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The Gut System

The Mother of all the Systems

Ulcers, a damaged Microbiome (aka SIBO), Leaky Gut or Hindgut Acidosis? Either way, they're all connected - when one area of the gut system has a problem, the rest will as well. And if the fragile, sensitive equine gut function is compromised, the entire body is thrown out of balance.

Principal Body System: Digestive

Definition: A long tube called the gastrointestinal (GI) tract and associated organs, i.e. salivary glands, liver and pancreas.

Function: Performs the physical and chemical breakdown and absorption of food for use by cells, and eliminates solid and other waste.

All dis-ease begins with the gut. So said Hippocrates, who was way ahead of his time, because all these centuries later, there's no doubt about it. The digestive system is the Mother of all the Systems, with the large intestine, aka the 'hindgut', the Mother of all the Organs - everything starts with the gut.

A healthy gut is the ultimate gatekeeper of good health, and a healthy microbiome the game-changer - this may be the decade, or even the century, of the microbiome. The gut microbiome is probably the most important regulator of health; there are 100-trillion gut microbes sending messages throughout the body, interacting with the hormones, the immune system, brain chemistry, and every other system in the body. When the microbiome's microbes are are out of balance, a seriously malfunctioning body is the result. It really is as simple as that.

How a horse eats

- and we need to know this, because if we mess with this, which we do - often, it all goes horribly wrong

The gut system isn't just a tube where food gets shovelled in one end and eventually comes out the other end - well, it kind of is, but the whole gut system, from one end to the other, has a massive job to do in between. The good news is that a horse knows exactly how to do it 😉

First up, it's all about the forage, and trust me - size matters

It all starts with the initial chewing process which mechanically breaks down the forage into tiny pieces of between 2-5mm - this length is vitally important as the whole digestive process, including peristalsis motility, takes place through a very long - and thin - tube, from start to finish, so a successful digestive process is entirely governed by the chewed length of the fibre.

*Choke Alert - if the food isn't chewed small enough, this can make horses prone to choking. We know that horses don't generally chew the contents of their feed bucket slowly - it's more of an inhale 😉 - so we need to take care of the particle sizes, especially with chopped pieces of carrot or apple. Make sure they're chopped into tiny pieces because if they're not chewed properly they can get stuck at the bottom of the oesophagus, too large to pass through the sphincter entrance to the stomach/foregut.

As equally important is not to feed ground or meal forage in too small pieces, as this will speed through digestion, pretty much undigested, a bit like pumpkin or milk-thistle seeds. The optimal forage fibre length is around 8cm minimum - we've heard of dramatic improvements in diet when clients have changed the hay length they feed.

Back to the teeth, and those sharp front teeth do the biting off of the forage, which then goes into that soft area where there are no teeth, where we would normally put the bit. This is a tasting area - horses are very particular about what they eat as once they've committed to chew and then swallow means the job's done, ready for the huge process of digestion. Unlike a dog who will woof anything down regardless (!), and if it's not good it can come back up again. Horses don't have this luxury as they can't vomit, so in this tasting area they can sort out any toxic plant and spit it out to the side. Once it's swallowed, it's a done deal.

If they're happy with what they've bitten off, they roll the forage into a food roll ('bolus') in this middle tasting area, and pass it back between the back molars to do the grinding down before passing into the oesophagus. Think of the oesophagus as a garden hose, around 1.5-meters long in an average horse, but only around a tiny 1.5-cm wide, so all the food has to pass through this long and very narrow tube.

This grinding also exposes all the inner forage fibres that the hindgut microbes will then break down into the horse's energy. Chewing also creates saliva which adds moisture and mucus to the mix, as well as starting to regulate the pH level. Some interesting stats for you - to chew 1kg of hay takes up to 3,500 chewing motions over 40-50 minutes, and generates 3-5 litres of saliva!

