Fecal Water Syndrome in Horses: How to Tell It Apart from Diarrhea and What to Do About It

Messy stalls. Soiled back legs. Constant manure-stained tails. 

If your horse is passing normal manure balls, but you are also seeing liquid water before, during, or after defecation, you may be dealing with Fecal Water Syndrome.

And it’s more common than most owners realize.

What is Free Fecal Water Syndrome?

Free Fecal Water Syndrome (FFWS) is a condition where a horse passes formed manure balls along with a separate liquid phase.

The manure itself looks normal. The issue is the free water that accompanies it.

It is not the same as diarrhea.

With diarrhea, manure is loose, unformed, and frequently passed.

With Fecal Water Syndrome, manure remains formed. The frustration comes from the liquid that causes staining, skin irritation, and messy stalls.

It can lead to:

• Skin irritation or scalding on the hind legs
• Tail and perineal irritation
• Increased flies in warmer weather
• Frostbite risk in freezing spells
• Ongoing frustration management

What causes Fecal Water Syndrome?

There isn’t one single cause. FFWS is often linked to underlying digestive imbalance.

Fecal Water Syndrome is considered multifactorial, meaning several things may contribute:

• Diet imbalance, especially low quality fiber or high concentrate intake

• Type and moisture content of forage

• Stress
  

• Dental issues that affect proper chewing

All of those factors trace back to one place: the hindgut. Each one has the potential to disrupt the microbial community that lives there and when that community gets out of balance, the colon's ability to regulate water absorption changes.  That is where most of a horse's fiber fermentation takes place, and where a stable, diverse microbial community works to break down forage and regulate normal gut function.¹ When that balance is disrupted, the colon's ability to absorb water properly can change. In horses with FFWS, the water that should be absorbed through the colon wall is instead passing through alongside the manure. The manure stays formed because fermentation is still happening, but the water regulation piece is off.²

Because multiple factors may be involved, there is no single universal solution. What works for one horse may not work for another.
So management matters.

What You CAN Do

Start with foundations.

1. Slow Down Dietary Changes

Any switch in hay, grain, or forage type should happen gradually over 7–10 days to allow the hindgut microbiome to adjust.

2. Evaluate Starch Intake

High concentrate or high starch diets may alter fermentation in the hindgut. Reducing starch where appropriate can improve manure consistency.

3. Reassess Fiber Type

Some horses — especially seniors or those with dental changes — struggle with long-stem, coarse forage. In those cases, incorporating a more digestible fiber source or partial pelleted forage may help.³

4. Support Microbial Balance

When hindgut imbalance is suspected, targeted probiotic support can be helpful.⁴ 

For horses with ongoing FFWS, we often recommend starting with Equine Extra Strength Probiotic Pellets.

Begin with 2 scoops twice daily for 2 weeks
Then reduce to 1 scoop twice daily
Some horses can transition to once daily

The goal is to support normal microbial balance and overall gastrointestinal function while other management adjustments are made.

5. Manage Flare-Ups

During periods of stress, travel, weather shifts, or sudden digestive upset, short-term support can be useful.

Keeping Equine BioClay 5-in-1 Paste on hand allows you to provide additional digestive support during those episodes.  Formulated with adsorbent bioactive clay plus S. boulardii, prebiotics, L-glutamine, and electrolytes, this combination helps address equine gastrointestinal distress. 

6. Reduce Stressors Where Possible

Environmental shifts, turnout time, travel, and weather can all influence gut motility. Even small management adjustments can help stabilize the hindgut.

7. Rule Out Underlying Issues

If symptoms persist, work with your veterinarian to evaluate dental health, parasite load, inflammatory conditions, or metabolic disorders.

The takeaway

When you see formed manure with free liquid, think hindgut balance.

Focus on:

• Consistent, high quality forage
• Gradual dietary adjustments
• Appropriate starch levels
• Stress reduction
• Targeted digestive support

Most improvement comes from layered management and consistency, not a single quick fix.

And if you are ever unsure whether you are dealing with Fecal Water Syndrome or true diarrhea, always involve your veterinarian.