Foal heat diarrhea is a condition involving transient diarrhea in young foals, lasting for a few days up to two weeks. Foals with heat diarrhea do not have any systemic illness. [1][2]

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. [2]

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). [3]

Common signs of foal heat diarrhea include watery feces, skin irritation, and hair loss where diarrhea has made contact with the skin. [3]

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. [3]

Therapeutic strategies for foals with diarrhea include providing electrolytes and applying creams and ointments to areas of affected skin. [4]

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. [5]

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. [1]

However, researchers now recognize that the condition affects foals regardless of the mare’s milk composition. [6] Orphaned foals and those raised separated from their mother can develop scours. [2]

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. [1]


Diarrhea is one of the most common diseases in young foals and may occur in over half of all foals until the age of weaning. [7][8][9]

Foal heat diarrhea is estimated to affect between 49 and 80% of foals. [7][8]


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. [3]

Newborn foals are born with an immature gut microbiome. [16] Foals aged 2 to 30 days have significantly less diverse microbial populations in their gastrointestinal tract compared to older animals. [16]

A newborn’s microbiome is primarily comprised of bacteria from the Firmicutes phylum. [16] 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. [16]

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). [3]

Secretory Diarrhea

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. [6]

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. [6] These secretions may overwhelm the undeveloped colon, which is not able to absorb the increased volume of fluid and electrolytes. [6]

In this study, the fecal pH was alkaline, and the concentration of dissolved particles and volatile fatty acids decreased with the onset of diarrhea. [6]

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. [10]


Foal heat diarrhea varies in severity between cases. Common signs of this condition include:

Watery Feces

Foals that are nursing normally produce manure with a pasty consistency and yellow color. [4] Those with foal heat diarrhea will produce feces that is yellow to brown coloured and mildly loose to slightly watery. [4]

Foal heat scours is generally mild and self-limiting. [4] In contrast, foals with diarrhea caused by an infection often have profuse and persistently watery diarrhea in combination with additional symptoms such as fever. [4]

Hair Loss

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. [4]

Referred to as skin scald or scours scald, this condition is a result of skin irritation due to diarrhea. [4]


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.

Vital Signs

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. [11]

Pulse: Newborn foals have a heart rate ranging between 80 to 100 beats per minute. [11] Foals that are a few weeks to a few months of age have pulses ranging from 60 to 80 beats per minute. [11]

Respiration: Newborn foals have respiratory rates that range from 60 to 80 breaths per minute. [11] Older foals have resting respiratory rates ranging from 20 to 40 breaths per minute. [11]

Feeding Behavior

Foals normally nurse several times an hour in the early days of their lives. [4] 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. [4]

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. [3]


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.

Hydration Status

Diarrhea can cause an excessive loss of water from the body. If your foal is dehydrated, a veterinarian should be consulted immediately.

Signs of dehydration can include lethargy, depression, and pale or very dark pigment in the gums due to poor capillary refill when pressure is applied to these tissues using your finger. [12]

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. [4]

Distinguishing from Other Illnesses

Diarrhea is a major cause of morbidity and mortality in foals. [9] 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. [13]

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 [13]
  • Bacterial: E. coli, Salmonella spp., C. perfringens, C. difficile [13]
  • Parasitic: C. parvum, Ae. hydrophila, Giardia, and Eimeria [13]


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.

Electrolyte Supplements

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.