Reading time 15 minutes

Free Faecal Water Syndrome (FFWS) is not just an annoying cosmetic problem because a sticky black tail simply looks unattractive. There is a tangible health problem underneath that should not be taken lightly. Unfortunately, there is no single cause for FFWS, just as there is no magic cure for it. Although FFWS is one of the diseases of civilisation that are becoming increasingly common, it has not yet been thoroughly scientifically investigated. What we know so far about possible causes and triggers, and how you can localize and remedy them in your horse, can be found here in 5 points:

Feeding haylage

Feeding haylage continues to enjoy great popularity, as the advantages – simpler production and storage – are obvious for the stable owner. Unfortunately, however, ensiled forage is not suitable for horses by nature. The ensiling process is a lactic acid fermentation, comparable to the production of sauerkraut. Lactic acid bacteria process the sugar contained in the grass (and starch from seeds) into what its name suggests: lactic acid. This acidifies the silage so that a pH value below 5 is reached relatively quickly. In such acidic pH ranges, so-called dormancy occurs, i.e. nothing grows here. The bale can then be stored in this form. To achieve such a low pH value quickly, the silage must be rich in sugar, low in fibre and relatively moist. Just then it can create the optimum anaerobic climate for the lactic acid bacteria. Such silage is not recommended, as the grass base is not suitable for horses and at the same time large quantities of lactic acid bacteria are introduced into the intestine with each feeding, which colonise there and lower the pH value in the horse’s large intestine. Acidosis in the intestine (“hindgut acidosis”) causes inflammation of the intestinal mucosa and is now regarded as one of the main causes of various diseases of civilisation such as FFWS.

For haylage, grass is therefore used that has already grown for a long time, just as it would be used for harvesting hay. This reduces the sugar content and increases the fibre content. Good for the horse, bad for lactic acid bacteria. In addition, the silage is left to dry for a long time. However, if dry, stalky silage is used, there is a high risk of air pockets. The lactic acid bacteria don’t like this, but the mould does. If haylage is produced with horse-friendly raw material, clean ensiling rarely takes place. Most haylage bales therefore only reach pH values of around 6, but this does not result in dormancy. Various bacteria such as Clostridium botulinum or even fungi from the mould family or yeasts can multiply in the bale. Unfortunately, neither we nor the horses can recognise such contaminated bales, as the moisture in the haylage binds the fungal spores and there is therefore no “dust”. In addition, the sour odour masks the mustiness of spoilage. Strictly speaking, you have to send a sample of every bale of haylage to the laboratory and have it analysed for bacterial contamination before it is fed. Otherwise you are not only feeding the lactic acid bacteria, which are still present in excess, into the intestine, but possibly also various other harmful germs.

The risk of poisoning with botulism in particular is omnipresent when feeding haylage. Every winter, entire stables fall ill from this poisoning caused by spoilt haylage. The mortality rate for botulism poisoning is around 95% – once poisoned, the chances of survival are therefore extremely low. Mould is also regularly found in haylage bales. This carries mycotoxins and antibiotics into the intestine, which not only burden the detoxification systems but also severely disrupt the intestinal flora. This, together with the lactic acid bacteria introduced, leads to pH changes in the large intestine and a disturbed fermentation process, which in turn can trigger FFWS due to the associated inflammation of the intestinal mucosa. In particular, horses that have been raised on haylage or whose dams have already been fed haylage usually suffer from such a permanently disturbed intestinal environment that, despite all therapeutic efforts, they can usually only be stabilised at a good level, but are not symptom-free. Therefore, especially in breeding and raising stables, emphasis should be placed on flawless and species-appropriate hay feeding.


Research is currently focussing on stress, as it has a considerable impact on the metabolism. Initially, it is a survival mechanism so that an individual can survive. If stress is triggered—for example, because a wolf approaches the group—the body reacts with hormonal and neuronal signals, particularly the release of adrenocorticotropic hormone (ACTH) from the pituitary gland and, as a result, cortisol from the adrenal glands. Among other things, these hormones ensure that the distribution of blood in the body is changed: away from the intestines and skin and towards the muscles in order to be able to run away as quickly as possible. The immune system is suppressed, as are inflammatory reactions and tissue repair mechanisms. None of this is vital at the moment. In the event of short-term stress, the body thus prepares itself for survival. Long-term, constant stress is problematic, because the body cannot distinguish between “wolf coming round the corner” and “horse being constantly bullied in the group”. Both lead to the same reaction, which only in the latter case lasts much longer, sometimes for months or years, and thus eventually leads to exhaustion of the system. With regard to FFWS, a study has shown that stress alone is sufficient to trigger this condition.

