For starters, more than 70% of the immune system is produced and housed in the gut. And those 'gut feelings'? There’s more to them than we think. The gut and brain are actually connected, and actively communicate with each other. The brain can even impact both the quality of the digestive tract lining, as well as the release of chemicals into the digestive process. It's also the brain that controls the speed at which food moves through the digestive tract. Even certain neurotransmitters, like those associated with mood - think serotonin - are actually produced in the gut.

Poor gut health not only negatively affects digestion, but it can also drive autoimmune diseases, thyroid imbalances, chronic illnesses, and mood disorders like stress and anxiety. Whether human or horse, looking after the digestive system should be an absolute priority, as the overall health of the gut is going to influence everything from behaviour, how the body responds to stress, and even basic survival.

Immune function may also be impacted if we don't get it right, as specialised immune tissue called GALT (Gastric Associated Lymphoid Tissue) is found in the intestines. And no surprise to those regular followers here who know me, one of my favourite subjects - Diet, plays a huge role in gut (and thus brain) health.

No doubt about it - the gut is doing a whole lot of important work that we're probably not even aware of. It's where everything starts. So let’s start at the beginning.

Introduction to gut health

"All dis-ease begins with the gut." So said Hippocrates, who was way ahead of his time because all these centuries later, science proves he was right all along. The digestive system is the Mother of all the body's systems, with the large intestine, aka the hindgut, being the Mother of all the organs. Everything starts with the gut and the integrity of the gut biome, with everything depending on the health of those friendly fibre-fermenting microbe colonies in the hindgut, who produce all the vital metabolites (postbiotics) that fuel both the horse's energy and the body's ability to thrive.

The horse's hindgut region, and specifically the colon, is the deciding point as to whether we have a healthy horse or not. And it's largely governed by the hindgut biome - a diverse ecosystem of microorganisms, including bacteria, viruses, and fungi, to name a few. Yet while many of us associate bacteria with disease, the body is teeming with both beneficial and more questionable bacteria, inside and out, good and bad. We want to nourish the good and eliminate the bad, so that the friendly fermenters continue to process the fibre from the grass forage that their host (our horse) consumes, and keep producing those essentail metabolites.

One of which is a type of fat known as a short-chain fatty-acid, the “short-chain” term describing its chemical structure. These fatty acids are one of several naturally produced postbiotics, and it's these which nourish the cells lining the colon, reducing inflammation, and supporting overall gut health. Fibre literally feeds the good bacteria and encourages their growth, ensuring this production line of nutrient vitality continues.

But it can all go horribly wrong. In a healthy horse's hindgut, the friendly biome colonies coexist peacefully with smaller colonies of less friendly bacteria. However, if that delicate balance is disrupted, a rapid overpopulation of acidic unfriendly microbes can occur, forcing a drop in pH level and leading to a condition known as hindgut acidosis. The bad news? Those vital friendly fermenters can't survive in such high acidity.

And so begins the domino-effect of dysbiosis in the large intestine/hindgut, which if left unattended can lead to SIBO - small intestinal bacterial overgrowth. Hang on. Small intestine, I hear you ask? 'Fraid so. What happens is that some of those unfriendly acidic bugs from the hindgut find their way into the small intestine, which isn't good at all, because the small intestine is meant to be mostly sterile (minus a small amount of beneficial bacteria) and needs to remain that way at a neutral, non-acidic, pH.

If the unfriendlies move in and take over, they'll start fermenting the digesta in the small intestine, i.e. the sugars, starches and proteins. And when fermentation occurs where it's not meant to, it creates inflammation, causing the belly to become bloated. In humans this is what causes IBS.

Worse, if this inflammation in the small intestine becomes pressurised (think of a balloon being pumped up more than it should be), it will rip apart the very fragile intestinal wall. 

Meet leaky gut.

NOTE: Full disclosure - I should add that this lining can also break down from other factors, i.e. stress, antibiotics, or NSAIDs such as bute and steroids, even a relentless low-fibre/high-sugar diet, etc etc. If you've ever had a vet say your horse has a gut yeast overgrowth or infection, as they sometimes like to call it, this is also triggered by these same factors.

The Gut-Brain Connection

Now let's make matters more interesting. The small intestine is also the home of the gut-immune system, which accounts for around 70-80% of the body's total immune system. So, if we've got a leaky gut, we're now in real trouble because harmful substances will now leak into the bloodstream. We're talking about unfriendly pro-inflammatory bacteria, along with particles of putrefactive undigested matter from the small intestine, which once in the bloodstream will start to wreak toxic havoc in the body. This activates an emergency immune response, driving the immune system into a manic, panicked overdrive.

