Diarrhea and Fecal Water Syndrome in Horses

courtesy of SmartPak

Frequent, loose stool in horses can range from mild, chronic diarrhea that is a nuisance but does not affect the horse’s overall health to severe, acute diarrhea that is a medical emergency. A related condition is the newly described Fecal Water Syndrome or Free Fecal Water, in which a horse passes normal, solid manure separately from fecal liquid. This article describes the signs and symptoms of these three conditions in the horse, possible causes, veterinary diagnosis, and methods to treat and manage them.

Acute and Chronic Diarrhea in the Horse

“Diarrhea” is defined as an increase in the frequency, volume, or fluid content of stools. For reference, horses normally pass manure about 8 to 12 times per day. “Acute” refers to a condition that comes on suddenly, lasts a short time, or rapidly progresses. Since acute diarrhea in the horse can quickly become very serious, even life-threatening, it is a good idea to contact the veterinarian right away.

“Chronic” refers to a condition that persists over a long period of time. As far as diarrhea in the horse, some experts consider frequent, loose stool that lasts at least 7 days to be chronic, for others the cutoff is 2 weeks, and some use 1 month as the threshold. Depending on the cause, some horses with chronic diarrhea remain bright and healthy with good appetite and hydration. That is, the prolonged watery, soft stool does not affect the horse’s weight, energy, or overall health and just causes the hind legs, tail, and environment to be constantly soiled. However for others, chronic diarrhea can result in a sick horse that gets worse the longer the condition continues therefore a vet needs to be involved.


Diarrhea in the horse can develop from a wide variety of both infectious and non-infectious causes including:

• Bacterial infection (Salmonella, Clostridia)
• Viral infection (Equine Coronavirus)
• Parasitic infection

• Change in diet
• Antibiotics
• NSAIDs (non-steroidal anti-inflammatory medications) such as bute
• Inflammatory Bowel Disease or IBD
• Sand ingestion
• Stress (such as from trailering or competing)
• Gastric ulcers
• Toxins
• Secondary to another disease or condition such as peritonitis
• Altered organ function such as chronic liver disease or heart failure
• Cancer

In some cases, chronic diarrhea develops after a bout of acute diarrhea.

Signs & Symptoms

Because diarrhea in horses is an increase in the frequency, volume, or fluid content of feces, a mild case can be just a few more manure piles in a day than normal that are more “cow plop” in consistency than the regular, formed fecal balls. If the horse is showing no other signs of illness, this might be a case of “wait and see.”

However, if the diarrhea is profuse and watery – or worse yet explosive or “pipestream” – or is accompanied by other signs of illness such as colic, dullness, little to no appetite, fever, or purple to red gums instead of the normal pink color, then the horse should be examined by a veterinarian right away.


Getting to the bottom of why a horse is experiencing frequent, loose stool can be challenging for veterinarian and horse owner alike. It begins with a thorough history:
• Age and any existing medical conditions along with medications
• Current feeding program (hay or pasture, grain, supplements)
• Turnout and exercise schedules
• Recent changes to diet, workload, or management
• Exposure to new horses or new facilities

In addition, owners should be prepared to give a complete accounting of the current problem. This includes when the loose stool first started and what it looks like, what other signs have been observed, a list of all treatments given and the result, whether any other horses in the barn or herd are sick, and similar information.

After a complete physical examination, the vet may recommend certain tests to help rule in or rule out specific causes. For example, bloodwork can be used to: assess red blood cells for the presence of anemia and white blood cells for the presence of infection, measure the degree of inflammation in the body, evaluate the health of organs such as the kidney and liver, and check for acid-base or electrolyte abnormalities. A number of fecal tests may be performed, such as bacterial culture, counting parasite eggs, and looking for the presence of sand.

Vets may also perform an abdominocentesis or “belly tap” to directly check the fluid in the abdomen, while ultrasound and radiography (x-rays) are sometimes used to image specific structures. The horse’s stomach and duodenum could be “scoped” or visually assessed and samples taken of the tissue at the same time. Samples or biopsies can even be taken of rectal tissue during a palpation. An intestinal absorption test –which measures the efficiency of sugar absorption from the intestine as a gauge of how well the intestinal cells are doing their job — is simple and easily done at the barn.

