New Opinions Regarding Free Fecal Water Syndrome

Look for the underlying causes of free fecal water, which might indicate all is not well with the animal.
horse with free fecal water syndrome has his tail washed.
Free fecal water syndrome used to be seen primarily as a management issue: Healthy horses with dirty rear ends and tails. | Bianca McCarthy Photography

Horses affected with free fecal water syndrome (FFWS, also called free fecal liquid or free fecal water) void feces in two distinct physical phases: a solid phase comprising normal fecal balls and a watery liquid phase. Affected horses might void the liquid phase with the solid phase or separately. In some horses, however, FFWS might present with a lack of normal fecal balls, instead resulting in soft feces with a cowpat-like consistency.

“Previously, horses were considered generally to be ‘healthy’ aside from the free fecal water, but opinions on this are now changing,” says Joan Edwards, PhD, a herbivore gut microbiologist who previously collaborated on a FFWS project while at Wageningen University, in the Netherlands. “FFWS used to be seen primarily as just a management issue: Healthy horses with dirty bottoms and tails. It was typically only considered a clinical matter if there were skin-based issues secondary to the constant wetting of the skin.”

In 2021, Edwards and a group of researchers including Nanna Luthersson, DVM, of Hestedoktoren, and Louise Laustsen, DVM, of theVET, published a study in which they examined the intestinal microbiomes of horses with FFWS. 

“The S in syndrome indicates that we don’t really know what is going on with these horses,” says Edwards. ‘’The Danish equine veterinarians that instigated the project, Luthersson and Lausten, now believe that FFWS probably isn’t a condition in itself but, rather, a major warning sign that all is not well with the animal.”

Beyond the Liquid: Other Signs of Free Fecal Water Syndrome

Reported clinical signs in the literature in animals suffering from FFWS include: 

  • Signs of colic.
  • Irritation when voiding feces, such as nervous trampling of the hind feet and extensive tail swishing. 
  • A bloated abdomen and abdominal sensitivity.
  • Lesions on the skin around the anus and inside the hind legs and a dirty tail.

Looking for the Underlying Cause(s) of Free Fecal Water Syndrome

Causes of FFWS still remain largely unknown but could be related to social stress, diet, and low-grade gut inflammation, based on the scant information available in the literature.

Luthersson and Laustsen agree that practitioners should thoroughly assess horses with FFWS symptoms for issues that might have led to FFWS. Four underlying conditions they says they often see in their respective veterinary clinics include:

1. Sand accumulation in the gut. This can occur when horses are kept in sand paddocks, particularly during the winter when pasture turnout is limited.

2. Equine gastric ulceration. In their experience, FFWS tends to resolve after treating the ulcers.

3. Diet. Luthersson and Laustsen emphasize the importance of always assessing diet, particularly when haylage is involved. In fact, in some European countries the condition is commonly referred to as “haylage intolerance” because of the assumed association between feeding wrapped forages and FFWS. “With haylage, every bale is different, so there is a lot of variation as well as potential for hygiene issues,” says Laustsen. “It’s not a constant type of feed either, and that in itself may cause perturbations in the gastrointestinal tract. Those variations in feed might just tip the horse toward a clinical presentation.”

4. Irritable bowel syndrome (IBS) and/or gut inflammation. Although IBS is a potential underlying condition, its causes can be difficult to diagnose—as is also the case in humans.

If one of these four conditions is not causing FFWS, Luthersson and Laustsen agree something else must be going on with the animal that remains to be diagnosed.

“Once the common causes are ruled out, it is difficult to know what or where to start looking next,” says Laustsen. “Could it be metabolic or endocrine issues, perhaps? There is simply not enough information available to answer that question yet.”

The syndrome has also been implicated in horses consuming high amounts of alfalfa, having poor dentition, being over 20 years of age, and experiencing endoparasitic infections. However, Laustsen says she normally she sees FFWS in well-managed horses with good teeth and regular deworming programs.

Recent Research on Free Fecal Water Syndrome

Free fecal water syndrome symptom severity scale
Symptom severity scale (SSS) used for grading free fecal water symptoms in horses from 0 (no free fecal water) to 4 (maximum severity). | Courtesy Laustsen et al. 2021 Animals

As we can see, there is a dearth of information regarding the clinical presentation of FFWS and its causes. Further, data regarding FFWS prevalence and information regarding at-risk horses are lacking.

Veterinary researchers from Sweden and Norway recently conducted a web-based survey of 339 horses with FFWS to try to improve our understanding of the condition (Lindroth et al. 2020). Horse age ranged from 2.5 to 28 years, and Warmbloods accounted for 53% of the cases. Geldings were more commonly affected (57%), and chestnut, gray, and black were the most common coat colors of affected horses.

In the survey, 29% of owners reported tail swishing and nervous trampling while their horses voided feces, while 35% reported their horses showed no clinical signs other than the free fecal water. Horses in the study were not underweight (average body condition score was a 3 on a scale of 1 to 5) or had lost weight. Forty-eight percent of respondents said other horses in the same barn were affected by FFWS, while 52% said theirs was the only affected horse.