The body is now in a critical toxic state. Cue all kinds of disruptive gut issues, alongside and a tired/wired/foggy brain, and other system-wide problems including allergies, arthritis, autoimmunity, mood disorders, colic, and the dreaded laminitis.

Sound familiar? Welcome to the world of the equine gut system gone wrong.

The importance of the gut microbiome

A healthy gut is the ultimate gatekeeper of good health, and a healthy microbiome the game-changer. It's even been said (in human biome research) that this may well be the decade, or even the century, of the microbiome, with medical science increasingly exploring the interplay between the intestinal biota and the immune system. Those 70-80% immune cells present in the gut need a healthy biome to flourish, which in turn requires different strains of beneficial microbes.

The gut biome is probably the most important regulator of health. There are over 100-trillion gut microbes sending messages throughout the body, interacting with the hormones, the immune system, brain chemistry, and every other system. But when the gut biome's microbes are out of balance, a malfunctioning body is the result - it really is as simple as that. Even in a perfect world, and whether human or horse, the gut has a hard enough time keeping things balanced, because in our modern world there are many things that knock the digestive system off balance.

Here's a thing - our modern-day horse's digestive tract still looks and functions exactly the same as their ancestors' gut systems did from millennia ago. The most common issue, however, is that we've taken our eyes off how and what we should be feeding our horses, and what should - and shouldn't - be passing through their intestinal tract.

And there's a very good reason for this shift. For the last half-century or so, the animal feed industry has capitalised on the growing demand for horse feed, emerging alongside intensive farming practices. And in order to mass produce crops, chemical sprays, i.e. fertilisers, pesticides, fungicides, herbicides, have been utilised by the billion of gallons to improve yields, saturating our soils. To harvest the crop, it's then sprayed with glyphosate to kill it, thus making harvesting quicker and easier. The final cherry on top is a chemical mould inhibitor while the harvested crop is stored in the barn. 

And lest we forget, everything we have eaten for millennia contains the chemical makeup of the soil it grew in or grazed on. A soil biome will have a direct effect on the equine gut biome.

For starters, this means that unless a feed is grown organically, you'll be feeding a product that's been chemically sprayed, and grown in a chemically saturated soil, which our horse then ingests. Additionally, many of today's feeds have strayed from what horses are naturally meant to eat. Instead, some manufacturers have produced feeds that may include cheaper ingredients, without a hint of any grass forage, which can be pro-inflammatory and potentially harmful to the gut. These products are often marketed with shiny healthy images and all kinds of health promises, making it all too easy for us to be swayed by the convenience and attractive packaging.

NB: If you want to find out more, we've got this all covered in depth in our Feeding our Horses Healthy section (main menu bar).

Of course, I could point fingers and name specific companies, but that's not the focus here. Instead, it's up to us to take responsibility and get it right, because as our horses continue to tell us, when we mess with their natural diet, the consequences can be significant. So, let's take a moment to remind ourselves of the basics of equine nutrition and get it right for our horses.

How a horse eats

"Anything that's going on in the digestive tract is influenced by what you put in the digestive tract. You put the wrong fuel in a Ferrari and we know what's going to happen there."
Dr Tom O'Brien, Big Bold Health

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, literally speaking, but the whole gut system, from one end to the other and with all its integral parts in between, has a massive job to do in between. The good news is that our horse knows exactly how it all works, so we need to start taking our lead from them all over again 😏.

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

Let's start where it all starts - the initial rip/tear off the top of a bunch of long grass, followed by the chewing process by the back molars. This mechanically breaks down the forage they've bitten off into tiny pieces of between 2-5mm. Remember right - millimetres. This length is vitally important as the whole digestive process, including peristalsis motility, takes place through a very long - and very thin - tube, aka the small intestine. And successful hindgut fibre digestion, which is where all those vital metabolites/postbiotics are produced, is entirely governed by the length of those chewed, ground-down forage fibres.

Which means ... perhaps we need to take a closer look at chaffs. Chaffs are generally cut into fibre lengths nearing 5cm - that's centimetres. Thing is, this length is too short for a horse to thoroughly chew. Remember the grass lengths a horse naturally rips off with their teeth - we're not talking about short, overgrazed paddocks here. However, 5cm is also too long to be properly digested in the hindgut.

