Have you noticed that your horse’s stall walls or bedding seem dirtier than normal? Are their tail and hind legs constantly stained? Do you find yourself frequently bathing them to remove these stains?

If you have observed any of these signs, it could be a result of Free Fecal Water Syndrome (FFWS).

Free Fecal Water Syndrome often goes undiagnosed by horse owners. In some cases, a stained tail or hind leg is explained as the horse being “messy” or because they “must have rolled in their stall overnight”.

FFWS is a topic on the rise within the equine research community as the prevalence and awareness of this condition grow. More horse owners are discussing the struggle they face to ensure proper care and welfare for horses with FFWS.

According to veterinarians, this condition is fairly common in horses but very little is known about the causes. There is also limited scientific information available on the proper treatment of FFWS. Most of what we known about how to resolve FFWS comes from anecdotal case reports as opposed to clinical studies.

This article will guide you through what free fecal water syndrome is, its diagnosis, common symptoms, potential causes, and possible treatments that may aid in the reduction or elimination of this condition.

If you suspect your horse is dealing with free fecal water, submit their diet for analysis online and our equine nutritionists can review and help you make changes to better support your horse’s digestive health.

What is Free Fecal Water Syndrome?

Free fecal water syndrome is a condition in which horses experience both solid and liquid phases during defecation. The liquid phase can occur before, during, or after defecation of the solid phase or sometimes occur completely separate from the solid phase. [1][2][3][4][5]

In simpler terms, free fecal water syndrome occurs when the horse releases solid feces, and either before, during, or after this, free water runs out of the anus.

From what is known about free fecal liquid in horses, there appears to be no threat to general health associated with this condition but it does become a constant maintenance issue for owners.

The liquid phase of defecation can cause stains on the area around the anus, hind legs, and tail of the horse. This may require routine washing which has been shown to result in skin irritations and inflammation of these areas. [1][2][3][4][5]

This condition may last a few days, months, or years and may change in severity over time. FFWS is fairly new to the veterinary community however, it is believed to be a reasonably common occurrence. [1]

In humans, there is a similar syndrome referred to as Functional Gastrointestinal Disorder (FGID) or Colonic Motility Dysfunction. FGID occurs when there is dysfunction to the colon causing bowel habits to be irregular, alternating between periods of constipation, regular bowel movements, and diarrhea. [6]

In humans, it is easy to notice when FGID is occurring. Comparatively, it is more difficult for horse owners to notice if their horse is affected by FFWS unless the liquid phase of defecation is directly observed.

Fecal Water Syndrome Diagnosis

Veterinarians approach the diagnosis of FFWS in horses similarly to how they would approach diagnosing diarrhea. However, determining whether a horse has FFWS or diarrhea can be difficult.

Veterinarians usually begin their examination by first learning as much about the horse’s history as possible, asking for details such as: [1]

  • Age, breed, and existing gastrointestinal issues
  • Current feeding program
  • Horse’s daily schedule
  • Any changes in horse’s routine (exercise regimen, turnout times, herd, diet)
  • Stress/anxiety level

Horses that are affected by FFWS usually look healthy and seem to be in good body condition and overall health status. This makes diagnosis a challenge for both veterinarians and horse owners.

Common Symptoms of Free Fecal Water

Free fecal water syndrome appears to be more of a cosmetic and maintenance issue rather than a severe health issue but may signify broader dietary and/or welfare issues. Due to this, symptoms or signs that a horse may be affected by FFWS are usually overlooked.

Some common signs that your horse may have FFWS include: [1][2][3][4][5]

  • Fecal matter soaked on the hind legs, tail and around the anus
  • Increased need to wash areas around the anus, hind legs and anywhere that may have liquid phase fecal matter stains
  • Irritation or skin lesions on areas that require increased washing due to staining from fecal water
  • Dermatitis around the hind legs, dock, or area around the anus
  • Signs of discomfort when defecating feces
  • Extensive tail swishing after defecation
  • Nervous trampling of hind legs after defecation
  • Stall walls and bedding frequently dirty with fecal water
  • Abdominal bloating

Causes of Free Fecal Water Syndrome

There is limited research available on free fecal water syndrome. The true causes, prevalence, and frequency of association with other conditions still require investigation.

It has been suggested that the cause of FFWS includes both internal and external factors. Suggested internal factors include:

Diet Imbalances

In horses, it is essential to make sure the proper type of feed is provided and that is it being fed in the proper amounts. The type of food your horse ingests is largely responsible for how stable his or her fecal material will be.

