29/05/2026
💩 What your horse’s poo can tell you!
Your horse’s poo is not just waste. It is one of the best daily windows into hydration, forage suitability, fibre fermentation and hindgut health.
Poo is not just leftover hay or grass. It is a mix of water, undigested and partly fermented fibre, gut microbes, fermentation by-products, minerals, mucus and gut secretions. This is why changes in manure can tell us so much about hydration, forage quality, rate of passage and what is happening in the hindgut.
🌱 Seasonal forage changes matter
As the seasons change, so does your horse’s forage base. In many parts of WA, horses may be grazing kikuyu through the warmer months and then need more hay as kikuyu growth slows. In cooler, damper climates with more C3 pasture, the opposite may happen: autumn and winter pasture growth increases, and hay intake may reduce.
Either way, this is not just a simple swap from “grass” to “dry grass”. It changes moisture intake, fibre type, chewing time, salt and water needs, rate of passage, hindgut fermentation and the microbial population in the gut.
Fresh pasture contains far more water than hay. When horses move from pasture to more hay, they often drink more, but they may still produce smaller, firmer, drier or more compact manure. Research in horses moved from pasture to a stabled hay-fed routine found that drinking water intake increased, but total faecal output decreased, faecal dry matter increased and large intestinal motility changed, especially during the first five days of transition (Williams et al., 2015).
A healthy faecal ball should be formed, moist and able to break apart when it hits the ground or when lightly opened. It should not be rock-hard, tight and dry. It should not be liquid. Water should not shoot out before, during or after the faecal balls. Repeated mucus coating over the faecal balls is also not something I would ignore, as mucus may indicate gut irritation, altered transit, inflammation or hindgut disturbance.
The poo you see today may not reflect what the horse ate this morning. Pasture changes may show in the manure within about 24–36 hours, while hay or more fibrous forage changes may take closer to 36–72 hours to fully show. Feed passage varies with forage type, particle size, water intake, movement, gut motility and the individual horse (Cuddeford et al., 1995; Van Weyenberg et al., 2006).
⚠️ Sudden changes matter
This is why sudden feed and forage changes matter. A study on simple colonic obstruction and distension colic found that recent feed or forage change was associated with a much higher colic risk. The risk was highest when changes occurred over 1–7 days, then reduced as the change period became longer (Hillyer et al., 2002).
This does not mean every horse will colic if feed is changed quickly, but it does show why I prefer major forage changes to be made gradually over 14–21 days, and closer to 21 days for horses with previous colic, free faecal water, ulcers, EMS/IR, laminitis history, poor teeth, poor water intake or known hindgut sensitivity. Some horses may need even longer.
It is also important to remember that a horse does not need a new bag of feed or a new bale of hay for the diet to change. Sometimes the “feed change” happens in the paddock.
Sudden weather changes can alter the plant before we change anything. Frosts, cold nights, sunny days, drought stress, sudden rain after dry conditions, or several cold days followed by warm days can all change pasture carbohydrate levels.
Cool-season C3 grasses, such as ryegrass, fescue, cocksfoot, prairie grass and many temperate meadow grasses, can accumulate water-soluble carbohydrates and fructans when photosynthesis continues during the day but growth is limited by cold conditions (Longland & Byrd, 2006; Kagan et al., 2022).
Warm-season C4 grasses, such as kikuyu and Rhodes grass, behave differently. They are not usually “fructan grasses” in the same way many cool-season C3 grasses are. C4 grasses generally store more sugar and starch, with much lower fructan levels than many C3 grasses (Jensen et al., 2014).
However, that does not mean cold-stressed, frosted, drought-stressed or stressed C4 pasture is automatically safe. Cold stress can slow growth, alter dry matter, change palatability and change the amount and type of carbohydrate the horse is eating.
🦠 Hindgut fermentation and fibre
This matters because different carbohydrates are handled differently in the horse. Sugars and starches are generally digested and absorbed earlier in the digestive tract if the amount does not overwhelm the horse’s digestive capacity. Fructans and fibre fractions are fermented by microbes. If too much starch or rapidly fermentable carbohydrate reaches the hindgut, it can favour starch- and sugar-fermenting bacteria, increase acid production, lower pH and reduce the efficiency of fibre-fermenting bacteria (Harlow et al., 2016; Raspa et al., 2022).