Digestion - it's all about how it's digested

The chewed food now passes into the foregut to be broken down into a soupy mix (called 'chyme'), to then pass into the small intestine for the microbiome to separate out the essential nutrients so they can be absorbed into the bloodstream to fuel the body, before shuttling off the remaining fibre to the hindgut for fermentation and energy production in the colon, with the resulting waste made up of 50% waste lignan fibre/50% micro-organisms, shifting on to the main elimination exit point and coming out in perfect parcels of poo 😉

And it doesn't do all this by itself - the very function of the gut system relies entirely upon it's own army of elements. The horse's digestion operates via enzymatic digestion in the stomach, aka ‘foregut’, with most (over 50%) of the protein pre-digestion and most soluble carbohydrate pre-digestion; fats are broken down in the small intestine by bile, ahead of the large intestine, or ‘hindgut’, which is where we'll find the cecum and two colons, and this is where it's all about bacterial, aka microbial fermentation, of the fibre sources such as grass and hay. And because our horses' energy comes from the fibre digestion, keeping the microbiome, aka friendly bacteria/flora/biota, well-populated in the hindgut is right up there at the top of the list of priorities.

Horses normally consume 2-2.5% of their body weight in dry fibre matter each day, although if they’re on pasture 24/7 this can go up to over 3%. Remarkably, the capacity of the stomach of the horse is small, about the size of a rugby ball and coming in at just 8 to 15-litres depending on the horse-size. So, it begs the question as to how a horse can consume such large amounts of food/water when constantly grazing. Easy - the time it takes for food to transit from the stomach to the small intestine is anywhere between 2-6hrs, and it never empties; as the horse continues to eat, the digesta trickles through into the small intestine, hence the term ‘trickle feeders’. The rate of passage through the small intestine is about 1ft/minute, with the average length in total of the small intestine being around a whopping 70-feet.

The foregut

The foregut is the only part of the gut system that's acidic, in order to both kill off contamination and also to activate the protein digestive enzyme - the acid is there for a reason, and without it the rest of the gut function is in trouble. Once digesta moves into the small intestine and onwards, the gut needs a neutral pH - it's a huge problem if any part of the rest of the digestive system becomes acidic.

The foregut as where the pre-digesting of the foodstuff happens, and it does it via 3-sections. The first section, the pars nonglandularis, has a reasonably high pH, between 5-6, so not too acidic - there's no stomach acid in the front section of the foregut, but what we do have here is resident lactic acid bacteria, usually brought in by the horse ingesting it from their feed/forage. STOP PRESS!! Under normal circumstances the last thing we want in the gut system is lactic acid bacteria, and certainly not in the hindgut (!) but in this front section of the stomach it's normal, and the good news is that they have a useful job to do as well. More on this throughout this chapter.

These lactic acid bacteria make lactic acid from eating starch and sugar in the feed - it's where they derive their energy from as they can't utilise plant fibres. So, when the horse has ingested starches, the lactic acid bacteria start pre-digesting the starch molecules which makes them easier for the small intestine to digest further on. Clever little bacteria 😉

Now to the middle section, and this is where the pepsinase enzyme, the protein digester, is produced. This then needs to be activated into pepsin which performs the protein pre-digesting. This activation can only happen when the stomach pH drops to below 4, when the digesta hits the hydrochloric acid in the back section of the stomach.

The back section, pars glandularis, is where the hydrochloric acid sits, where it basically disinfects any nasties in the feed such as microbial contamination (it's how dogs survive eating other dogs' poop, as well as other revolting rotting foodstuffs, with their acid pH value a super-severe 1!), as well as (mentioned earlier) activating the protein digestive enzyme, pepsinase, into pepsin, to start to degrade the proteins in the feed. Horses have a hydrochloric acid pH of around 3 - less harsh than a dog or cat - which reduces the level of microbial contamination in the feed, but not 100%.

In summary, a normal foregut process is that a horse should have a constant uptake of roughage so that the stomach remains full, with a pre-digestion of starch via lactic acid bacteria in the first section with production of lactic acid, pepsinase production in the middle section, and the back section covering activation of pepsinase to pepsin, alongside inactivation of any remaining lactic acid bacteria and microbial decontamination on the feed. Once done, the pre-digested starches and proteins are now ready to exit the stomach into the small intestine.

The rest of the journey

Once the digesta hits the small intestine, bile is released to digest the fats, while the small intestine's biota assimilate the nutrients ready for absorption. Finally we get to the hindgut, where the fibre is fermented down by the hindgut's own microbiota, and this is where the horse gets their energy from. And all the while there have been fluids and mucus to lubricate and keep everything moving along the way as well.