If you talk to horse owners about the subject of stress in their horses, most of them initially react with a lack of understanding. After all, the horse stands around bored in the turnout all day, where is stress supposed to come from? However, stress in horses is much more widespread in our keeping conditions than you might first think. The reasons for this can be manifold. Horses are naturally social herd animals, flight animals and steppe animals, as well as being permanent eaters of lean roughage and real exercise junkies. Our keeping conditions, on the other hand, are usually orientated more towards the needs of humans: closed stables without a “horizon”, clipping plus the use of winter blankets, small winter turnouts, either kept individually or in overcrowded paddocks, keeping horses in groups in which no consideration is given to breed, age or other needs, high-performance hay allocated in meals with long breaks. In addition, there is very often bullying in group housing if there are too few feeding spots available, or sleep bullying if there is too little or no bedding available, so that the horses sometimes even start to develop “narcolepsy”. Furthermore, geopathic interference fields can induce significant stress in horses—from the high-voltage power line near the stable to photovoltaic systems on the stable roof and the mobile phone mast near the indoor riding arena. Another factor that is often underestimated is the stress caused by pain. Many older horses suffer from osteoarthritis, which makes their joints ache, especially in winter when the weather is cold and wet. A stomach ulcer is also painful and metabolic imbalances can equally trigger stress if they persist for a long time.

Horse face
It is worthwhile looking for possible stress factors in horses that suffer from faecal water. © Adobe Stock / Alexia Khruscheva

There are many reasons why a horse can become stressed due to the way it is kept or fed. However, it is worth looking for possible stress factors amongst horses with FFWS and – if possible – eliminating those. As this is not always possible, a change of stable is sometimes unavoidable as a therapeutic measure if, for example, the group composition is not working or the horse’s basic needs cannot be met at the stable. And lo and behold: as if by magic, the FFWS often disappears as soon as the stress trigger is switched off, or at least a clear improvement can be observed.

Stomach ulcers

Gastric ulcers used to be dismissed as a ” racehorse disease” because it had long been known that practically every racehorse suffers from them. However, since studies have shown that around 80-90% of sport horses suffer from gastric ulcers, and that around one in two leisure horses is affected, the medical world has begun to take a closer look. The causes of stomach ulcers can be varied and are often due to incorrect feeding (too long breaks from roughage, too much concentrated feed) or stress. This is because stress reduces blood flow to the stomach lining and ensures that it can form less of a “protective layer” against stomach acids. Once a stomach ulcer has formed, it is very painful. The pain itself generates stress, so that the stomach ulcer cannot heal. It is a self-reinforcing cycle. Stress also triggers FFWS in many cases.

Unfortunately, very few horses with clear symptoms show that they are suffering from gastric ulcers. This includes picky eating up to total refusal of either roughage, concentrated feed or supplementary feed, alternating between concentrated feed and roughage or eating breaks in which the horse is either licking the salt block, the metal bars or something similar or even cribbing. Also horses that react sensitively to a new batch of hay, make burping noises or suffer from girthiness or “ticklish tummies” are often affected. In many cases, the permanent stomach pains also cause back tension and the horses often walk stiff under the rider for a longer period of time, meaning that they need a much longer warm-up phase than other horses. But many horses don’t show anything at all, except that they may be suffering from FFWS (which varies depending on the day). You can do a simple test to see whether the FFWS is caused by stomach ulcers: give the horse a teaspoon of alkaline powder (sodium bicarbonate, baking soda, available in any supermarket baking section) with a few soaked hay pellets three times a day. It buffers the stomach acid and thus relieves the pain for a short time. If the symptoms improve, it can be assumed that the horse has stomach ulcers and therapeutic intervention should be taken to prevent long-term damage caused by these ulcers. Feeding alkaline powder is not suitable as a therapeutic agent. Gastric ulcers are a very complex disease process, and it is essential to consider the housing and feeding conditions when treating them. However, experience shows that if the stomach ulcers improve, the FFWS usually disappears too.

Mouldy hay

Mould in feed poses a major challenge for the metabolism. The mould itself cannot colonise the horse’s intestines as it is an “aerobic” fungus, meaning it needs oxygen to live. It is carried through and excreted in the faeces. Its metabolic end products, which enter the horse with the feed, are much more problematic. These include various mycotoxins as well as antibiotic substances. The mycotoxins partially disrupt intestinal homeostasis, but much more problematic is that they are absorbed and place a strain on the horse’s detoxification systems, namely the liver and kidneys, which in turn leads to metabolic stress. Antibiotic substances, on the other hand, directly disrupt the intestinal flora, which can also lead to malfermentation, which can not only lead to acidification of the colon (“hindgut acidosis”), but also to the absorption of malfermentation products and metabolic stress. We often observe that FFWS problems are resistant to treatment as long as contaminated hay continues to be fed. Only after changing the hay does the therapy take effect and the FFWS improves almost by itself. Mould in feed should therefore not be taken lightly.

