In Part 1, we explored how crucial a healthy gut is for overall well-being, highlighting its connection to the immune system, brain function, and behaviour. We delved into the horse's natural eating habits and the role of the hindgut biome in producing vital nutrients (postbiotics).

Now, let's move to the next stage and examine the fascinating process of digestion, where the gut transforms food into essential energy and nutrients for our horses. And it all starts with the stomach, aka the foregut. We look at how food is broken down with the help of stomach acid and digestive enzymes. We also discuss the crucial role of the small intestine in nutrient absorption and the importance of maintaining a healthy hindgut biome.

By understanding and supporting this complex system, we can drastically improve our horse's health and well-being.

The stomach/foregut

We left Part 1 with our horse’s back molars having ground down the mouthful of forage, with the now chewed food 'bolus' swallowed, passed through the lower oesophageal sphincter, and into the stomach.

Remember that saliva from the chewing process? This has already activated the stomach’s digestive ‘juices,’ so specific digestive enzymes are now on standby to begin the protein and starch pre-digestion process. The stomach’s muscle wall now starts agitating like a washing machine, churning and liquefying the bolus before it gets 'disinfected' by the stomach acid and turned into a soupy mix called chyme. This chyme will then pass easily into the small intestine (SI).

But let’s stay with the stomach acid for a moment. The foregut is the only part of the whole gut system that's meant to be acidic. Once digesta moves into the small intestine and onwards, the gut environment should sit at a neutral pH for the rest of the journey. Yet many of us have seen the symptoms when the intestines become acidic, which sadly is all too common these days.

Why stomach acid is important

Stomach acid serves two really important functions:

• Converting pepsinase into pepsin: This is all about protein digestion. The stomach acid converts the protein digestive enzyme, pepsinase, into pepsin, without which proteins won't get digested. And on a serious note - if undigested proteins get into the hindgut, this will cause serious problems for the horse.
• Killing off contamination: Stomach acidity is the body's first defence against harmful bacteria, so here’s a stomach ulcers thing. If we suppress the production of acid with PPIs - proton pump inhibitors, aka any of the ulcer pharma drugs ending in 'zole', we let harmful pathogens in through an open door into the intestines, which will have a profound effect on both the gut biome and hindgut function. Without this vital acid, we risk (a) contaminants entering the small intestine and (b) impaired protein digestion.

The Three Sections of the Stomach

The stomach pre-digests food via three anatomical sections:

• Pars Nonglandularis: This section has a reasonably high pH (between 5-6) and contains no stomach acid. Instead, it houses resident lactic-acid bacteria (LA), usually ingested by our horse from feed/forage. Under normal circumstances, the last thing we want anywhere near the intestines is LA bacteria, but in this front section of the stomach, they actually have a useful job, producing lactic acid from eating starch and sugar in the feed, making starch molecules easier for the small intestine to digest further on.
• Middle Section: This is where the pepsinase enzyme (protein digester) is produced. This then needs to be activated into pepsin to perform 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.
• Pars glandularis is where the hydrochloric acid sits, to disinfect any contaminants in the broken-down digesta. This is how dogs survive eating other dogs' poop and other revolting rotting foodstuffs (if anyone has a labrador you’ll understand … 😲), as their acid pH value is a super-severe 1. The equine stomach acid has an acid pH of around 3, less harsh than a dog or cat, reducing microbial contamination in the feed but not eliminating it entirely. PS - this is also the region where the horse experiences glandular, aka pyloric ulcers, caused by stress resulting in poor blood flow which is then unable to produce the protective mucus layer on the mucosa membrane.

In summary, here's the normal foregut process

• Starch pre-digestion occurs via LA bacteria in the first section, producing lactic acid.
• Pepsinase, the precursor to pepsin, the protein digester, is produced in the middle section.
• Acid in the back section converts pepsinase to pepsin to begin protein pre-digestion, while disinfecting any remaining LA bacteria and microbial contaminants in the food.
• Once pre-digestion is complete, the chyme (pre-digested starches and proteins, along with fibre matter) is now ready to exit the stomach and move into the small intestine.
• And to keep this all working as it should, a horse should always have a constant uptake of grass forage to keep the stomach full, active, and operating.