Without these essential elements, the gut system won't be able to do the very job it's meant to do, which is to keep the body alive. Without them it won't be able to digest the food or supplements that we pay good money to keep our horses healthy. If digestion is impaired, so will begin a cascade of seriously chronic dis-ease.

This life-dependent function relies entirely on maintaining a healthy inner-gut environment, and the only way to do this is by feeding foods that boost the good bugs and weed out the bad bugs - this is critical for maintaining a healthy inner environment and preventing leaky gut syndrome, which these days is now rampant.

So, if you're looking to clear up the chronic symptoms that are chipping away at your horse's quality of life, there's only way to do it - feed a constant supply of quality, high-fibre, grass roughage. We need to look after our horse's gut health first and foremost, as the top priority. And ... this applies as much to humans as horses too, although obviously we're not going to start eating hay 😉

NB. The foal and growing horse have undeveloped cecal and colonic digestion compared to the adult horse. There is very little microbial digestion before 3 months of age, so the foal requires a diet low in fibre and one that is easily digested in the foregut. Foals who are seen eating their mothers' droppings are thought to be obtaining a bacterial culture necessary for future microbial digestion, so if you see it happening, encourage it!

Now to the flora - the all-important Microbiome, the body's 2nd Brain

Collectively the beneficial and pathogenic microbes outnumber the regular cells in the whole, entire body, by an astonishing 10-1 - at least (!). Think about that for a second - there are a whopping 10-times more bugs in the gut system, that long tube from mouth to the final exit point, than in the entire rest of the physical body. Which means if the microbiome gets disrupted, we're in a whole lot of trouble. So, looking after our horse's gut microbiome by feeding it what it needs - course, stemmy, cellulose-rich fibrous hay - is crucial, as amongst it's many vital roles, it's also the first line of defence against many serious diseases.

For starters, without a healthy microbiome, there's no nutrient absorption, which as we know is crucial to fuel a healthy body. But it's so much bigger than this - the microbiome literally runs the show. Over 70% of our horse's immune cells are created by the gut microbes in the intestinal tract and this microbiota is also the major regulator of the immune system - the difference between healthy and unhealthy relies entirely upon the gut microbiome's performance.

Unfortunately, there are also certain medical treatments which can really mess with the gut ecology, such as antibiotics, bute and chemical wormers, which disrupt the relationship in a similar way that chemotherapy affects the human body. Chemotherapy wipes out perfectly healthy non-cancerous cells inside the human body along with the cancerous cells, annihilating the immune system. Similarly, antibiotics completely wipe out the gut bacteria, the bad bugs as well as the good bugs the body can’t live without.

A healthy gut system is absolutely essential for overall health and vitality - sounds obvious I know but an effective digestive process means your horse will absorb the nutrients you spend a fortunte on trying to get into them. Again, it's a much bigger picture though; a healthy gut will also significantly minimise the laminitis/colic risk, and protect the horse against infections such as diarrhoea-causing organisms like salmonella or clostridium.

The good news is that a healthy, functioning digestive system is really straightforward to manage - it really is, provided we feed them the right stuff, as in the food that their gut is meant to eat. Because ... the equine digestive system is also extremely sensitive, and it doesn't take much to upset the delicate gut ecology and environment; poor diet/dietary management, obviously, but chronic stress can equally play an enormous part in affecting gut health. Poor gut health can manifest itself in so many ways, from the obvious signs of loose droppings, lack of overall vitality, allergies or pain.

For the full story on how critical a part the microbiome plays in overall health, see our separate chapter below, The Microbiome - the Missing Organ? I promise you it's an eye-opening read ...

Leaky gut syndrome - introducing 'dysbiosis' and SIBO

“Dysbiosis (also called dysbacteriosis) is a term for a microbial imbalance or maladaptation on or inside the body, such as an impaired microbiota.” Wiki

The lining of the gut's small intestine is supposed to be strong and tight, keeping food, microbes and waste safely inside the digestive tract. So why is 'leaky gut syndrome' now becoming a new epidemic?

As above, I can't stress enough how important it is to centre our attention on the microbiome, and specifically those beneficial gut microbes, to avoid dysbiosis. Another fact - it's the microbiome, as in a healthy one, filled with lots of happy, beneficial microbes busying away down there sorting out the nutrients and fermenting the fibre in the hindgut , that regulates the permeability, aka leakiness, of the gut wall lining - this is the connecting factor.