This is why high-grain diets, large cereal-based feeds and cereal hay with grain heads can be a problem for some horses. If the hindgut environment is constantly being pushed towards a more acidic, starch-fermenting population, the horse may struggle to use fibre efficiently as its main fuel source. High-starch diets have been shown to alter the equine faecal microbiota and have also been associated with increased behavioural reactivity (Bulmer et al., 2019).
This is also why simply “adding more fibre” does not always fix the problem. The base diet must support fibre fermentation first. That means tested forage, controlled starch and sugar, enough effective fibre, correct minerals, adequate salt and water, movement, dental function and gradual transitions.
Abrupt changes between grass and hay can alter the faecal microbiota of ponies, with changes occurring in the first few days after the diet change (Garber et al., 2020). Research in grazing horses has also shown that moving between warm-season and cool-season grass systems can shift the faecal microbiome, because diet is a key driver of hindgut microbial structure and composition (Weinert-Nelson et al., 2022).
This is especially important for horses in a Mediterranean-type climate like much of south-west WA, where we often move between hot dry summers, dry standing feed, hay feeding, cooler wet winters, sudden autumn breaks, cold nights, warm days and rapid pasture changes.
From the horse’s gut point of view, this can mean big changes in moisture intake, pasture carbohydrate profile, dry matter intake, hay maturity, chewing time, water intake, salt intake, rate of passage and hindgut fermentation.
🌾 Hay quality, fibre and impaction risk
Impaction colic is one of the risks I think about when horses move onto more hay, especially if the hay is mature, stemmy, very dry, dusty, high in NDF, or if the horse is not drinking enough. Fresh pasture brings water into the diet. Hay does not.
For hay, NDF and ADF are very useful. NDF tells us about the cell wall fibre and how bulky or filling the hay is. ADF is linked with maturity and digestibility. As hay becomes more mature and lignified, it may provide bulk, but not always digestible, fermentable fibre. Studies show that forage quality affects voluntary forage intake and digestibility in horses, and lower-quality, more mature forage is generally less digestible (Edouard et al., 2008; Leishman et al., 2024).
For horses prone to impaction colic, free faecal water, EMS/IR, laminitis, ulcers, poor teeth or poor water intake, I would be cautious with hay testing over about 60–65% NDF. I would treat hay around 69% NDF or higher as a major red flag. I would not use very high-NDF hay as the main forage for these horses unless there is no alternative and the diet is being managed very carefully.
The goal is not just to feed “more fibre”. The goal is to feed fibre that the horse can actually chew, hydrate, ferment and pass safely.
🌾 What about straw?
This is where straw needs to be used carefully.
Straw can be useful in small amounts to slow intake and reduce energy intake for some overweight horses, EMS/IR horses and fast eaters, but it is not the same as good-quality hay. Straw is high in structural fibre, low in digestible nutrients and more dependent on hindgut fermentation.
When people quote the research using 50% straw, it is important to understand what that actually means. Jansson et al. (2021) used good hygienic-quality conditioned wheat straw as 50% of the forage ration on a dry-matter basis, in a controlled 2 × 21-day crossover study. The study found longer feeding time, lower energy intake and lower plasma insulin concentrations, without increasing gastric ulcer scores under those study conditions. The wheat straw used in that study was still very high in NDF, testing around 802 g/kg DM (Jansson et al., 2021).
Mostert et al. (2024) used 50% oat straw and 50% haylage in a 2 × 7-day crossover study in eight horses. By Day 7, the consumption rate was significantly lower on the straw and haylage ration, suggesting that oat straw can slow consumption and alter chewing behaviour in a way that may help manage obese horses or horses with low energy requirements (Mostert et al., 2024).
⚠️ That does not mean every horse in WA should suddenly be fed 50% straw.
