Why does my horse's Free Faecal Water keep coming back? | Equine Science Matters™

Free Faecal Water Syndrome, often abbreviated to FWS or FFSW, is a common concern for horse owners. It is characterised by liquid or watery poop before, after or during otherwise normal-looking droppings. While not usually too much of a problem from an internal health perspective, it can be difficult to keep horses’ hind legs and tails clean, resulting in sore skin and additional fly irritation during summer. It is important to note that diarrhoea is distinct from Free Faecal Water, which can often be caused by disease or infection, and as such should be investigated by a vet.  

No research has identified a specific cause of FWS, although it is likely that a constellation of factors is responsible for its development, with field pecking order, stress, types and amounts of fibre and potentially starch intake all thought to play a role.  

Horses who are lower in the field hierarchy are likely to experience stress on a more frequent basis than their more dominant counterparts and may also have less access to forage if their field-mates move them away. Both situations can alter the gut microbiota, although whether the effect of stress altering the gut motility, lower forage intake, or an altered gut microbiota is behind the FSW in these scenarios was not investigated further in those studies. In any case, ensuring horses have regular access to appropriate forage, as close to a stress-free environment as possible, and perhaps splitting a herd to avoid bullying may all contribute to reducing the risk of recurrence. 

Anecdotally, changes to fibre intake seem to be one of the key contributing factors to FWS and its recurrence. Fibre should always form the backbone of any horse or pony’s diet, and this is most abundantly supplied by the forage. Whether that’s grass, hay, haylage or a mixture depends on the horse’s requirements as well as availability. Although these three types of forage are at first thought to be all different forms of the same thing, in terms of their nutritional profile, they are very different and can also vary significantly within each category. The moisture level and types of fibre are highly variable, and depend on the time of year, weather, growing conditions, and how long the stalks are when they are cut or eaten by the horse. 

Young or relatively short grasses and early cut hay or haylage contain a high level of a type of fibre called cellulose. As well as being a primary fibre source for the bacteria in the hind gut, and therefore a significant contributor to energy intake, cellulose also has an extremely high water-holding capacity. That is to say, its ability to act like a sponge and hold onto the water as it moves through the hind gut and along the colon, ready to be formed into droppings. As digesta moves through the hind gut, it should be an almost soup-like consistency, with the excess water being reabsorbed in the colon as droppings are formed. However, the amount of water that can be reabsorbed in the latter stages of digestion is limited, often more so in older horses, so having a forage that can adsorb and hold onto water helps a great deal with normal dropping formation. 

Longer, more stalky grasses and late or second cut hay and haylage contain proportionally more lignin. This is the almost woody, indigestible part of the plant that provides structure but from which the horse can derive very little energy. While this is useful for horses and ponies who are good doers, lignin has a lower water-holding capacity than forage rich in cellulose. A diet high in this type of fibre will be able to hold onto much less water as it passes through the latter stages of digestion. 

Haylage, regardless of when it is cut, undergoes a process of bacterial fermentation after wrapping. When the haylage is eaten, these fermenting bacteria enter the hind gut of the horse, altering the balance of the existing bacterial population. If this happens suddenly without allowing a period of adaptation, the hind gut microbiota can become unbalanced, lowering the pH of the hind gut. As the hind gut becomes more acidic, the epithelial lining can become slightly inflamed, reducing its ability to reabsorb water.  

Winter comes with many challenges for horse owners, and trying to maintain a consistent diet for our horses has got to be one of the biggest issues we face, especially at the moment, with the lack of forage availability and choice in so many areas of the UK. Variable turnout hours, changing between batches of hay, or swapping between hay and haylage may not seem like big changes to our horses' diets, but they are significant and can have a big impact on our horses' digestive systems, including FWS. As a human example, if someone is used to having a good portion of, say, steamed white cabbage, then one day they ate the same quantity of raw shredded cabbage or perhaps fermented kimchi, the effect on digestion would be highly noticeable, even though they are all versions of the same vegetable. 

Grass has a much higher water-holding capacity than late-cut hay, so if a horse is usually turned out all day and stabled at night with hay, then, due to awful weather conditions, it has to be stabled all day with hay, the water-holding capacity of the forage moving through the digestive system will have reduced significantly. As such, FWS might increase. Similarly, if a horse is used to having hay but the supply is unreliable, they may have to be swapped onto haylage and back again. Although hay and haylage are both conserved grasses, they are nutritionally very different, and such a swap would constitute a drastic dietary change.  

Where horses who are used to a certain turnout routine suddenly have to spend longer stabled, feeding some grass chop to replace a proportion of their hay would help minimise the impact of the change. For horses who need to swap between hay and haylage due to supply issues, the two should be mixed to allow time for the digestive system to adapt. With the difficulties many of us are facing this year, some change is unavoidable. If you would like any help in minimising the impact of these changes, please do feel free to reach out to our registered nutritionists.