The Horse's Gut – How It Really Works (1/5)

Your horse eats well, moves around, seems healthy – yet sometimes something isn't quite right. Hindgut-related diarrhea, restlessness, colic susceptibility, coat problems. Symptoms that at first glance seem to have little in common. On closer inspection, almost all of these issues point to the same place: the gut.
The equine gut is one of the most fascinating and at the same time most sensitive systems in the animal world. It is longer than a school bus, processes up to 15 kilograms of roughage daily – and reacts to the smallest changes. Anyone who understands how this digestive tract truly works will understand their horse on a whole new level.
This article is the foundational piece in our series "Gut & Detoxification in Horses". No prior knowledge necessary – just curiosity.

A digestive system that wasn't planned this way – yet works perfectly.
The horse is a steppe animal. Evolutionarily, it is designed to graze 16 to 18 hours daily – small amounts, continuously, primarily fibrous grass. The stomach is tiny in relation to body size: only 10 to 15 liters capacity. For comparison: a cow has a rumen with 100 to 200 liters.
This means: the horse is not made for large meals. It is designed for continuous, small amounts of feed.
In modern housing systems, this often looks different – concentrated feed twice a day, several hours without roughage, little movement. No wonder the gut gets out of balance.

The Journey Through the Equine Gut – Station by Station

1. The Mouth and Pharynx: Where It All Begins

Even before food reaches the stomach, digestion begins in the mouth. Horses chew intensely – with good hay, up to 3,000 chewing movements per hour. During this process, the food is mixed with saliva, which contains important buffering agents. This saliva neutralizes stomach acid. The more the horse chews, the better buffered its stomach is.
What this means: Little roughage = little chewing = little saliva = more stomach acid. Gastric ulcers often arise not from too much acid, but from too little buffering.

2. The Stomach: Small but Mighty

The horse's stomach continuously produces acid – even when empty. This makes evolutionary sense: in nature, it is never empty. In modern keeping, it often is.
It has two areas: the non-glandular upper part (without mucosal protection) and the glandular lower part. Food residues that remain in an empty stomach for too long can irritate the unprotected upper mucosa – this is one of the main causes of gastric ulcers in horses.
Zeolite connection: Zeolite can adsorb excess acid and irritants in the stomach and soothe the mucous membranes – especially during periods of stress or change.

3. Small Intestine: The Fast Lane

From the stomach, the chyme enters the small intestine, which is about 20 to 25 meters long. Here, water-soluble nutrients are absorbed: protein, fats, simple carbohydrates, many vitamins, and minerals.
The small intestine works quickly – its contents pass through in less than an hour. This is important to understand: too much starch at once (e.g., a large portion of concentrated feed) overwhelms the small intestine's capacity. What is not absorbed moves on to the large intestine – and starch should ideally not reach there.

4. The Large Intestine: The Heart of Equine Nutrition

This is where the amazing things happen. The horse's large intestine – consisting of the cecum, large colon, and rectum – holds 100 to 130 liters and harbors a huge community of microorganisms: bacteria, fungi, protozoa. Together, they form the microbiome.
These microorganisms ferment the indigestible crude fiber from hay and grasses into short-chain fatty acids – the horse's main energy source. The horse meets up to 70% of its energy needs this way.
The microbiome is not a constant, but a balance. And this balance is surprisingly fragile.

Impressive Figures: The Equine Gut at a Glance

• • Total length of the digestive tract: approx. 30 meters
  • Stomach volume: 10–15 liters (only 8% of total volume)
  • Large intestine volume: 100–130 liters
  • Daily feed intake: 10–15 kg hay
  • Daily saliva production: 30–40 liters
  • Microorganisms in the large intestine: Several billion per milliliter of intestinal content
  • Transit time in the large intestine: 36–72 hours

The Microbiome – The Underestimated World in the Equine Gut

When we talk about gut health in horses, we are primarily talking about the microbiome. This community of trillions of microorganisms is not only responsible for digestion. It influences the immune system, mood, metabolism – and susceptibility to diseases.
A healthy microbiome is diverse and balanced. Certain bacterial groups keep others in check. Beneficial bacteria produce substances that strengthen the gut wall and inhibit inflammation.

What disturbs this balance?

• • Abrupt feed changes (especially during spring grazing)
  • Large amounts of concentrated feed that introduce undigested starch into the large intestine
  • Antibiotic treatments
  • Stress (transport, competition stress, stable changes)
  • Poor hay quality with mycotoxins
  • Lack of exercise
  • Long periods without food

The result: dysbiosis – a shift in the balance towards unfavorable bacterial groups. And dysbiosis is the starting point for many of the complaints that horse owners face daily: hindgut-related diarrhea, colic susceptibility, immunodeficiency, coat problems.

Why Horses Are So Much More Sensitive Than Other Animals

This is anatomically explained. Unlike ruminants, horses do not have a rumen that acts as a buffer. Fermentation only occurs in the large intestine – after the stomach. This means:

• • Feeding errors directly and quickly affect the most sensitive part of the digestive tract
  • The transition from fiber-rich to starch-rich diets is particularly risky
  • Horses cannot vomit – whatever goes wrong in the stomach or gut must pass through the gut
  • Changes in the microbiome can quickly lead to life-threatening colic

This is not a design flaw. It is the evolutionary response to a niche: grazing steppe animals that continuously consume small amounts of simple food. The problem arises when we take them out of this niche.

The Gut-Brain Axis in Horses – More Than a Gut Feeling

Recent research shows: the gut and brain constantly communicate with each other – via the vagus nerve, via hormones, via neurotransmitters that the microbiome itself produces. In humans, this is called the gut-brain axis. In horses, this connection is at least as pronounced.
This explains why gut problems are often accompanied by behavioral abnormalities: restlessness, sensitivity, poor trainability. And it explains why stress – a reaction of the nervous system – directly impacts the gut.
A horse that is internally restless often also has a gut that is out of balance. And vice versa.

What Zeolite Has to Do With It

Zeolite is a natural volcanic mineral with a unique lattice structure. This structure allows the mineral to act like a sponge – it can bind and transport pollutants, excess acids, mycotoxins, and fermentation gases out of the gut.
But zeolite does even more: it has an anti-inflammatory effect on the intestinal mucosa, supports the stabilization of the microbiome, and can improve stool consistency – especially in horses prone to hindgut-related diarrhea.
So it doesn't target a single symptom, but the system – the balance of the gut.
In part 4 of this series, we will examine the study situation in more detail. Today, it's enough to know: the gut needs a stable environment. And zeolite can help protect this environment.

Frequently Asked Questions

★ Why is the equine gut so much more sensitive than that of a dog or cow?

Horses are monogastric hindgut fermenters – meaning fermentation occurs only in the large intestine, after the stomach, without a buffering rumen before it. Therefore, feeding errors have direct and rapid effects.

★ What is the microbiome and why is it so important?

•        Part 1: The Horse's Gut – How It Really Works ← you are here

•        Part 2: Signs Your Horse Has Gut Problems – 12 Warning Signs

•        Part 3: Mycotoxins in the Equine Gut – The Silent Risk in Hay

•        Part 4: Zeolite and the Equine Gut – What Animal Research and Practice Jointly Confirm

•        Part 5: Gut Cleanse for Horses – Step-by-Step Program with Zeolite

 

Read more:

Zeolite – Everything You Need to Know About Feeding It to Horses: Q&A and Guide
Feeding Zeolite to Horses – Dosage, Application & Practical Tips