These studies used controlled, conditioned, hygienic straw and monitored horses. That is very different from feeding poor-quality, dusty, weather-damaged, mouldy, coarse, unconditioned, failed-crop or harvest-waste straw as a major forage source.
Processing, or conditioning straw may help fracture the stem and make it easier for the horse to chew, mix and consume, but it does not turn straw into highly digestible hay. It does not magically remove the high insoluble fibre or lignin. Straw remains a low-energy, low protein high-structural-fibre feed. For WA straw needs to be tested as it can be higher than 10% NSC as fed.
💧🧂 Straw, water and salt
When adding straw, hydration and salt intake become even more important. Straw is much drier than pasture and is high in structural fibre, so the horse needs enough water in the gut to help hydrate, ferment and safely pass that fibre.
Personally, I would not increase straw in a horse that is not drinking well, has dry tight faecal balls, reduced manure output, a history of impaction colic, or is already on very mature or high-NDF hay.
Plain, clean water must always be available. Salt also needs to be managed sensibly because sodium and chloride help support thirst and fluid balance. I would not rely on a salt block/lick alone for horses being managed on drier forage. Measured salt should be introduced gradually into the feed and adjusted for body weight, weather, sweating, workload, forage mineral levels and individual acceptance.
Straw should also be increased slowly. I would usually start at around 5–10% of the forage ration for suitable horses, then hold that level for at least three days before increasing. This does not mean the hindgut microbiome is fully adapted in three days, but it gives time to watch manure output, faecal moisture, appetite, water intake, gas, comfort and early signs of hindgut tolerance.
In sensitive horses, I would hold each step for 5–7 days, or longer.
Any increase should only be made if the horse is drinking well, passing a normal number of manure piles, and the faecal balls remain moist, formed and easy to break apart. If the manure becomes dry, tight, reduced in amount, mucus-coated, or free faecal water appears, I would stop increasing the straw and reassess the whole forage base.
For practical feeding, I would usually be more conservative than the research maximum. For suitable horses, around 10–20% clean, hygienic, chopped or well-processed straw can be a useful tool to slow intake, extend chew time and dilute calories. I would build to that level gradually rather than jumping there suddenly.
I would be very cautious using straw in older horses, dental-compromised horses, colic-prone horses, poor drinkers, horses with dry manure, horses with free faecal water, ulcer-prone horses and horses already eating very mature or high-NDF hay.
Horses are fibre fermenters, but they are not donkeys. Donkeys are the kings of surviving on poor-quality, fibrous forage. Research comparing equids has shown that donkeys can digest straw diets more effectively than ponies, while ponies had the lowest apparent digestibility of straw compared with donkeys and cattle (Pearson et al., 2006).
So, we cannot assume that because a donkey can cope beautifully on very fibrous roughage, that a horse or pony can do the same.
💦 Free faecal water
Free faecal water, occurs when the horse passes formed manure and a separate watery phase. It is not one simple disease with one simple cause. Research describes it as a two-phase faecal presentation, with a solid phase and a liquid phase, and the exact cause is still not fully understood (Lindroth et al., 2022).
In practice, it can be linked with forage type, forage change, hay maturity, water-holding capacity, gut microbial adaptation, starch and sugar load, stress, dental function, parasites, sand, ulcers and individual hindgut sensitivity.
Research looking at forage fibre maturity and fibre source has shown forage type can affect hindgut fluid balance, viscosity and water-holding capacity. Early-cut grass forage may behave differently from more mature grass forage or legume forage in the hindgut (Muhonen et al., 2022; Muhonen & Julliand, 2023).
This may help explain why one hay batch/type can produce lovely manure, while another hay batch/type can produce dry, tight manure, free faecal water, gas or discomfort, even if both bales look “good”.
Prebiotics, probiotics and postbiotics have a place, but they are not magic powders that can override a poor forage base, sudden hay changes, too much straw, poor water intake, high starch intake, or a diet that keeps pushing the hindgut biome towards starch fermentation.