Digestion! The small intestine

Now the hard work starts! Proteins, starches, carbs, and fats (EFAs, i.e., Omega-3 from grasses) are fully digested in the small intestine. This is where micronutrients (vitamins, minerals, amino acids, etc.) are assimilated and absorbed into the bloodstream to nourish and/or repair the body. What remains – forage fibre/roughage - continues on to the large intestine (the hindgut), where the fibre-fermenting microbes get to work on the fibre to produce essential postbiotics which keep our horse thriving, i.e. activated B6, B12, amino acids, and the all-important short-chain fatty acids (SCFAs) responsible for the horse's energy production. The leftovers - 50/50 fibre/microorganisms - eventually exit as perfect poo parcels. 😉

Horses normally consume 2-2.5% of their body weight in dry fibre matter each day, although this can exceed 3% if they’re on grass pasture 24/7. Remarkably, the capacity of the horse's stomach is small, about the size of a rugby ball, 8-15 liters depending on the horse's size. So, how can a horse consume such large amounts of food/water when constantly grazing?

Here’s how:

• The time for food to transit from the stomach to the small intestine is between 2-6 hours.
• As the horse continues to eat, the digesta continues to trickle into the small intestine, hence the term ‘trickle feeders.’
• The rate of passage through the small intestine is about 1-ft/minute, with the total length of the small intestine being around a whopping 70 feet.
• Meanwhile, fluids and mucus keep everything lubricated and moving along the way as well.

The rest of the journey - the hindgut

Finally! We’ve reached the hindgut – the Mother of all the organs, where the vital fibre fermentation by the hindgut's friendly biome begins. If this process is impaired, a cascade of chronic disease can start. Wild horses manage their gut systems naturally, but domestic horses rely on us to maintain their gut health, to prevent hindgut acidosis/dysbiosis/SIBO, which if left untreated can lead to leaky gut syndrome, which is so prevalent these days that it’s now considered an epidemic. See our Blog Post on The Misery of SIBO for more details.

Note: Foals have undeveloped colonic digestion compared to adult horses, with minimal microbial digestion before 3-months of age, so during this time foals require a low-fibre diet that’s easily digested in the stomach while they’re building their hindgut biome. Foals seen eating their mothers' droppings (coprophagia) are attempting to obtain a healthy bacterial culture for future microbial digestion. Encourage this behaviour! See our Creating the Foal's Microbiome page.

A quick digress to the all-important microbiome

Due to the obsessively sanitary nature of modern existence, bacteria tend to have a bad reputation! However, the microbes in the gut biome play an immense role in helping digest food and sorting nutrients for absorption. They regulate the immune system, improve mood, stabilise weight, and remove environmental toxins. Focusing on improving gut health by nurturing the friendly bacteria is key to achieving optimal physical and mental health because gut health IS health.

Collectively, the beneficial friendly and unfriendly microbes outnumber the regular cells in the whole body by an astonishing 10:1 (at least!). Think about that for a second - that's at least 10 times more bugs in the intestinal tract than in the rest of the body. Which means - if the microbiome is disrupted, the whole body’s disrupted. The gut biome is the body's CPU - it literally runs the show. The difference between healthy and unhealthy relies entirely upon the gut biome's performance.

So what Disrupts the Biome?

Plenty, unfortunately. Certain medical protocols can really mess with the gut ecology, such as antibiotics, bute, PPIs, and chemical wormers. They disrupt the relationship similarly to how chemotherapy affects the human body, which wipes out healthy non-cancerous cells along with cancerous cells, significantly compromising the immune system. Similarly, antibiotics wipe out the gut bacteria, the bad as well as the friendlies the body relies on. Activated charcoal has the same effect because it doesn't discriminate between good and bad bacteria. It's great for stomach pumping in an A&E emergency, but not so great for selective bacterial removal.

A healthy gut biome also significantly minimises the risk of laminitis and colic, and protects the horse against infections such as diarrhea-causing organisms like salmonella or clostridium.

No question - the horse’s gut microbiome is the cornerstone of health, influencing systems far beyond digestion alone. By understanding and supporting this complex system, horse owners can drastically improve their horse’s quality of life and prevent a host of health issues.

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

Prioritise gut health

Lest we forget, the equine digestive system is extremely sensitive, so it doesn't take much to upset the delicate gut ecology and environment. Obviously poor diet/dietary management, i.e. letting our horse run out of forage, is a given, and chronic stress can equally affect gut health. Poor gut health can manifest itself in so many ways, from loose droppings and pain to allergies and lack of overall vitality.

It's a no-brainer that we should always prioritise our horse's gut health, right at the top of the list. And the good news is that maintaining a healthy, functioning digestive system is really straightforward, so long as we feed our horses what they’re meant to eat.

Coming up in Part 3

You’ve probably heard about prebiotics and probiotics, and we’ve already touched on postbiotics. That’s a lot of “biotics,” I know – and it can be confusing. In Part 3, we’ll walk you through how they’re different, why each one matters, and the most effective ways to give your horse’s gut the nutrition it deserves.