Treatment & Management

The primary cause of frequent, loose stool in horses is never fully discovered in well over half of all cases, meaning therapy is mainly supportive in nature and not specific. Therefore, the choice of therapy — and the location in which it’s provided – may depend more on whether the horse is suffering from an acute bout of severe diarrhea or a mild, chronic diarrhea. In order to replace fluids and electrolytes; address pain, inflammation, and endotoxemia; and promote repair of intestinal tissue, it may be necessary to refer an extremely sick horse to a hospital for more intensive, round-the-clock nursing care and observation. For more in-depth information regarding treatment, complications, and prevention of colitis, one potential cause of diarrhea, read our article here.

When the goal is simply to re-establish normal intestinal microflora and encourage regular, firm manure, better results may be achieved in the horse’s usual home. Probiotics, prebiotics, and yeast are commonly recommended at this stage, as are dietary trials that either eliminate suspect feedstuffs or add in components known to be easy for horses to digest and absorb. It can take weeks, months, or years of experimenting to find the right combination of forage, grain, supplements, and medication to maintain formed fecal balls for some horses with chronic diarrhea. In others, a satisfactory solution is never found or only provides temporary relief and the loose stool returns. In these cases, owners must make sure the horse has ready access to water to maintain hydration and that they have a system for keeping the hind legs and tail clean so as not to attract flies or cause skin lesions.

Fecal Water Syndrome in Horses

Fecal Water Syndrome (FWS) in horses — also called Free Fecal Water (FFW) — is considered to be a separate condition from diarrhea/loose stool. It is defined as a horse passing fecal liquid separately from normal, solid manure and can occur before, during, after, or completely independently of defecation. Newly recognized by the veterinary community, it is believed to be fairly common. FWS is mainly a cosmetic problem for horse owners as the hind legs and tail are chronically wet and filthy, but continual soiling with fecal water can also lead to skin lesions.


The underlying cause of FWS in horses is not known at this time and there are many theories as to why some horses develop it. A group of researchers in Germany set out to explore some of the proposed theories and discovered that neither dental disease nor a heavy parasite burden seemed to be associated with FWS. However, it was found to be more likely to occur:
• in horses of low rank or “pecking order” in the social hierarchy of a herd
• in winter when subordinate horses were confined to a smaller space, leading to anxiety
• in geldings vs mares, which are usually more dominant than geldings
• in paint horses

More studies are needed to examine the role of stress, nutrition, and other factors in the development and management of FWS.


Most veterinarians approach the diagnosis of a horse with FWS similar to one with diarrhea or loose stool. That is, they start by taking a thorough history from the owner, then perform a complete physical examination with special emphasis on the digestive system, and finally may recommend specific tests to evaluate the health of the horse in general and the GI tract in particular. It can be helpful to confirm the presence of soiled hind limbs and tail as well as dirty stall walls and bedding. While on the farm, the vet may want to walk through the regular feeding and management programs including turnout and herd status.

Treatment & Management

Although there is no standard treatment or set of recommendations for the care and feeding of horse suffering from FWS, all potential causes for disruption in the GI system should be addressed, including social stress. This could mean changing up or reducing the size of the turnout group, making gradual adjustments to the diet with the input of a veterinarian and nutritionist, and testing the effects of various medications and supplements one at a time on the passage of fecal water. For example, some horses seem to respond to less “bulk” or long-stem forage in the diet, to adding omega 3 fatty acids for a normal inflammatory response in the gut, and to the stabilizing effects of “baker’s yeast” or Saccharomyces cerevisiae.

At the same time, it is important to keep the skin on the hindquarters clean and dry to prevent sores. The vet involved may have practical suggestions for keeping the skin healthy such as winter blanketing tips, summer fly management, tail solutions, and the best products to use for cleaning and coating.


Diarrhea in the horse that is sudden and severe can be life-threatening, while chronic diarrhea and Fecal Water Syndrome can be frustrating in terms of both the horse’s health and appearance. For all situations in which a horse’s manure is not normal, it is a good idea to involve the veterinarian sooner rather than later so that the serious or simple causes can be ruled out and a systematic approach taken to improving defecation.