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 has only fairly recently been given its name; however, it is believed to be a reasonably common occurrence. [1]

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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. However, these horses were fed an extremely high amount of oats (4.55 kg / 10 lb) twice per day. It is unclear if more commonly fed amounts influence manure quality. Increased FFW was not reported and their colonic contents lacked the low viscosity free water phase found in horses fed hay only. [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 and sugars) might reduce FFW. [9]


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

Dysbiosis occurs when there is an imbalance 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 or there is a decrease in the number or diversity of organisms.

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

The number and diversity of microorganisms, and therefore the ability to easily adapt to diet changes, is markedly decreased in older horses, putting them a greater risk of digestive dysfunction. [6]

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). Absorption of VFAs, along with sodium and bicarbonate, is required for normal water absorption in the colon. [8]

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

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. A common scenario that causes dysbiosis is a switch from pasture to hay, or from a soft hay to one that is older and more stemmy. [12]

Some studies hypothesize changes in the bacterial microbiota of horses with FWS, but other studies report no changes. [11] However, fecal transplantation from unaffected horses can be helpful. [13]

Forage Type

Manure from horses with FFWS has less water-holding ability. [1] Other than the obviously high water-holding ability of soluble fibre, very little is known about the relative water-holding capacity of various fiber types.

The practice of feeding wrapped forage such as silage (baleage) and haylage may be associated with FFWS. However, not all horses respond the same. Other horses on the same property can be eating the same forage without issues. In addition, the digestibility of hay, haylage or silage made from the same cut of grass has been shown to be identical. [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 and the ability of the horse to ferment them. [1][3][7]

The current research available suggests that forage type and feeding strategy play a role in FFWS. Modifying the type of forage being provided may reduce or eliminate FFWS but there is no single solution that reliably works for all cases. [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 have hypothesized that issues affecting dental health could impair the digestion of feeds in the hindgut and potentially contribute to FFWS. However, studies to date have failed to find a difference between affected and normal horses, or to demonstrate any benefit from dental care. [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 could theoretically involve 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

A survey of owners of horses with FFWS in Germany revealed a high percentage of the horses were group-housed and at the very bottom of the social hierarchy. In addition to causing stress, this would mean the other horses in the group get the most palatable and digestible portions of the offered feed. [7]

Intrinsic Factors

Some studies have identified geldings as more likely to have FFWS than mares. Horses that have grey or paint coat colours were also more affected. [1][7]

However, other studies have failed to confirm this and these are likely not causally related to FFWS.

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. [10]

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 should be the first step to supporting gut health. Consider getting a hay analysis for your horse to identify any gaps in the nutrients provided.

Choose a hay that has adequate protein and is not excessively fibrous. Grass hay harvested at an early growth stage will likely meet these criteria.

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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, also known as transfaunation, has been used to treat diarrhea in horses for over 40 years.

Veterinarians are increasingly discussing the use of FMT to treat issues in the gastrointestinal tract such as FFWS. The procedure involves transferring the fluid from filtered 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 improve bacterial numbers and diversity. [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 underlying factors upsetting the microbiome had not been addressed. [10]

Probiotics and Prebiotics

Probiotics and prebiotics are dietary supplements that provide beneficial bacteria and microorganisms.

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.

Psyllium husk fiber powder is a prebiotic with very high soluble fiber content that can benefit many horses with FFWS. It is best administered after wetting the powder to make a gel. [14]


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Optimum Digestive Health is an equine supplement targeting hindgut health. It is designed to support the fermentation of forages and provide beneficial organisms.

ODH is formulated with both pro- and pre- biotics in addition to yeast and toxin binders that support hindgut function.

If you have ruled out foregut issues, ODH is a good option for supporting the hindgut.

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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.
  2. Lindroth, K.M. et al. Differential defecation of solid and liquid phases in horses – descriptive survey. Animals. 2020. View Summary
  3. Lindroth, K.M. et al.Faecal bacterial composition in horses with and without free faecal liquid – a case control study. Sci Rep. 2021.
  4. Lindroth, K.M. et al. Chemical composition and physical characteristics in faeces from horses with and without free faecal liquid – two case-control studies. BMC Vet Res. 2022. View Summary
  5. Lindroth, K.M. et al. Feeding and management of horses with and without free faecal liquid – a case-control study. Animals (Basel). 2021. View Summary
  6. Theelen, M.J.P. et al. The Equine Faecal Microbiota of Healthy Horses and Ponies in The Netherlands: Impact of Host and Environmental Factors. Animals (Basel). 2021. View Summary
  7. Kienzle, E. et al. Field study on risk factors for free fecal water in pleasure horses. J Equine Vet Sci. 2016.
  8. Argenzio, R.A. et al. Interrelationship of Na, HCO3, and volatile fatty acid transport by equine large intestine. Am J Physiol. 1977. View Summary
  9. Lopes, M.A. et al. Effects of feeding large amounts of grain on colonic contents and feces in horses. Am J Vet Res. 2004. View Summary
  10. Theelen, M.J.P. et al. 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. 2019.
  11. Schoster, A. et al. Dysbiosis is not present in horses with fecal water syndrome when compared to controls in spring and autumn. J Vet Intern Med. 2020. View Summary
  12. Cavallini, D. et al. When Changing the Hay Makes a Difference: A Series of Case Reports. J Equine Vet Sci. 2022. View Summary
  13. Lausten, L. et al. Free Faecal Water: Analysis of Horse Faecal Microbiota and the Impact of Faecal Microbial Transplantation on Symptom Severity. Animals (Basel). 2021. View Summary
  14. Stewart, A.J. Free Fecal Water Syndrome in Horses. Merck Vet Manual. Accessed December 20, 2023.