When the gut bacteria balance is disrupted and the balance between the friendly microbes and pro-inflammatory toxic bad microbes reverses, those bad microbes set up camp and create inflammation, This is known as SIBO - Small Intestinal Bacterial Overgrowth, and SIBO isn't funny. For starters, the inflammation then disrupts the tight junctions of the gut wall which makes it permeable, as in leaky, and allows the undigested, seriously toxic waste in the small intestine to leak through the gut and into the bloodstream, literally poisoning it. This triggers an almighty inflammatory autoimmune cascade as the immune system goes into hyper-overdrive, trying to fight those leaked toxins.

Cue the battlefield. Special antibodies, aka immunoglobulins, live in the horse's gut to protect the body. The immunoglobulins IgA and IgM help identify the toxins, and begin the attack by calling in the regiments of killer-army white blood cells. And the more overwhelming the leaked toxin burden is, the longer the battle, and the greater the inflammation, not to mention red-hot pain.

Be under no illusion - leaky gut affects the whole process for just about every medical condition, be it joint, skin, brain - hooves especially as leaky gut causes laminitis. Everything depends on the integrity of that gut wall membrane, which astonishingly is a mere 1-cell thick, so you can appreciate just how vulnerable the gut lining is.

Vaccines don't help either, as vaccines can contain proteins and other food particulates. This is because manufacturers use cells from animals, like chicken embryo and bovine serum, to grow the antigen. When the antigen finishes growing, they separate it from the protein, but sometimes small amounts can end up in the vaccine. During vaccination, these food proteins and other components get introduced into the body.

Cue yet another exaggerated immune response. All these components are identified as enemies, and when any enemy shows its ugly face, it’s time for battle.

These days we have the knowledge and the tools to get the diet right - forage/roughage fibre all the way - which nurtures the microbiota to flourish, in order to maintain its production of the important nutrients - which include producing the B-vits, vit.C and several amino acids - that body needs to benefit health. This is a whole separate chapter in itself - see our Feeding our Horses section, and specifically the Why what we feed has to be right page.

For the full story on leaky gut, see our separate chapter below - Leaky Gut - a Growing Epidemic. For the latest updates on SIBO, see our Blog Post - SIBO – another case of ‘everything’s connected’

Faecal water/Diarrhoea

Any metabolic gut disturbances, i.e. diarrhoea/faecal water/excess gas, are all signs of dysbiosis in the hindgut. Certainly a chemical wormer is going to have wreaked havoc with the biome and gut membrane integrity overall, not to mention liver function, so there could very well also be something leaky going on as well.

Coarse stemmy hay is going to be your saviour here – absolutely not haylage as this creates lactic acid in the hindgut, nor grass as this is too leafy, with not enough fibre and full of pectins which also create lactic acid in the hindgut. With a horse being solely a hindgut fibre fermenter, we need to get those all-important roughage plant fibres, cellulose and hemicellulose, found in stemmy hay, back into the hindgut to rebalance the biome, so try not to go for an early or 2nd hay cut as this will have been cut from grass blades only which are high in pectins – we need a late-only cut where the grass has flourished enough to seed, so there’s lots of stem full of cellulose.

Also, many essential nutrients are produced by the hindgut biome, including the B-vits and many amino acids, so there there’s every chance that there’s now a B-vit and amino-acid deficiency. Feeding hay will help get things back on track but it might be worth giving a B-vit and Essential Amino Acids supplement for a while until the hindgut’s happier again. We have both these supplements available in our Individual Items/Nutrients shop page.


- when we refer to ulcers, we're talking foregut ulcers. Hindgut 'ulcers' is a completely different thing; for starters they don't exist - they're a myth - because there are no acid-secreting cells in the hindgut. There is, however, Hindgut Acidosis, caused by lactic acid in the hindgut. If you've been told your horse has 'hindgut ulcers', see our separate Hindgut Acidosis chapter (link also at the bottom of this page).