Diets with high inclusion of concentrates have been reported to cause changes to the characteristics of feces. Concentrates include ingredients such as oats, barley, maize, and bran or commercially made extruded or pelleted feeds.

Horses fed hay with excessive amounts of oats have been found to produce stools that are less well-formed. In these horses, the liquid phase of defecation is more noticeable compared to horses fed just hay. [1][8][9]

Veterinary case reports suggest that many cases of FFWS are reduced or eliminated by implementing dietary changes. [1][9]

Switching the type of forage, changing the feeding schedule, and avoiding excess water-soluble carbohydrates (fructans-sugars) can reduce FFWS symptoms. [9]

Rebalancing the diet to match the nutritional requirements of the horse can reduce or eliminate problems such as FFWS. A balanced diet ensures that the horse is receiving all of the individual nutrients required to be in good health.

Maintaining a balanced diet also ensures horses are not at risk of health complications such as nutrient deficiencies, poor performance, gastric ulcers, and other gastrointestinal issues. [1][9]

If you would like help balancing your horse’s diet, submit their feeding program for evaluation at this link and our equine nutritionists can help make adjustments to your horse’s diet plan.


Another factor believed to contribute to FFWS is dysbiosis, generally defined as an imbalance in the gut bacteria.

Dysbiosis occurs when there is a change in the bacterial colonies that make up the horse’s gastrointestinal tract. Normally dominant species of bacteria (such as those found in equine probiotics) are out-competed by other species that may be pathogenic.

Dysbiosis can have a number of causes including stress, dietary changes, or use of antibiotic drugs. In horses, dysbiosis can result in FFWS, diarrhea, colic, colitis, leaky gut syndrome, gastric ulcers and other digestive health problems. [1][7]

Horses are hindgut fermenters that house a complex and diverse set of microorganisms (bacteria, yeast protozoa, fungi) within the gastrointestinal tract that help them to process large quantities of plant fibers. Fibre fermentation can provide up to 70% of your horse’s energy in the form of volatile fatty acids (VFAs).

The gastrointestinal tract of horses is completely reliant on the balance of these microorganisms to be able to perform and maintain proper digestion.

Changing the feed provided to your horse can significantly change the microorganisms present in the gastrointestinal tract, potentially resulting in impared nutrient absorption and digestive upset. When dysbiosis occurs, the horse’s gut may not be able to breakdown and assimilate nutrients found in feed. [1][7]

Not all bacteria present in the gastrointestinal tract are beneficial. Some bacterial organisms that ferment starch and sugars rapidly can lead to an overproduction of VFAs and lactic acid resulting in hindgut acidosis. [1][7]

The causes of dysbiosis can include sudden changes to feed routine, diet type, and meal size. Dysbiosis in horses can be ameliorated through dietary and management changes.

Some studies report changes in the bacterial microbiota of horses with FWS, but other studies report no changes. [11] Therefore, more research is needed to determine what role dysbiosis plays in FWS.

Inflammation in the Gut

Research shows that FFW occurs more frequently in horses that have experienced an episode of colitis (inflammation of the inner lining of the colon). [21]

Water from the diet is predominantly absorbed in the large intestine. Inflammation of the intestinal wall could impair the absorption of water from the digestive tract, leading to more water being expelled in feces. [21]

Colitis may be caused by bacterial or parasitic infection, excess grain intake, overuse of NSAIDs, antibiotic-associated diarrhea, stress or travel, as well as ingestion of irritants or toxins.

Forage Type

When selecting forages for your horse, it is important to incorporate fibers that have good water-holding capacity.

Grass forages such as regular cut hay can better retain water throughout digestion and hindgut fermentation leading to more solid phase feces being expelled. [1]

Certain types of forages have a weaker ability to retain water. This causes more water to released closer to the end of hindgut fermentation. Alfalfa (lucerne) forages, silage and haylage are examples of feed that are less able to hold on to moisture content. [1]

The practice of feeding wrapped forage such as silage (balage) and haylage may also cause FFWS. [1][7]

Abrupt changes in forage batch, type, or provider have also been reported to precede cases of FFWS in horses. Different forages may have differences in their concentrations of volatile fatty acids, pH values, and lactic acid levels. [1][3][7]

The current research available suggests that forage type and feeding strategy play a role in causing FFWS. Modifying the type of forage being provided may reduce or eliminate FFWS. [7]

Management Factors

In addition to your horse’s diet and gut health, equine management practices can also contribute to free fecal water. Suggested management factors include dental health and exposure to stressors.

