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Free faecal water syndrome in horses

Professor Jo-Anne Murray
PhD, MSc, PgDip, BSc (Hons), BHSII, RNutr, PFHEA University of Glasgow Veterinary School

What is free faecal water syndrome?

Free faecal water syndrome (FFWS) is not the same as diarrhoea. When horses have diarrhoea the whole stool is typically loose or watery, whereas with FFWS the stool is generally normal, but small amounts of water with a very small amount of faeces are passed before, during or after defecation. Horses may also pass this water independently of passing faeces. This can result in the horse’s hindlegs and tail becoming very messy where it can attract flies and also possibly even causing skin lesions. It can be very difficult for owners to keep horses with FFWS clean. It does not appear to be a very common condition and those horses affected by it are generally in relatively good health.

What causes free faecal water syndrome?

Unfortunately, there is no definitive understanding on what causes FFWS; however, some factors appear to impact on this. Coloured horses appear to be at a greater risk of developing FFWS and studies have also reported that geldings are at a higher risk of developing FFWS. Diet has also been suggested to affect the development of FFWS; for example, an abrupt change of forage type (e.g. hay to haylage or vice versa) has been implicated in the development of FFWS. However, this abrupt change can also cause loosening of the faeces, which can also be mistaken for FFWS. The type of forage fed has also been reported to impact on FFWS. Studies have shown that horses fed wrapped forages (e.g. haylage or silage) showed more signs of developing FFWS compared those fed dry hay only. It is important to note, however, that 20 percent of the horses fed dry hay in that study also developed FFWS, highlighting that the type of forage fed is not the only contributing factor in FFWS. Other studies have shown FFWS to improve when horses are turned out to pasture, whereas other studies have shown the opposite where horses kept at pasture full-time have been reported to have a higher incidence of FFWS. Cold water intakes have also been suggested to have a role in the development of FFWS. Therefore, it is unclear exactly how diet impacts on the development of FFWS.

It is also unclear how season impacts on FFWS, with some studies reporting a higher incidence in winter months, some in springtime when horses were grazing spring pastures, others reporting no effect of season on the development of FFWS other than a small number of horses developing FFWS after an abrupt change in weather conditions. There is debate over the impact dental care and parasitic infestations impact on the development of FFWS; some studies have reported both to be involved, whereas others have shown no link between dental care/treatment and parasitic infestation and FFWS. It does appear, however, that FFWS occurs more frequently in horses that have had colitis. There has been a suggestion that social stress 

may impact on FFWS, with many horses at the lower end of the hierarchy having FFWS. Other types of stress, e.g. travelling, may also impact of FFWS. This may be because those horses are not defending their food, which can affect intakes and could also cause the animals to be stressed. Stress is known to increase gut motility and gut motility has been implicated in FFWS; therefore, it is possible that increased stress may impact on the development of FFWS. Gut motility can also affect the amount of fluid in the large intestine, with any inflammatory changes in the gut affecting the enteric nervous system resulting in increased gut contractions that press the water out of the digesta in the gut – leading to FFWS. In fact, horses with FFWS also tend to produce drier faeces than those horses with FFWS, suggesting that this may be a valid explanation. As water is mainly absorbed from the large intestine, another factor that could impact on the development of FFWS is any change in the gut lining, such as chronic inflammation, which may result in decreased water absorption across the gut wall and hence FFWS. The microbes in the gut are also sensitive to dietary changes and other environmental factors, such as stress, and it is possible that these changes may be implicated in FFWS. However, it does appear that the cause of FFWS is multifactorial and does not appear to be the same for each horse. There are, however, risk factors that have been identified: 1) sex, 2) color and 3) social hierarchy.

Management and treatment of free faecal water syndrome

Diet is often implicated in the development of FFWS, albeit it is difficult to ascertain exactly why, but it is important to ensure that your horse’s diet is appropriate. Feeding a horse with FFWS follows the same guidance and principles outlined in maintaining gut health. If you aim to feed in order to maximise gut health this can be beneficial in improving FFWS in horses. Also, at times of additional stress or when making any dietary changes aim to manage this in a way that has the least impact on gut health. For example, ensure adequate forage provision, avoid sudden changes in diet, limit the amount of starch-based feedstuffs fed, and in addition feed forages that have a higher water holding capacity; for example, feeding grass hay results in a higher faecal dry matter compared to feeding haylage as a forage source. Access to fresh grass pasture still remains an unknown in terms of its impact on FFWS; however, it is best to avoid turnout on lush pasture at times of the year when the sugar content of the grass is known to be high (spring/summer). Other than that, very little else is known about how diet impacts on FFWS, but the main advice is to feed a diet high in fibre. Feeding a supplement that is known to be beneficial to gut health, for example yeast, may also be beneficial in terms of feeding a horse with FFWS, but also at time of stress and change, to minimise any potential disruption to the microbes in the gut.

Another approach to treating FFWS is a faecal microbiota transplant (FMT). This is a procedure that involves preparing a faecal suspension from a healthy horse and placing it in the gut of the affected horse. This procedure has been successfully used in humans to treat infections, such as Clostridium difficile, and other conditions that have altered the gut microbiota. There has been some successful use of FMT in horses, but to date there is no standardised approach and not all horses have responded in the same way. It would seem that from the studies that have been conducted to date many horses respond well initially, but the longer-term benefits are less consistent. However, although this approach requires further 

research, it does appear to be promising. However, this should only be undertaken by a veterinary professional.


  • Ensure enough forage is provided to maintain gut health.
  • Feed a dry forage; e.g. grass hay.
  • Avoid feeds that contain starch.
  • Make any dietary changes gradually
  • Consider the use of supplements that can help maintain gut health

Equine Products UK ltd provides the following product that can help support equine gut health:

  • Transvite Excel contains yeast and fructo-oligosaccharides to promote digestion and gut health


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