Excess Fecal Water or Diarrhea?

Veterinarians may get called for horse with chronic diarrhea, and realize once examining that it’s “Excess Fecal Water”. What does that mean and how do we treat this frustrating condition?

What is normal horse defecation?

An average 1000lbs horse can defecate 8-10 times a day, producing over 30lbs of feces each day. It can take up to 72 hours for food to be fully digested and exit as manure. After chewing and digesting grass in the stomach and the small intestine, the feed is fermented in the cecum and colon using a very complicated population of bacteria called a microbiome. The bacteria help break down the plant components, produce volatile fatty acids and some vitamins that benefit the horse. Horses produce manure balls thanks to their efficient colon which absorbs most of the water, and the movement in the small colon as the feces exit the intestinal tract.

The intestinal tract can become ill due to indigestion, imbalance in the intestinal bacteria or microbiome, or infection by viruses, bacteria, or parasites. When the colon is unable to absorb water, the feces end up with more water content. There is a spectrum of colon illness from mild irritation causing excess fecal water, to more significant irritable bowel, and finally clinical diarrhea and systemic disease.

What are the clinical signs of Excess Fecal Water vs. Diarrhea?

The definition of diarrhea is unformed stools with higher water content, and increased frequency of defecation. In order for a horse to develop visible diarrhea, a large portion of the colon has to be diseased to prevent water reabsorption. For this reason, true diarrhea in horses is typically accompanied by systemic illness such as fever, depression, lethargy, poor appetite, and colic. Dehydration is a significant risk, as they can lose up to 60-80L of water a day. Thankfully, diarrhea is less common in horses.

More commonly, the colon is mildly irritated or the microbiome is disturbed. These horses will pass water before, during, or after a normal defecation of fecal balls. This is called free, or “Excess Fecal Water” (EFW) and is believed to be a symptom of indigestion or mild colonic irritation leading to inefficient water reabsorption. EFW has previously been referred to as “chronic diarrhea” however this is a misnomer as the feces generally remained formed and the horse shows no other signs of illness. Horses with EFW are otherwise healthy, with no fever, depression, or poor appetite, however brief moments of cramping, gas colic, flatulence, or poor propulsion while riding may be observed.

Key Difference

A lack of systemic illness or fever is an important differentiating factor between EFW and true diarrhea. Infrequently, a horse with stress, change in environment, or a change in diet/supplements can have very loose, unformed manure. This is still considered a form of EFW if no other signs of illness are seen, and normal formed fecal balls are present thereafter.

In Alberta, there has been a seasonal association with EFW in some horses, with winter hays producing more significant fecal water than the summer pastures.

True, unformed, chronic diarrhea, is associated with the more severe conditions such as irritable bowel disease or (rarely) lymphoma, intestinal melanoma, or Equine Multisystemic Eosinophilic Epitheliotropic Disease (MEEDs) and present with progressive weight loss and lethargy.

How is Excess Fecal Water diagnosed?

Excess Fecal Water is really a symptom, rather than a diagnosis. When it is unclear if the horse is suffering from diarrhea or EFW, a physical examination must be performed to assess the rest of the body and rule out signs of systemic illness. Once the horse has been deemed otherwise healthy, then the underlying cause of the EFW is sought. EFW has been associated with dental abnormalities, stomach and colonic ulceration, stress, changes in herd dynamics, diet changes, and winter hays.

Exams

Oral examination, gastroscopy, abdominal ultrasonography, and even routine blood analysis are often recommended to rule these out. Colonic ulcers have gained a lot of media attention in horses as they have been blamed for everything from colic to poor performance. Unfortunately, we are unable to diagnose colonic ulceration unless they are severe and can be seen on ultrasound, and therefore often treat empirically, just in case they are involved. There are fecal occult blood tests that have been marketed, but many tests have been plagued with inconsistent results, false positive and false negative results making their usefulness questionable.

How do you treat or control Excess Fecal Water?

When an inciting cause, such as novel stress, or food intolerance are identified, EFW can be treated by removing the source. In cases of social hierarchy, changing the herd dynamic may reduce fecal water by allowing low-rank horses (typically geldings) a boss-free environment.

EFW has been anecdotally associated with stored hay, and therefore observed most during the fall and winter months in Alberta. Hay analysis may provide some indication of a nutrient imbalance. A nutritionist is then consulted to recommend nutritional supplements or adjustments to the diet to accommodate for deficiencies. In some instances, switching from hay to a processed hay cube improves EFW as the hay cube is more digestible, has shorter fibers, and has a guaranteed nutrition analysis.

If stomach or colonic ulcers are suspected, treatment with antacids (e.g. omeprazole) or buffers (e.g. AcidFX, Rite Trac, SecureGuard Gold) are recommended. Sucralfate has demonstrated benefit in treating certain stomach and colonic ulcers and is often included in therapies when cramping or mild colic are observed. Hind gut support is provided via delayed-release neutralizing buffer (e.g. Rite Trac, SecureGuard Gold), or pre- and probiotics supplementation (e.g. Equine Choice, Biotic 8).

Pre- and probiotics are the cornerstone of therapy when no other cause can be identified. The original form of probiotic therapy was ingestion of manure by foals, and this technique, called “fecal transfaunation” is still recommended in some instances of persistent EFW or diarrhea. More palatable commercial probiotics are available, and there are many versions on the market. Horses have variable responses to different probiotics however, therefore trial-and-error is required until the right balance is found.

For more information:

Kienzle et al. 2016. Field Study on Risk Factors for Free Fecal Water in Pleasure Horses. J. Eq. Vet. Sci. 44:32-36 |https://doi.org/10.1016/j.jevs.2016.04.098

Theelen et al. 2019. Free Faecal Water: What do we know and can equine faecal microbiota transplantation be used to manage this issue? European Equine Health & Nutrition Conference.

Ertelt & Gehlen 2015. Free fecal water in the horse – an unsolved problem. Pferdeheilkunde. 31(3):261-268.