Dental Health

Dental problems resulting in difficultly chewing have been proposed as a cause of FFWS. Digestion begins in the mouth with teeth manipulating and breaking down foods to create smaller pieces that are easier for digestion.

Researchers believe that issues affecting dental health could impair the digestion of feeds in the hindgut and potentially contribute to FFWS. [1][7]


The connection between stress and gut health in horses is well-studied. Horses that are in a constant state of stress experience increased intestinal motility and a greater frequency of fluidity in feces.

Free fecal water syndrome may develop in response to a variety of stressors such as: [7]

  • Changes in turnout group/social hierarchy of the herd
  • Feed time competition
  • Changes in stable management (new feed time routines)
  • Extensive training
  • Seasonal changes
  • Stall/reduced turnout anxiety

Intrinsic Factors

Gender, breed, and coat colour have also been proposed as factors to consider when identifying if a horse is affected by FFWS. Certain factors increase the likelihood that a horse will be diagnosed with FFWS: [1][7]

  • Geldings have a higher risk of free fecal fluid compared to mares
  • Paints and greys are at higher risk of free fecal water compared to other breeds; however, this may be due to the fact it is easier to spot on light colours

Treatment of FFW Syndrome in Horses

With the true cause of free fecal water syndrome unknown and limited research available, veterinarians are left with the difficult task of treating affected horses.

Some recommendations to help reduce or eliminate the negative effects of FFWS include:

Environmental Changes

Changes to your horse’s environment can reduce potential stressors such as social stress, feed competition, and turnout group composition and size.

Researchers have found that horses suffering from FFW are more likely to be at the lower end of their social hierarchy. [21]

Simple changes that can reduce stress include reducing the herd size during turnout, bringing the horse in to feed, and maintaining a regular schedule. These practices have had some success in treating horses with FFWS.

Dietary Changes

Ensuring your horse is being fed a balanced diet is the first step to remedying free fecal water syndrome. Consider getting a hay analysis for your horse to identify any gaps in the nutrients provided.

When transitioning to a new forage, make the change gradually to avoid digestive disturbances. An equine nutritionist can help you select the best forages to support gut health in your horse.

Mad Barn provides a free and easy way to analyze your horse’s diet by filling out this quick survey. Our nutritionists can help to rule out any dietary factors that may be causing FFWS.

Fecal Microbiota Transplantation (FMT)

Fecal transplantation (bacteriotherapy) is a new topic in the equine industry, but its prevalence in human medicine has been growing for the last decade.

Veterinarians are increasingly discussing the use of FMT to treat issues in the gastrointestinal tract such as FFWS. The procedure involves transferring fecal material from a healthy donor that does not have any gastrointestinal diseases into the gut of the patient.

Implanting beneficial gut bacteria into the patient is believed to restore a healthy balance to the microbiome and help eliminate bad bacteria that was upsetting the gastrointestinal tract. [10]

Multiple studies have examined the effects of FMT as a treatment for free fecal water in horses. One study found an improvement in fecal consistency in horses with FFW 14 days following FMT. [10]

Another study saw improvements in fecal consistency for all horses 3 days after treatment. However, in this second study only 50% of horses were improved at 2 months following treatment which suggests the treatment may not have long-term effects for all patients. [10]

Probiotics and Prebiotics

Probiotics and prebiotics are dietary supplements that promote a healthy colony of bacteria and microorganisms within the gastrointestinal tract.

Probiotic supplements work on a similar philosophy as FMT by supplying the gastrointestinal tract with beneficial bacterial microorganisms that have a positive effect on the horse.

Prebiotics are growth-substrates, such as indigestible fibers, that stimulate the growth of probiotic bacteria.

Probiotics and prebiotics have been used to successfully address other types of gastrointestinal complaints in horses, but they have not been well studied for FFWS. Based on their efficacy for resolving diarrhea, colitis, and other gut problems, it is proposed that they may also help horses with fecal water.

There have been anecdotal case reports from horse owners who have seen benefits from feeding probiotic supplements to their horses with FFWS. In particular, Mad Barn’s Visceral+ supplement and Optimum Digestive Health have been used with positive results.


Visceral+ is Mad Barn’s most powerful gut health supplement. Visceral+ is designed to help maintain stomach and hindgut health and support the function of the immune system.