Here’s a thing – foregut ulcers are there because the gut environment has been already altered, usually due to either some form of stress, inappropriate feed, or stress caused by inappropriate feed. These factors are the cause of why our horses – and us humans – get ulcers. Stress and/or the wrong food/food management destroy the gut environment, literally, which means that without a strong, healthy protective mucosal gut lining, the stomach acid will leak and create a wound, aka an ulcer, because it’s almighty strong hydrochloric acid, same as a car battery.

Sounds simple enough doesn’t it. Yet most of us have no idea how many vital roles the stomach acid plays in the body, whether horse or human, and ... the drug companies know it too. You can’t watch TV without seeing an advert for some chalky tablet to ‘calm’ the acid burn, especially after we've eaten a red hot curry.

The claim that the acid is causing the ulcers is a myth. The acid splash/leak is merely a side-effect of the stress/poor diet which has caused the damage in the gut.

  • Remove the stressors
  • Refocus on your training/discipline - considerate short bursts to allow your horse to process what you're trying to communicate
  • Switch feed to species-appropriate (see Why what we feed has to be right in our Feeding our Horses section)
  • Avoid any sweet feeds (Musli's/Beet) - it's what the pro-inflammatory gut microbes gorge on. which causes them to multiply and kill off the beneficial microbes that do all the good stuff like digestion
  • Avoid haylage (high lactic acid %)
  • Steam hay, don't soak it - soaking increases the bacterial content of hay
  • Make sure there’s continuous ad-lib forage
  • Let a horse be a horse, allowed to express their natural behaviour with freedom, buddies and social interaction - as the saying goes, 'Friends, Forage, Freedom'.

This isn't complicated - it's straightforward horsecare. Sadly we inherit a lot of damage when we take on a new horse so there's often a lot of unravelling and unpicking to do, but if you remind yourself that a horse is a horse (and not a cow, human or robot), and factor horse needs into your care, you'll very likely witness a remarkably quick, not to mention a safe and natural recovery, without having to shovel damaging symptom-blocking chemicals (Proton Pump Inhibitors, aka PPIs) which have horrible side-effects, into our horses' already altered - and damaged - digestive systems.

There's a useful YouTube video to check if you think your horse is ulcerogenic - see the bottom of the page for the link. Meanwhile, see our dedicated Ulcers page, link also below, for the full story on PPIs.

Probiotics and Prebiotics

Despite the similarity in their names, probiotics and prebiotics are not different forms of the same - they each have unique mechanisms of action on the gut.

  • Probiotics are a supplement added into the diet to promote the colonisation of the beneficial microbes, usually recommended to be added to the diet after gut illness such as faecal water syndrome/colic/diarrhoea, or after a gut-damaging course of antibiotics or a chemical wormer.
  • Prebiotics are a natural food source that feed those beneficial microbes, stimulating the microbiome's growth and activity - we don't need to add any supplement advertised as a prebiotic because the best source is - you've guessed it - cellulose, from coarse, stemmy, cellulose-rich hay, preferably made from a diverse range of meadow grasses. if you look at products sold specifically as ‘prebiotics’, i.e. inulin, you’ll see they’re based on pectins, which we definitely want to avoid as pectins create lactic acid in the hindgut and lower the pH value, turning the hindgut environment acidic.

It's exactly the same in the human world - plant/vegetable fibre is our finest prebiotic to feed our own gut flora, so eat your greens, chop up an onion and grate yourself a carrot 😉

The latest science (Spring 2021) is now saying that we don't need to feed a probiotic all the time, only when the gut's been disrupted as mentioned above. There's also the fact that all the available products on the market aren't appropriate for the fragile equine gut ecology - currently there’s no probiotic available that mimics the microbiome of the horse. It's also not so much about what type of microorganism – it’s about diversity. Remember, the whole microbiome - the very eco system of all the trillions of bacteria bugs in the gut system - outnumber the body’s cells by 10-1; they outnumber DNA cells by 100-1, so the current thinking is now saying that adding in one type of microbe is barely going to touch the sides.

Back to our horses and which probiotic? Personally I feed Alltech's probiotic Yea-Sacc 1026, a live yeast culture based on the Saccharomyces cerevisiae strain. If ever there was dire digestive compromise such as salmonella/e.coli, or risk of, I'd add Alltech's BioMos as it specifically binds to bad bacteria and eliminates them.

If you need to feed a probiotic, we sell Yea-Sacc either separately in our Individual Items section so you can add independently to the feedbowl, or in our EquiVita 'ProB' range of mineral balancers where we include the 10g RDA.