The best-supported area in horses is live yeast, particularly Saccharomyces cerevisiae, where some studies show benefits for fibre digestibility, hindgut fermentation activity and microbial function. However, results are product-specific and diet-specific (Jouany et al., 2009; Boucher et al., 2024).
The aim is not to “kill off” every starch-digesting bacterium. The aim is to stop creating the conditions that favour the wrong population. A fibre-friendly hindgut has a more stable pH and better support for fibrolytic bacteria, the bacteria that help ferment fibre into volatile fatty acids, which the horse can use as an important energy source.
💧🧂 Salt, water and manure
Hydration is just as important as fibre.
Cooler weather does not mean horses automatically drink enough. When the diet becomes drier because hay intake increases, the horse must drink more to replace the water that was coming from fresh pasture.
Salt matters because sodium and chloride help support thirst and fluid balance, but salt needs to be managed sensibly.
Recent research comparing block salt and loose salt found that salt intake varied greatly between individual horses (2g-135g). In that study, 9 out of 16 horses did not meet the estimated sodium requirement based on daily averages, regardless of salt form (Murphy & Catalano, 2025).
This does not mean we suddenly tip large amounts of salt into every feed. Too much salt too quickly can put horses off their feed. Salt should be introduced gradually, measured properly, and adjusted for body weight, workload, sweating, weather, forage mineral levels and individual acceptance.
For some horses, it can help to train them to drink slightly salty water, but plain clean water must always be available as well. Never make salty water the only option.
✅ Practical take-home points
✅ Treat major weather shifts like a feed change.
✅ Change hay, pasture and bucket feeds gradually over 14–21 days.
✅ Use the full 21 days, or longer, for sensitive horses, colic-prone horses, EMS/IR horses, laminitic horses, ulcer-prone horses, older horses, poor-doers, poor drinkers or horses with free faecal water.
✅ Remember, manure changes may lag behind the diet change by one to three days.
✅ Do not change hay type or batch suddenly if the horse is hindgut-sensitive.
✅ Use tested hay before turnout so the horse is not going onto risky pasture hungry.
⚠️ Be careful with frosted pasture, cold-stressed pasture, sunny cold days, drought-stressed pasture and sudden seasonal flushes.
🌾 Use a more digestible, lower-NDF hay where possible for colic-prone or hindgut-sensitive horses.
⚠️ Be cautious with hay over 60–65% NDF.
⚠️ Treat hay around 69% NDF or higher as unsuitable as the main forage for at-risk horses.
🌾 Limit straw, especially in older horses, dental-compromised horses, colic-prone horses, horses with dry manure, and horses that do not drink well.
🌾 For suitable EMS/IR horses and fast eaters, clean chopped straw may be useful at around 10–20% of the forage ration, introduced gradually.
✅ Start straw lower, around 5–10%, then hold each increase for at least three days before increasing again.
✅ For sensitive horses, hold each straw increase for 5–7 days or longer.
💧 Only increase straw if the horse is drinking well, passing normal manure, and the faecal balls remain moist, formed and easy to break apart.
⚠️ Do not assume research using clean, controlled straw applies to poor-quality WA harvest-waste straw.
🧪 Test hay for dry matter, crude protein, NDF, ADF, starch, sugar, minerals and hygienic quality.
💧 Provide clean, plain water and access to salt at all times.
🧂 Introduce measured salt gradually and do not rely on a salt block alone.
🐴 Keep the horse moving where possible, as movement supports gut motility.
💩 Watch the manure daily: number of piles, ball size, moisture, smell, mucus, free water and consistency.
🦠 Support fibre fermentation first with forage, water, salt, minerals and gradual change before relying on gut supplements.
⚠️ Be careful with high-grain feeds and cereal hays with grain heads, especially in EMS/IR, ulcer-prone, laminitic or hindgut-sensitive horses.
⚠️ Hard, tight faecal balls, repeated mucus coating, reduced manure output, liquid manure, free faecal water, or water shooting out around formed manure are all signs to investigate.
🐴 Your horse’s manure is not just waste. It is one of the best daily windows into hydration, forage suitability, fibre fermentation and hindgut health.
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