Visceral+ bacterial probiotics and prebiotic ingredients like MOS (mannan-oligosaccharides) to nourish the hindgut bacteria and restore balance to the entire digestive system. Ingredients like glutamine, magnesium, and lecithin also help to support the integrity of the intestinal lining.

In horses with FWS, we recommend feeding Visceral+ for 2-3 months at a serving size of 80 grams per day to take care of any major imbalanced in the gut. Following this period, switching your horse to our Optimum Digestive Health supplement will help to maintain a balanced hindgut environment.

Visceral+ Ulcer Supplement for Horses


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  • Our best-selling supplement
  • Maintain stomach & hindgut health
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Optimum Digestive Health

Optimum Digestive Health is an equine supplement targeting hindgut health. It is designed to support the fermentation forages and reduce levels of harmful bacteria that may be in the hindgut.

ODH is formulated with both pro-and-prebiotics in addition to yeast, toxin binders, and digestive enzymes that support digestive function and a healthy microbiome. Optimum Digestive Health provides comprehensive support for the entire gastrointestinal tract and help to reduce the risk of digestive upset.

ODH may be particularly beneficial in reducing the risk of fecal water syndrome when making changes to your horses diet. The ingredients in this product may help the microflora adapt more quickly and efficently to forage changes.

Optimum Digestive Health Equine Supplement

Optimum Digestive Health

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  • Prebiotics, probiotics & enzymes
  • Support hindgut development
  • Combats harmful toxins in feed
  • Complete GI tract coverage

More research is needed to determine the causes, prevalence, and effective treatments of free fecal water syndrome in horses. If your horse is affected by this condition, it is important to ensure that their overall gastric health is in the best condition it can be.

Examining the diet and your horse’s daily routine for factors that can affect gut health is a vital first step in addressing FFWS. Submit your horse’s diet for analysis online and our equine nutritionists can help you.

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  1. Lindroth. K. Free faecal liquid in horses. Faculty of Veterinary Medicine and Animal Science. 2020:65
  2. Lindroth, K.M., Johansen, A., Båverud, V., Dicksved, J., Lindberg, J.E. & Müller, C.E. (2020). Differential defecation of solid and liquid phases in horses – descriptive survey. Animals 10 (1), 76.
  3. Lindroth, K.M., Dicksved, J., Pelve, E. & Müller, C.E. Faecal bacterial composition in horses with and without free faecal liquid – a case control study. Sci Rep 11, 4745 (2021).
  4. Lindroth, K.M., Dicksved, J., Vervuert, I. & Müller, C.E. Chemical composition and physical characteristics in faeces from horses with and without free faecal liquid – two case-control studies (manuscript).
  5. Lindroth, K.M., Johansen, A., Lindberg, J.E. & Müller, C.E. Feeding and management of horses with and without free faecal liquid – a case-control study (manuscript).
  6. Chang, L., Toner, B.B., Fukudo, S., Guthrie, E., Locke, E.R., Notron, J.N., and Sperber, D.A. Gender, age, society, culture, and patients perspective in the functional gastrointestinal disorders. Gastroenterology. 2006: 130:1435-1446.
  7. Kienzle, E., Zehnder, C., Pfister, K., Gerhards, H., Sauter-Louis, C. & Harris, P. (2016). Field study on risk factors for free fecal water in pleasure horses. Journal of Equine Veterinary Science. 44, pp. 32-36.
  8. Kienzle, E., Pohlenz, J., & Radicke, S. (1997). Morphology of starch digestion in the horse. Journal of Veterinary Medicine Series A. 44(1?10), pp. 207-221
  9. Lopes, M.A., White II, N.A., Crisman, M.V. & Ward, D. L. (2004). Effects of feeding large amounts of grain on colonic contents and feces in horses. American journal of veterinary research. 65(5), pp. 687-694.
  10. Theelen, J.P.M., Luthersson, N., Laustsen L., Edwards, E.J., Kujawa J.T., Smidt, H., Van Doorn, A.D.(2019). Free faecal water: what do we know and can equine faecal microbiota transplantation be used to manage this issue? European Equine Health &Nutrition Congress. 9th edition.
  11. Schoster, Angelika et al. Dysbiosis is not present in horses with fecal water syndrome when compared to controls in spring and autumn. Journal of Veterinary Internal Medicine. 2020: 34, 4, pp. 1614-1621.