ensure their health does not deteriorate.
Currently, there is no proven way to prevent foal heat diarrhea.
The following strategies can help support the overall health of foals and prevent illnesses that can cause diarrhea. 
- Develop a comprehensive veterinary care program for broodmares, foals, and other horses at your equine facility.
- If a pregnant mare is being relocated to a different barn, transport her at least four to six weeks prior to the date she is due to foal. Allow sufficient time for the mare to develop antibodies to the pathogens that are present in her new environment so that she can transfer these antibodies to the foal in her colostrum.
- The rotavirus vaccine should be administered to pregnant mares living in areas where the rotavirus infection is known to occur. Your veterinarian may recommend that this vaccine is administered multiple times during the gestation period.
- Isolate new mares and foals for at least two weeks prior to moving them in with the resident herd to avoid introducing infectious diseases to other horses at your facility.
- Ensure the stalls in which any foals are born are cleaned and disinfected to limit exposure to pathogens.
- Have your veterinarian test the first milk produced by mares to determine if it has adequate antibodies in it or have the foals’ blood tested 18 to 24 hours after their birth to assess their level of colostrum absorption. Colostrum is essential in the first 12 hours of life to help provide foals with protection against infection.
- Reduce exposure to parasite eggs by removing manure from the foal’s environment.
You can get a head start on supporting your foal’s gut health by working with an equine nutritionist to come up with a weaning plan and a transition diet. Submit your foal’s information online for a free evaluation by our nutritionists.
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