So, when a horse swallows these too-long fibres, it can then alters gut motility (the rate food passes through the small intestine) to slower, because the digesta gets stuck, slowing everything down. This means the fibres can remain festering in the small intestine and/or the colon for several days, leading to a gut-disruptive cascade and various metabolic disorders - an obvious sign is if your horse's droppings are a bit stinky, or smell 'rotten'.

Problem solved

Now, before everyone gets their rulers out, I completely get that it's nigh on impossible to find a chaff made from tiny cut fibres, so my own personal take on this is not to get too anal about it. I personally can't find a chaff that's cut less than 2mm (virtual dust, i.e. mash-like, which I'll never feed unless a horse is sick enough to need help eating again, but that's a whole other subject), or greater than 5cm, and especially one that follows my own personal ethos of organic, diverse, multi-grass species. But - there's also a very simple solution to this, so here's how we solve it.

Don't feed a chaff. Seriously. A horse doesn't need a chaff in the feedbowl, or rather, the feedbowl doesn't need several different allsorts in it. All it needs is a simple grass-forage carrier, i.e. an appropriate 'right-size' cut of meadow grass forage that soaks down, and a Meadow Cob does this perfectly. Think Agrobs, Thunderbrook, and now even Baileys do  one! Job done.

NOTE: Since I originally wrote this in its previous form in our main Nutrition by Condition/Gut System page, in 2022 I then discovered that the Agrobs' Pre-Alpin Senior chaff is cut near as dammit to the perfect length. The annual dental revealed that my Murf (ancient connie) had lost a tooth with his others described as 'worn' So I went hunting, et voila! He's now going to stay on dampened Pre-Alpin Senior chop forever as his feedbowl carrier, to save chew effort and more of the safe swallowing. Happy days.

Back to chaff and ideally, the optimal chaff fibre length is around 8cm minimum, which to the naked human eye is pretty long, but this is the minimum length that will encourage a horse to chew what's in their feed bowl, instead of inhaling it as they usually do. For the record we've heard of dramatic improvements in gut health when clients have sourced a more appropriate chaff length, or ensured adlib hay, with plenty of fibre going through the hindgut, features as the main grass forage.

*Choke Alert - if the food isn't chewed small enough, this can also make horses prone to choking. We know that horses don't generally chew the contents of their feed bucket slowly, so it's all the more important to be aware of the particle sizes, especially if you're also including pieces of carrot or apple. It's really important to make sure they're chopped into tiny pieces - no more big carrot chunks - because if theses aren't chewed thoroughly into little bits, they may get stuck at the bottom of the oesophagus, being too large to pass through the sphincter entrance to the stomach/foregut. Cue choke.

Now to the grinding/chewing ...

In a natural, free-growing landscape of long, stemmy grasses (not what we usually have here in the UK!), the horse will tear off the perfect sized mouthful with their front teeth, then ‘roll’ it into the toothless gap where we 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, this means the job's done, ready for the complex process of digestion. And a reminder - unlike us humans or dogs, horses don't have the luxury of being able to vomit anything nasty back up, so this tasting area allows them to sort out any toxic plant and spit it out to the side, because once it's swallowed, there's no going back.

Once they’re happy with the taste, a horse will roll the forage into a ball - the 'hay roll' - and now here’s where the grinding of the forage takes place, breaking down the grass stem wall and exposing the inner cellulose/hemicellulose fibre that the hindgut microbes break down to produce those vital postbiotics. Grindgrindgrind, until it’s all broken down to 2-5mm pieces, ready to be swallowed. The saliva produced while grinding/chewing adds moisture and mucus to the mix, as well as bicarb which starts to regulate the oesophageal pH level.

Daily trivia - did you know?
To chew 1Kg of hay takes up to 3,500 chewing motions over 40-50 minutes, and generates 3-5 litres of saliva!
(You read that right - an astonishing 3-5 litres!)

Let's just nip back to a reminder of why the fibre length is so important. Remember, if the forage stem isn't ground down to the right size by those back molars, this means that inner cellulose fibre won’t have been exposed. Hence why unchewed fibres will stay in the hindgut for longer (potentially rotting), while the biome microbes try their hardest to get to the inner fibre so they can produce those vital postbiotics.

Back to it, and once the grinding is done, the horse is now ready to swallow and pass the ground 'bolus' into the oesophagus. Now picture a short garden hose, around 1.5-meters long (in an average horse), but only about 1.5cm wide, so you can see how each bolus needs to be finely ground down to pass efficiently. The bolus then finally moves through the lower esophageal sphincter and into the stomach.

Part 1 done! Next up, the art of digestion itself.

Part 2 - Digestion! It's all about the how ...