Free Fecal Water Syndrome


It’s as unappealing as it sounds. The horse has normally formed manure but passes extra brown water along with it, staining the tail and hindquarters.

Poor fermentation of highly fibrous hays may cause free fecal water

This is different from diarrhea, where the frequency of passing manure is increased and/or the consistency of the manure itself is more liquid.  Diarrhea is caused by the intestinal tract secreting more fluid than normal (inflammation) and/or intestinal passage rate being increased so that there is not enough time for water to be absorbed normally. Disrupted fermentation can also cause diarrhea.

As gut contents make their way through the colon they become progressively drier and more formed. In the FFW condition, this process is not as complete as normal.

A German study reported FFW was more common in horses low in social status, leading them to propose stress as a cause. However,  those horses would also be the last to eat and would  get the lowest quality available food. FFW also occurs in horses under no stress whatsoever.

I believe the most likely cause is reduced fermentation activity in the large intestine. When organisms ferment food they produce volatile fatty acids – VFA.  VFA are an important source of calories and easily absorbed. It has been demonstrated that absorption of VFA  greatly enhances the absorption of water.

The FFW problem is typically linked to a diet change such as:

  • Switch from pasture to hay
  • Feeding haylage
  • Hay change
  • Too much grain

With hays, high fiber fractions is a common cause and switching to a lower fiber, softer hay often solves the problem. Haylage is probably an issue because the easily fermentible fractions that feed the intestinal microbiome have already been fermented. Too much grain is well documented to disrupt fiber fermentation. What constitutes “too much” will vary from horse to horse but a ceiling of 1 gram of starch per kg of body weight per meal seems to be a safe guideline.  This would be equivalent to 2.75 lbs of plain oats for an 1100 lb horse.

The poor fermentation theory is supported by work done by researchers at Utrecht. They found that transfaunation was very effective. Transfaunation is when fluid filtered from intestinal contents or manure mixed with water is given to the horse by stomach tube.

As above, switching the horse to  a more easily fermented hay may solve the problem. If the horse has poor chewing, try going to soaked pellets or cubes. If these measures are not enough, add a generous serving (1 to 2 cups) of wet pure psyllium husk fiber powder to meals once or twice a day .i  Avoid products with sugar or other ingredients. The horse may also benefit from a high potency probiotic with good enzyme activity .

Horses with FFW are not in pain and appear healthy otherwise but do appear to have compromised intestinal function which could  make them more vulnerable to something more serious. It also poses a grooming challenge and can compromise skin health. Fortunately, it’s usually correctable if you follow the steps above.

Eleanor Kellon, VMD

About Dr. Kellon

Graduate of University of Pennsylvania Veterinary School. Owner of Equine Nutritional Solutions,, industry and private nutritional consultations, online nutritional courses. Staff Veterinary Expert at Uckele Health and Nutrition .
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13 Responses to Free Fecal Water Syndrome

  1. Pingback: Uckele Health & Nutrition My horse has gut issues | ARTICLES

  2. Claire Hammond says:

    When using psyllium husk to help with FWS do you recommend using it every day or for 7 days each month?


  3. Jo Anne says:

    As suggested in one of your articles I’ve put my 19 yr old quarter horse in uckele Absorb All to help with FWS. He has gained about 20 lbs which is concerning. The weight gain is not good as he also has navicular. Thinking I should stop the uckele. Your thoughts?


    • Dr. Kellon says:

      Improving the efficiency of how his intestinal tract works also improves the calorie yield from the diet. What does he weigh and how much are you feeding him?


      • Jo Anne says:

        Thank you for your prompt response. He gets 1/2 qt of nutrena safe choice senior Am/ pm and roughly 10-12 lbs of free choice hay. Sometimes a bit more hay in the really cold weather. I’ve been feeding him this way for years. Never had an issue with significant weight gain. He is roughly 1145 lbs ( I need to tape him again)and 15.2 hands. He gets one scoop of the absorb all am only.


    • Dr. Kellon says:

      Is that 10 to 12 pounds total for the day or twice a day? Have you weighed it?


      • Jo Anne says:

        Hard to say. Others feed him. I give him an 8 lb slow feed bag at night. Others feed him. Honestly it could be more. There is always hay available.


  4. Lori Cymerman says:

    My 16 yr old gelding has FWS.. appears worse in winter.. he has always been a healthy easy keeper QH.. he is on 1st cutting Timothy mix (no pasture in winter ) and is on triple crown senior only at about 3lbs a day . I have tried several supplants including SmartPak and Equisure but nothing seems to help.. it’s just very messy on the back end .. any other suggestions?


    • Dr. Kellon says:

      The first thing I would try is more highly fermentable soluble carbohydrate from Psyllium Husk Fiber. Add 1 to 2 cups per day, which is 8 ti 16 oz by weight . Be sure to wet it before mixing into his feed. He may also benefit from a broad spectrum probiotic to help enhance fiber fermentation . Let us know how he does!


    • Jenny says:

      Hi Lori…my 25 year old mare was suffering for months from unexplained fecal water. She was also on Triple Crown Senior and I tried a few different supplements, never suspecting the senior feed could be an issue. As a last ditch effort, I switched her from the TCS to alfalfa/timothy pellets and the fecal water cleared up almost immediately! My other horses have had no problem with the TCS so there is nothing wrong with the feed, but it might be worth trying with your horse to see if something in it might not be agreeing with her.


  5. Thank you Dr. Kellon for this article. For years I have been concerned and complained to my vet about what I thought was or might become diarrhea, – researched and found nothing to explain it until I read this article. I share your information with out non ridden group: The Non Ridden Equine New England. Most of us are seasoned horse owners and there are a few new to horse ownership. You provide such invaluable information. I also share the article on hay bellies which again makes so much sense and I appreciate your statement that feeding less hay is not the answer. We had a drought in New England this year so I feel fortunate to even have enough hay to feed my horses but feel relieved to have some answers that make sense. Thank you


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