General pointers for a healthy gut system

  • Horses are herbivores which evolution has designed to graze on a diverse range of high fibrous, low-energy forages up to at least 20 hours per day - in the perfect world this forage should consist of multiple diverse grasses, plants, barks etc., to create a diverse microbiome.
  • Here In the UK the best feed your horse can put in his mouth is hay, grass in its dried form. The bulk delivered by a fibrous hay diet is a key weapon in avoiding colic because consistent gut-fill maintains a continuous level of digestive activity. Additionally, the more horses chew, the more saliva is generated and mixed in with the mouthful of hay, which helps buffer the GI tract against excess acidity.
  • Unfortunately, domesticated living usually challenges the horse's sensitive digestive tract with inappropriate processed feedstuffs, irregular feeding schedules and ration portions that are far outside the norm of the natural plan. One of the primary reasons that horses colic is the difference between what the digestive system is meant to process and what it actually gets.
  • Make changes in feed slowly over a period of a few days and be careful about overfeeding manufactured processed feeds prior to an event.
  • Keep your horse moving – stabled horses are much more prone to gut issues than those who live out. Turnout with companions keeps horses happy, allows them social interaction and lets them eat their favourite food. Not only is the horse free to consume the ideal fibrous diet, but the simple, continual act of moving to eat, enhances motility of keeping the food moving along in the gut.

Top Tips

  • To promote healing of the gut, this is where the right kind of bacteria comes into play. The right kind of bacteria will break down fibre in the diet into molecules that are really easily used by the gut cells as energy sources. So other than making sure our horse has plenty of fibre and the right kind of bacteria in the gut to heal the gut, there are two essential amino acids you can use, especially if you're dealing with gastric ulcers or leaky gut. N-Acetyl L-Cysteine (NAC), the precursor to glutathione (arguably the most powerful antioxidant in the body) replenishes glutathione production. Glutamine is a building block for proteins that maintain cellular health and tissue repair. During critical illness, trauma, intestinal disease, excessive loss of lean body mass, and extreme endurance exercise, Glutamine is shown to be beneficial. Glutamine also works in synergy with NAC to help promote glutathione. We've blended both these amino acids together as a gut support in our GutAminos blend.
  • Aloe vera juice is a beneficial gut supporter. It's high in digestible fibre which gives it the properties of lowering bowel transit time, supporting hindgut bacteria and soothing the digestive tract overall. Aloe also contains a complex mixture of mucopolysaccharides (complex sugars) that nourish cells and support them in replicating. Aloe juice is also especially important for gut acid; its polysaccharides can be helpful for horses who have been on buffering agents that destroy the healthy bacterial populations in the gut and thus allow pathogenic bacteria to multiply. Good quality aloe juice can be found in most health food stores - add 50-100ml to feed when your horse is displaying symptoms.
  • Slippery Elm v Marshmallow Slippery Elm is a renowned gut-healing herb with similar properties to Aloe. However, the native populations of the slippery elm tree are suffering due to its worldwide popularity and the tree is now considered extremely rare; as a result it's now a protected species which is reflected in its price - slippery elm isn't cheap! The good news is that marshmallow herb can be suitably substituted for slippery elm because marshmallow has almost identical properties and is so much more widely available - and cheaper too! Of course we supply both. Marshmallow root has a higher mucilage % than the leaf so is the better one to go for for gut soothing, with the leaf more indicated for respiratory tract soothing. Add 50ml Aloe and 1-desertspoon of marshmallow to feed.
  • Aloe and Marshmallow are not only beneficial for digestion in general but also support excess gut acidity as well. They can both be fed long term with no negative effects.
  • Apple Cider Vinegar is also invaluable for gut health - not only is it a beneficial supporter of immunity, it's also rich in natural probiotics, beneficial enzymes and acids that help absorption of nutrients.

"How to diagnose equine ulcers" - Mark DePaolo, DVM

Just 5-mins long, and shows the varying foregut ulcer symptoms in 3-horses – mild symptoms, then moderate, finishing with a horse with severe symptoms.

NB - ignore the recommended Omeprazole/PPI route at the end, and head to our dedicated Ulcers page below which explains the risks of PPIs!