Horses that pass nearly normal manure but with a volume of liquid before or after it might have fecal water syndrome (FWS). This condition can cause discomfort in horses and often leaves horse owners feeling confused and frustrated. A team of researchers recently studied commonalities between horses with FWS to help veterinarians better understand why the condition arises.

“Fecal water syndrome is not considered interchangeable with diarrhea and is prevalent amongst many ages, breeds and disciplines,” said Allison Boehm, DVM, a second-year resident in equine internal medicine at Colorado State University’s (CSU) College of Veterinary Medicine & Biomedical Sciences, in Fort Collins, while presenting her results at the American College of Veterinary Internal Medicine (ACVIM) Forum, held June 19-21, in Louisville, Kentucky.

“Additionally, unlike diarrhea, fecal water syndrome is not considered life-threatening, but the water phase that is expelled during defecation dirties the hindquarters of the horse, causing potential for scalding, irritation, infection, or even lameness in severe cases,” she said. “In addition, the tails of these affected horses are constantly wet, putting them at risk for frostbite in the winter and attracting more flies in the summer.”

Historically, researchers have not identified a definitive cause, and results obtained have either been inconsistent or nonreproducible. So, Boehm said her team set out to identify management factors that might predispose horses to FWS and determine the shedding prevalence of certain pathogens (disease-causing bacteria, viruses, and parasites), namely Salmonella enterica, Clostridium difficile, equine coronavirus, Neorickettsia risticii, Lawsonia intracellularis, Cryptosporidium spp and Giardia.

She conducted a case-control study, collecting fecal samples from 25 horses with FWS and 25 unaffected horses to analyze via PCR and immunofluorescent antibody testing (IFAT) to determine shedding frequencies in horses within 50 miles of CSU and New York City. Also, 117 owners—72 with FWS horses as well as 45 healthy control horses kept on the same properties—completed a 60-question survey. Questions centered around the horses’ diets, housing, access to pasture, social interactions and rank in the social hierarchy, and personality traits. Owners also provided details about any travel history or interactions their horses might have had with other animals. Additionally, they revealed the horses’ preventive care history and previous medical issues, such as GI disease besides FWS, disease unrelated to the GI tract, and musculoskeletal problems. Finally, they answered questions about how FWS appeared in their horses, including duration, frequency of fecal water passage, diagnostics, and treatments.

Boehm said the data revealed:

• Horses with FWS were more likely dealing with simultaneous health conditions, referred to as comorbidities, than the controls. Specifically, she found that pituitary pars intermedia dysfunction (PPID) was six times more likely in the affected group than the unaffected group.
• Horses with FWS were more likely receiving three or more oral supplements.
• They have a history of recent non-steroidal anti-inflammatory drug use (in the past year versus over a year ago) and prior antibiotic use.
• Horses in the FWS and control groups had no apparent differences in the prevalence of infectious disease agent shedding.

“While we cannot determine cause and effect of these findings, we suspect that the diagnosis of PPID and use of multiple supplements may be an effect of the type of owner that owns these horses and their preferred management style, rather than a potential cause of fecal water syndrome,” she said. “Many of the horses in the affected group had multiple diagnostic tests run and were (receiving) up to seven or eight supplements. This, combined with the lengthy questionnaire responses, suggested owners of affected horses were proactive and more likely to pursue testing and treatment whenever possible.”

The positive association between NSAID use in the past year or the use of antibiotics at all with FWS could potentially contribute to clinical signs, Boehm added, but further exploration would be needed to draw a definitive conclusion.

“Unlike previous studies, our group did not find a difference in social interactions between the two groups of horses, and we did not find any difference in breed or sex,” she said, “and while there was no difference found in infectious agent shedding between the groups, serial testing may reveal otherwise.”

Boehm acknowledged a small sample size, owner self-reporting, an ambiguous definition of FWS, and wordy and imprecise questionnaire responses as limitations to the study. Veterinarians in attendance asked about metronidazole—an antibiotic that many FWS horses have received at some point—and noted the drug remains on the list of factors to examine more closely.

Take-Home Message

Boehm’s results suggested veterinarians might encounter FWS more often in horses managed a certain way. While she didn’t find any differences in pathogen shedding between affected and unaffected horses, repeated testing might be needed to detect intermittent shedding potentially linked to FWS.