Fecal Water Syndrome in Horses

What is Fecal Water Syndrome?

A horse with fecal water syndrome (FWS), also referred to as free fecal water, will have manure that is normal in consistency but also expel fecal water. Often times fecal water will be expelled directly after manure but in some horses the fecal water may be expelled before or as manure is passing or even expelled completely by itself.

Fecal water syndrome is sometimes confused with diarrhea but these are not the same issue. In horses with diarrhea, the manure itself will be more liquid than usual.

How Does Fecal Water Syndrome Impact the Horse?

Horses with FWS don’t normally display any other symptoms of sickness or unthriftiness, but fecal water does make a mess. Fecal water will often coat the tail and hind legs of the horse. This is unsightly and can also lead to skin irritation as well as draw flies during the summer months.

What Causes Fecal Water Syndrome?

The underlying cause of FWS is unknown at this time although researchers have ruled out several potential causes for FWS.

One theory was that unhealthy shifts in the microbial population that lives in the hindgut, known as dysbiosis, may cause FWS; however, when comparing the microbial community between horses with FWS and those without FWS, no differences were found (Schoster et al., 2020).

Studies have found that poor dentition and high parasite loads did not contribute to the development of FWS (Kienzle et al., 2016).

Horses were found to be more likely to have FWS if they had a low social rank in the herd, and geldings were at greater risk of having FWS than mares. Mares may be at lower risk because they are often higher in social rank than geldings.

Fecal water syndrome has been reported in many breeds and is more common in the winter. The increased occurrence of FWS in the winter that then resolves during the summer months, suggests that the composition of forage (grass vs hay) may play a role in the development of FWS in some horses but more research is necessary to understand this relationship.

What Can I Do for My Horse if it Has Fecal Water Syndrome?

It is difficult to identify a single strategy to help horses with FWS because the underlying cause is unknown at this time. As with any horse, a focus on a balanced total diet is recommended. Provide good quality forage at a minimum of 1.5% of body weight per day, a concentrate designed to fill in the nutritional gaps in hay and add calories as-needed, and free access to clean water is the best place to start.

While dysbiosis doesn’t appear to be the underlying cause of FWS, ensuring that total digestive health is supported is warranted. Further, some horses with FWS respond well to Constant Comfort® Plus. There may be other underlying gastro-intestinal issues that are supported by Constant Comfort® Plus that have not been identified yet by the horse owner or vet.

My anecdotal experience is that some horses with FWS are very sensitive to the maturity or “steminess” of hay. These are often individuals that do not experience FWS when their diet is comprised mainly of fresh grass but have issues during the winter months while on hay. Focus on finding a hay that is very soft and digestible. When evaluating hay by hay analysis, hay with lower NDF and ADF values will be less irritating to the digestive tract.

Fecal water syndrome can be a frustrating issue. If you need assistance in developing a feeding plan for your horse, please contact us.


Kienzle, Ellen, et al. “Field study on risk factors for free fecal water in pleasure horses.” Journal of Equine Veterinary Science 44 (2016): 32-36.

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 34.4 (2020): 1614-1621.

Article By: Nicole Rambo, Ph.D.
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