Mouldy pile of hay
Mould in feed poses a major challenge for the metabolism. © Sanoanimal / Fritz

Incorrect fibre lengths

The speed at which the food pulp is transported through the intestine depends largely on the length of fibres that have entered. When horses are calmly chewing their grass or hay, they produce fibre lengths of between 2 and 5 mm. These fibre lengths ensure an optimal peristalsis and thus nutrient use. The roughage remains in the large intestine for 20-60 hours in order to be optimally utilised. Shorter fibres – for example, when feeding green meal – pass through the digestive tract in a very short time so that they cannot usually be sufficiently utilised. Longer fibres, on the other hand, remain in the large intestine for longer and are transported back again and again as the body tries to extract more nutrients from them. If fibres with a length of 1-2 cm enter the large intestine, they can remain there for up to a week (150-170 hours). This causes considerable malfermentation, which in turn leads to acidification of the large intestine and thus inflammation of the intestinal mucosa. In many cases, FFWS is the logical consequence.

There are many reasons why such incorrect fibre lengths can enter the large intestine:

Hasty eating

If there are too few feeding spots available, feeding is done in short meals with long roughage breaks in between or the feeding time is limited with automatic roughage feeders. The horses will then be placed under stress to shovel in as much roughage as possible in the shortest possible time. It’s like when the boss arbitrarily shortens the lunch break from 30 minutes to 10 minutes – you shovel the food in far too quickly and then you feel sick afterwards. Horses need much more time than we do to chew their roughage thoroughly. It takes a horse an average of 45 minutes (ponies up to 90 minutes) to chew one kilogram of hay sufficiently. This is only possible if there is enough feed, with a sufficient number of feeding spots and enough time for everyone. Hasty eating leads to poorly chewed fibres in the intestines and also causes a lot of stress for the horses. An adequate amount of close-meshed hay nets are a good solution to avoid hasty eating and take the stress out of feeding.

Dental problems

Ideally, the horse’s teeth should wear evenly and thus always have optimum grinding ability. By now, almost everyone knows that this does not work in practice under our housing conditions. Dental ridges, hooks, various waves, steps or other dental anomalies can mean that the horse can no longer grind its food sufficiently. This becomes particularly problematic in old age when the teeth’s ability to grind decreases or teeth fall out due to age. If the teeth do not work naturally, this results in incorrect fibre lengths, which in turn disrupt the large intestine. As a result, it is often observed that the dentist works on the teeth at the front and the FFWS disappears at the back. There is actually a connection. To ensure that a horse can always chew its roughage optimally, its teeth should be checked once a year by a specially trained equine dentist and adjusted if necessary. If more frequent or less frequent intervals make sense for a horse, the dentist will inform you accordingly. Tooth optimisation not only improves feed conversion, but also relieves the horse’s stress and normalises digestion.

Structured chaff in the feed

They are particularly popular with “leisure horse mueslis” and “grain-free diets”. This is chopped hay or lucerne that is added to the concentrated feed. According to the manufacturer, they are designed to promote chewing activity and make it possible to give the horse a generous meal with little energy at the same time. Studies have long shown that such chaff additions do not extend the feeding time and also do not improve the chewing cycle (compared to concentrated feed). The length of the chaff is simply too short for this. Horses need a fibre length of at least 8 cm to be able to chew them properly. Shorter fibres are not chewed, but rather “crushed” between the teeth in the same way as cereals. A grain of cereal can still be shredded well with this crushing motion, but not hay or lucerne fibre. Fibres are broken down during the horse’s closing phase of the chewing movement by the power stroke. This is a pressure-friction movement in which the teeth are moved completely over each other and the fibres between them are grinded by the chewing surfaces of the molars. Short feeds ensure that no power stroke is performed, but rather short, pressing movements without the actual “grinding” of the chewing surfaces. If short fibres are fed, a large proportion of them enter the intestine practically unchewed and lead to malfermentation, as these fibres remain in the intestine for too long. If you want to motivate your horse to eat its concentrated feed more slowly, you should sprinkle it over the hay portion or on the ground – this actually slows down the intake and ensures better chewing activity. If you feed your horse a grain-free diet, you should feed hay and can also give a handful of herbs as a “reward” ( for instance when the other horses get fed or after riding).

More on this topic: Free Faecal Water Syndrome (FFWS): When The Tail Freezes