The researchers assessed many feeding and management factors, including forage type (i.e., grass haylage, silage, hay, and pasture), concentrates, number of meals offered a day, and amount and type of turnout. Many horses were fed wrapped forages (a common practice in Sweden and Norway), and while some owners indicated FFWS decreased when switching from wrapped forages to hay or pasture, this was not true for all horses. In fact, 25% of horses improved upon changing batches of hay or changing from hay to wrapped forages. Thus, the researchers concluded, “The occurrence of FFL (FFWS) cannot be generally attributed to feeding wrapped forages,” and “Feeding strategy may be of importance but cannot solely explain the presence of FFL.”

Interestingly, the researchers noted, 23% of the horses with FFWS had a previous history of colic, which is higher than the colic incidence reported in other healthy horse populations (3.5-10.6%). They did not present an explanation for this observation, but suggested FFWS could be a “generic symptom from several different conditions of a similar nature.” 

“The number of clinical signs during an FFL episode could also depend on the severity of the condition, which could not be assessed in this study,” they added.

Overall, the study involved a large variety of breeds, ages, disciplines, coat colors, housing systems, and feeding strategies, leading the researchers to conclude any horse can be affected by FFWS. The authors said additional studies are needed detailing the duration, intensity, and severity of FFWS, as well as whether horses had a previous history of gastrointestinal disturbances. They suggested the hindgut microbiota might also play a role in FFWS.

The Fecal Microbiome and Fecal Microbiota Transplants

In their 2021 study investigating whether the hindgut microbiota played a role in FFWS, Laustsen et al. collected fecal samples from 10 horses with a history of FFWS (lasting more than 12 months) and 10 healthy controls selected from the same locations as the FFWS horses. They analyzed samples using standard techniques of amplifying the V4 region of the bacterial 16S rRNA gene. In both the FFWS and healthy horses, the five most common phyla identified were: Bacteroidetes, Firmicutes, Kiritimatiellaeota, Spirochaetes, and Fibrobacteres. These are all considered common or “core” phyla present in the equine hindgut microbiome.

The researchers detected no significant differences in the fecal bacterial communities between the healthy and FFWS horses in terms of alpha diversity or richness. This means the fecal microbiomes of horses with FFWS were as diverse and possibly as “functional” as those of the healthy horses.

Next, Laustsen et al. assessed whether fecal microbiota transplantation (FMT) could help improve FFWS. 

“The rationale was that FFWS could still be related to gut inflammation, but that it may be difficult to see this simply by looking at just fecal samples,” Edwards explains. “There is no evidence to date though indicating a pathogen being the causative agent of FFWS.”

This portion of the study involved the same 10 horses used in Part 1, plus an additional two horses recruited for fecal donation to create the fecal inoculum for FMT. On Day -9 of the study, all FFWS horses began a 10-day course of omeprazole to decrease stomach pH in preparation for receiving the fecal inoculum. A fresh fecal sample was also collected at the start of the study (Day -9). Beginning on Day -4, Luthersson’s team at the Hestedoktoren clinic performed FMT once daily for five days. Fresh fecal inoculums prepared each day were then transferred to the FFWS horses via nasogastric tube. Fecal samples were collected from FFWS horses on Days 0, 7, 14, 28, 84, and 168 after completion of the FMT, and owners were contacted via telephone for follow-up on Day 336. For follow-up evaluations, the researchers used a symptom severity scale (SSS) ranging from 0 (no free fecal water or soft stool) to 4 (constant free fecal water with no episodes of normal feces).

At the start of the study, all horses had an SSS of 3 or 4. The SSS grades were significantly lower by Day 14 compared to Day -9 and remained significantly lower until the final assessment on Day 168. Of the available questionnaires obtained via telephone consultation with the owners, seven of the horses had suffered a relapse of FFWS symptoms to some extent, and one was euthanized due to severe colic.

“Despite the lack of differences in the fecal microbiota of the FFW and control horses, the standardized FMT protocol used in this study significantly decreased FFW symptom severity,” says Edwards. “Thirty percent of the horses experienced complete resolution of symptoms seven days after FMT, but the decreased symptom severity was not significant until 14 days after FMT. However, the responses to FMT treatment varied greatly among the FFW horses.”

The FMT did not affect fecal microbiota composition or diversity in any of the FFWS horses. One possible reason the FMT didn’t change the microbiota but decreased symptom severity is fecal transplants contain more than just microorganisms.

“The fecal inoculates also contain microbial metabolites, and it is possible that alleviation of the FFWS symptoms was instead influenced by the effects of the metabolites, such as volatile fatty acids,” Edwards explains. “For example, butyric acid is known to enhance gut integrity, minimize inflammation, and alleviate leaky-gut-related issues.”

Concluding Remarks

It is important to recognize that FFWS indicates there is likely something clinically wrong with the horse and that FFWS might not necessarily be the underlying cause but rather a generic symptom common to more than one condition.

“If an underlying cause cannot be identified, then consider monitoring the animal over a longer time period and exploring supportive therapy options,” says Luthersson. “In this context, FMT may be valuable to try due to there being evidence supporting its potential to alleviate the symptoms of FFWS.”

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