Muck bucket and rake in hand, each day’s cleanup gives you a measure to monitor your horse’s well-being based on the number and quality of the manure piles. You are probably highly aware of the amount collected in the bucket or wheelbarrow. Perhaps you notice that the manure is not completely normal-shaped “horse apples” but rather has a watery component along with formed fecal balls. And, then you investigate your horse’s hind end and find manure stains where there should be none. Is this a cause for concern?
One cause of a horse showing tell-tale signs of manure soiling of rump and rear legs is due to free fecal water syndrome (FFWS). Diarrhea tends to be frequently passed loose or watery feces lacking in solid fecal matter. In contrast, a horse experiencing FFWS defecates a relatively solid pile of manure followed by wet feces or liquid. The liquid phase doesn’t always come just at the end, it may also pass at the beginning of or during defecation.
What are the Consequences of FFWS?
Mostly, FFWS is a cosmetic issue that makes it difficult to keep the horse clean. The most likely significant effect is irritation or scalding of skin (dermatitis) from manure adhered to the hind limbs, tail, and perineal region around the anus. Some horses seem irritated while passing manure, likely due to fluid dripping on their legs.
Another concern is that liquid manure staining the legs and hind end may attract increasing numbers of flies, adding to the irritation. Mares with poor perineal conformation are at greater risk of fecal contamination of the vaginal vault.
Horses with FFWS often show no other clinical signs, often having a good appetite, no difference in weight or body condition from their herd mates, and minimal discomfort aside from irritation/tail swishing when voiding fecal water. The amount of water lost does not appear to be substantial enough to cause clinical dehydration.
There also doesn’t seem to be a strong association with development of colic and FFWS in the literature. However, one study (Kienzle) notes that about 25% of horses with FFWS had previous history of colic compared to the general population colic incidence of 3.5 – 10.6%. In horses recovering from colitis (colon inflammation) from a variety of causes, there may be a prolonged period of free fecal water during the recovery period, but this is secondary to the primary colon disease and not the cause of colon disease.
What are Possible Causes of FFWS?
Leaky Gut Syndrome?
“Leaky gut” in horses results from altered intestinal permeability due to damage to tight junctions between intestinal cells that line the hindgut. Tight junctions act as gatekeepers between gastrointestinal contents and the systemic circulation. Such permeability allows the abnormal movement of ions, nutrients, inflammatory cytokines, and/or intestinal microbes to “leak” into the systemic circulation.
When other causes of excess fecal water have been ruled out, another consideration may be damage to the tight junctions. This can result in increased water loss between these cells into the lumen (cavity) of the colon and cecum along with decreased water reabsorption through the hindgut.
Leaky gut syndrome occurs secondary to issues with intestinal immune function, disturbances in microbiota, acute or chronic inflammatory disease, and mechanical and functional intestinal obstructions. Any irritation to the bowel lining, such as from sand accumulation, long stem or coarse hay, non-steroidal or antimicrobial drugs, can also alter intestinal permeability. However, current studies in horses with FFWS have not shown evidence of leaky gut indicators, such as disturbances in hindgut fermentation, changes in microbiota composition or diversity, or evidence of hindgut acidosis.
Dental Health?
Dental health has been examined as another consideration for FFWS. Excessively long fiber length of forage – greater than 1” in length – is more difficult for hindgut microbes to ferment for appropriate digestion. Effective dentition is important for grinding fiber to digestible lengths less than 1-inch, and issues such as worn or missing teeth, sharp enamel points, or dental arcade imbalance potentially affect the grinding ability of the teeth.
Although compromised forage grinding may affect microbial fermentation, studies on dental health and FFWS provide information: In a study (Kienzle et al), recent dental correction did not change the occurrence of FFWS according to owners of affected horses. Severe dental problems can alter fecal particle size, but another study (Zwirglmeier et al 2013) shows that moderate dental problems don’t affect particle size. Therefore, it is unlikely that dental abnormalities are a consistent cause of FFWS.
Intestinal Parasites?
In regards to a possible effect from infestation with internal parasites multiple studies have not shown any differences in fecal egg counts or deworming strategies between horses on the same farms with and without FFWS. However, diagnosis of certain equine intestinal parasites (particularly small strongyles and tapeworms) is challenging and therefore hard to rule out completely. Encysted cyathostomins (small strongyles) cause inflammation of the lining of the large colon and cecum to potentially alter manure consistency. In the majority of horses with FFWS it does not appear that parasites are the underlying cause, but it’s important to work with your veterinarian to ensure that internal parasites are not exacerbating the condition.
Stress?
Stress elicits a variety of health issues in horses. Stress, both physical and mental, affects the microbiome diversity of horses, and may also increase hindgut motility, with less time for processing of feed material and resorption of water. Stress arises from intense training, transport, excessive stall confinement, environmental stresses, heat stress, herd dynamics and hierarchy struggles in competition for feed and shelter.
Owners of horses with FFWS describe that only 37% occupied a high position in the herd social hierarchy, compared to 58% without FFWS (Kienzle et al). The study authors suggest that a lower position in the hierarchy contributes to increased stress and consequential effects on gut motility. In studies in which gender is associated with FFWS, geldings were more likely to be affected than mares or stallions, it is possible that herd dynamics and social status explain this stress-related FFWS phenomenon.
Intestinal transit time increases with stress, with food and water moving faster through the intestines than they would normally. Consider the horse that produces small frequent amounts of somewhat watery feces from a stressful event like a visit to an unfamiliar environment. The hindgut (colon) of the horse is not only responsible for metabolism and digestion of food, but it also secretes and reabsorbs a lot of water – about 30 liters (~ 8 gallons) per day in a standard pony. Hence, only about 10% of the liquid that enters the equine hindgut makes it into the feces. If feed and liquid move more quickly through the colon, fecal water content may increase. This still doesn’t totally explain a mechanism for FFWS, however, since a study (Lindroth et al 2022) found that total fecal water content of horses with FFWS does not differ from horses without the condition; the difference is instead due to distribution of fluid within the feces.
Seasonal Component?
In the available literature, there is not a proven seasonal component, and many horses have FFWS year-round. It seems to appear most often in winter, and a study (Kienzle et al) reports that 31% of horses had FFWS only during the winter. Winter weather corresponds with increased hay feeding, weather extremes, and reduced turnout time. The stress of extreme weather can be a trigger in some horses while freezing temperatures complicate the ability to keep the horse clean.
Endocrine Effects?
Horses with Cushing’s disease (PPID or pars pituitary intermedia dysfunction) frequently have FFWS that improves with treatment of PPID using medications such as pergolide.
Dietary Influences
Long-stem roughage is often associated with the condition. Some horses have sensitivities to different hay types, with rich alfalfa most associated with the condition. However, individual horses do better on one type of hay verses another. It helps to try a different type of hay, preferably less stemmy than what the horse consumed when the condition developed. At least several weeks is necessary to determine if there is improvement or not, once gut flora adjust to new feed.
A case-controlled survey (Lindroth et al) questioned owners regarding…
