Free faecal water (FFW) is one of those problems that rarely makes a horse ill but can take over an owner's routine. Tails, hind legs and rugs need constant cleaning, the skin can become sore, and the search for a cause can feel endless. The honest position is that researchers do not yet know what causes it. There is useful evidence on what is and is not associated with the condition, though, and a sensible, step-by-step approach with your vet gives you the best chance of improvement.
What free faecal water is
FFW, also called free faecal liquid or faecal water syndrome, describes a horse that passes normal formed droppings but also passes liquid before, during or after defecation, and sometimes independently of it. A 2019 review prepared for the European Equine Health and Nutrition Congress by Theelen and colleagues notes that affected horses are usually otherwise healthy, that cases are typically isolated within a group, and that no prevalence data exist even though vets in Western Europe see the condition often.
The main welfare concern is the skin. Liquid running down the hind legs can cause irritation, scalding and hair loss if it is not managed. FFW is different from diarrhoea, where the droppings themselves are loose or watery. If your horse's droppings lose their shape, that is a different problem and needs your vet's attention.
What might contribute
The review authors were clear that the limited published literature does not yet allow evidence-based conclusions about the cause, or about how well treatments work. Several studies from Scandinavia have added useful pieces to the picture.
Concentrate and starch
A case-control study by Lindroth and colleagues, published in Animals in 2021, compared 50 pairs of horses with and without FFW on farms in Sweden and Norway. Affected horses received about twice as much concentrate per 100kg of bodyweight per day and had higher intakes of starch and water-soluble carbohydrates. They also received less straw and lucerne. The authors described the differences as small but worth investigating further.
Forage type
Haylage is often blamed, but the evidence is mixed. In the same case-control study, the amount of wrapped forage and general management were similar in both groups. An earlier owner survey by the same research group, covering 339 horses with FFW, found that owners reported improvement when changing from wrapped forage to hay (58%) or to pasture (46%). Owner reports are useful pointers, but they are not controlled evidence.
Gut bacteria
A further study by the group, published in Scientific Reports in 2021, compared the faecal bacteria of the same 50 pairs over three sampling periods. The overall bacterial composition was similar between affected and unaffected horses, although a handful of bacterial groups differed in some periods. That finding is relevant to anyone hoping a single gut supplement will fix the problem.
Taken together, these studies point towards looking at the whole ration and routine rather than searching for one culprit. They are also a reminder that each horse is different: a change that helps one horse may make no difference to its field companion, which is why careful record keeping matters so much.
Practical management steps
Because the cause varies and is often unclear, the most practical approach is to change one thing at a time and keep a record. A simple diary of feeding, forage batches, turnout and how much liquid you see makes it far easier to judge whether a change has helped.
- Involve your vet first. Ask for a check-up, including teeth and a worm control review, so that other problems are not missed.
- Review concentrates and starch. If your horse receives a large amount of hard feed, ask whether the ration could rely more on forage and lower-starch fibre feeds.
- Trial a forage change. Try a different batch or type of forage, such as hay in place of haylage, and introduce it gradually over at least 10 to 14 days, as the British Horse Society advises for all diet changes.
- Feed little and often. Spread forage through the day and avoid long gaps without anything to eat.
- Look after the skin. Clean the hindquarters gently and dry them well. Ask your vet which barrier product is suitable if the skin is sore.
- Keep routine steady. Note whether FFW worsens with changes of field, companions or stabling, and discuss any pattern with your vet.
Our pages on diet changes and turnout and hindgut health explain how to make feed changes safely.
When to involve the vet
Every horse with FFW should be seen by a vet at least once, because the same signs can accompany other problems. Some situations need prompt attention rather than a routine visit.
Our article on the signs of poor gut health in horses covers other changes worth reporting to your vet.
Where probiotics fit
Probiotics and gut balancers are often the first thing owners reach for, so it helps to be realistic. There is no strong published evidence that they resolve FFW. The broader evidence for probiotics in horses is also limited: a 2014 review in the Journal of Veterinary Internal Medicine concluded that evidence for their use in controlling disease was weak, while noting that they are generally regarded as safe and easy to give. The finding that overall faecal bacteria look similar in affected and unaffected horses adds to the case for caution.
That does not rule out a trial. Some owners do see improvement, and a probiotic is a low-risk thing to try once your vet has examined the horse. If you do, treat it as an experiment: change nothing else at the same time, decide in advance how long you will try it and what improvement you are looking for, and stop if nothing changes. Faecal microbiota transplantation has also been discussed by vets as an option, but the 2019 review notes that published evidence for it is very limited.
For help choosing a product, read our guides to equine probiotics and gut balancers, or see how products compare in our best horse probiotics UK roundup.