Find out what causes watery feces in horses and whether you should be concerned.

Muck bucket and rake in hand, each day’s stall cleaning gives you a measure by which to monitor your horse’s well-being: The number and quality of his manure piles. You’re probably highly aware of the amount you collect.

Have you ever noticed “horse apples” that are not completely normal, having a watery component along with formed fecal balls? Then you investigate your horse’s hind end and find manure stains where there should be none. Is this a cause for concern?

One reason a horse might have manure soiling his rump and rear legs is free fecal water syndrome (FFWS). Alicia Long, DVM, of the University of Pennsylvania’s New Bolton Center School of Veterinary Medicine, in Kennett Square, explains how FFWS differs from diarrhea: “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, which is then 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?

Jamie Higgins, DVM, Dipl. ACVIM, of Idaho Equine Hospital, in Nampa, notes that FFWS is mostly just bothersome to owners, making it difficult to keep horses—especially show horses—clean. “There are not many significant effects to the horse,” she says, “other than possible 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, Long notes, is liquid manure staining the legs and hind end might attract more flies, adding to the annoyance. “Reproductive health may be affected in mares with poor perineal conformation,” adds Higgins. “They are at greater risk of fecal contamination of the vaginal vault.” 

Horses with FFWS often show no other clinical signs, appetite changes, differences in weight or body condition, or discomfort aside from irritation/tail-swishing when voiding fecal water, says Long. “The amount of water lost does not appear to be substantial enough to cause clinical dehydration,” she adds.

“There also doesn’t seem to be a strong association with development of colic and FFWS in the literature, and this fits with my clinical experience,” she says. However, in one study (Kienzle et al., 2016) the authors note about 25% of horses with FFWS had a 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,” says Higgins