The Equine Gut Microbiome Explained

Every horse carries one of the most remarkable ecosystems in nature.

Not in its stable. Not on its coat. But inside its digestive tract.

Trillions of microorganisms — including bacteria, fungi, protozoa and archaea — work continuously to digest fibre, produce nutrients and maintain the health of the digestive system. Collectively, these microorganisms form what scientists call the equine gut microbiome.

Although invisible to the naked eye, the gut microbiome has become one of the most important areas of research in equine nutrition. Modern studies increasingly demonstrate that a healthy microbiome is closely linked to digestive efficiency, immune function, nutrient utilisation and long-term performance.

For horse owners, understanding the microbiome is no longer reserved for researchers or veterinarians. It has become an essential part of keeping horses healthy, resilient and capable of performing at their best.

Table of Contents

• What Is the Equine Gut Microbiome?
• The Digestive System: A Perfect Partnership
• Why the Microbiome Matters
• The Hindgut: The Horse's Most Important Fermentation Chamber
• What Influences the Gut Microbiome?
• Signs That the Microbiome May Be Out of Balance
• Supporting the Microbiome Through Nutrition
• Ingredients That Have Received Scientific Attention
• The Connection Between Gut Microbiome and Gastric Health
• Why We Developed VetGen GastroBalance
• Frequently Asked Questions
• Key Takeaways
• References

What Is the Equine Gut Microbiome?

The equine gut microbiome refers to the enormous community of microorganisms living throughout the horse's digestive tract. These include:

• Bacteria
• Archaea
• Fungi
• Protozoa
• Viruses

While bacteria receive most of the attention, every member of this ecosystem plays an important role in maintaining digestive balance.

Unlike humans, horses evolved as grazing herbivores. Their digestive system is specifically adapted to extract energy from plant fibre — a task that horses cannot accomplish on their own. Instead, they rely on their microbiome.

The microorganisms ferment structural carbohydrates found in grasses and hay, converting them into volatile fatty acids (VFAs), which provide a substantial proportion of the horse's daily energy requirements.

Without this microbial fermentation, horses would be unable to efficiently utilise forage as their primary food source.

The Digestive System: A Perfect Partnership

Many horse owners immediately think of the stomach when discussing digestive health. While the stomach is certainly important, it represents only a small part of a much larger and highly specialised digestive system.

The digestive tract consists of:

• Mouth
• Oesophagus
• Stomach
• Small intestine
• Caecum
• Large colon
• Small colon
• Rectum

Each section has a unique function. The stomach begins digestion. The small intestine absorbs proteins, fats and many vitamins. The hindgut — comprising the caecum and large colon — is where the microbiome becomes most active.

This is where billions of microorganisms ferment fibre and produce energy that fuels the horse every day. In many ways, the hindgut functions as a biological fermentation chamber that has evolved over millions of years.

Why the Microbiome Matters

The microbiome does far more than digest forage. Researchers now recognise that it influences numerous physiological processes throughout the horse's body.

Fibre Digestion

Forage is the foundation of every healthy equine diet. However, horses do not possess the enzymes required to digest cellulose. Instead, microorganisms perform this task. During fermentation they produce volatile fatty acids such as:

• Acetate
• Propionate
• Butyrate

These fatty acids provide a significant proportion of the horse's daily energy requirements and support normal digestive function. Without a healthy microbial population, forage utilisation declines dramatically.

Immune Function

Approximately seventy percent of immune cells are associated with the gastrointestinal tract. While the exact percentage may vary depending on methodology, there is little doubt that the digestive tract represents one of the body's largest immune organs.

A balanced microbiome helps regulate immune responses and contributes to maintaining the intestinal barrier. When microbial diversity decreases, digestive disturbances may become more likely.

Nutrient Production

Many microorganisms synthesise nutrients during fermentation. Among them are several B vitamins and vitamin K. Although the horse also receives vitamins from its diet, microbial production contributes to overall nutritional status and demonstrates how closely nutrition and microbiology are connected.

Maintaining the Gut Barrier

The intestinal wall performs two equally important functions. It allows nutrients to pass into the bloodstream while simultaneously preventing undesirable substances from entering circulation.

The microbiome contributes to maintaining this protective barrier by supporting normal intestinal function and producing beneficial fermentation products. Researchers continue to investigate the relationship between microbial diversity and intestinal integrity.

The Hindgut: The Horse's Most Important Fermentation Chamber

The hindgut is often described as the engine of the equine digestive system. It contains an extraordinarily dense and diverse microbial community.

Inside the caecum and large colon, billions of microorganisms continuously ferment fibre from grasses and hay. This process occurs around the clock.

Unlike carnivores, horses are adapted to consume relatively small amounts of forage almost continuously. This steady intake provides the microbiome with a consistent supply of fermentable fibre. Interruptions to this natural feeding behaviour can rapidly influence microbial activity.

What Influences the Gut Microbiome?

The microbiome is remarkably dynamic. Its composition changes constantly in response to nutrition, management and environmental conditions. Some of the most important influencing factors include:

Forage Intake

Forage provides the primary substrate for microbial fermentation. High-quality hay offered throughout the day supports microbial stability far more effectively than long fasting periods.

Dietary Changes

Sudden feed changes can alter microbial populations. Whenever possible, dietary transitions should occur gradually over several days. This allows microbial communities time to adapt.

High-Starch Diets

Large starch meals that escape digestion in the small intestine reach the hindgut. There they can alter fermentation patterns and microbial balance. This is one reason why nutritionists generally recommend dividing concentrate meals into smaller portions.

Stress

Transport. Competition. Hospitalisation. Environmental changes. Even routine management practices may temporarily influence digestive function. While occasional stress is unavoidable, long-term management should aim to minimise unnecessary challenges to digestive health.

Antibiotics

Antibiotics remain essential medications when prescribed appropriately by veterinarians. However, because they may also affect beneficial bacteria, recovery of the microbiome following treatment has become an important area of ongoing research.

Signs That the Microbiome May Be Out of Balance

The microbiome cannot be evaluated simply by observing manure consistency. Instead, digestive health reflects a complex interaction between nutrition, management and microbial populations.

Potential signs that warrant further investigation may include:

• Reduced appetite
• Poor body condition
• Recurrent digestive disturbances
• Loose manure
• Increased gas production
• Reduced performance
• Changes in behaviour
• Difficulty maintaining weight

These signs are non-specific and can have many possible causes. Veterinary examination should always be the first step when digestive disease is suspected.

Supporting the Equine Gut Microbiome Through Nutrition

The microbiome is remarkably resilient — but it is also highly responsive to the horse's daily management. Every meal, every training session and every management decision influences the microbial community living inside the digestive tract.

While no single feed ingredient can "fix" the microbiome, nutritional strategies that respect the horse's natural digestive physiology can help support microbial diversity and digestive stability over time. Research consistently shows that forage availability, feeding management and dietary composition are among the strongest factors shaping the equine gut microbiome.

1. Prioritise Forage

If there is one universal recommendation for supporting gut health, it is this: feed forage first.

Horses evolved to graze for 14–18 hours each day. Continuous access to fibre provides a steady supply of fermentable substrate for hindgut microorganisms while also supporting normal digestive function.

Periods without forage may affect both gastric health and hindgut fermentation. For this reason, many equine nutritionists recommend avoiding unnecessarily long fasting periods whenever possible.

2. Make Dietary Changes Gradually

The gut microbiome does not adapt instantly. Whenever a new feed or forage is introduced, microbial populations require time to adjust.

Sudden dietary changes may alter fermentation patterns and microbial balance, particularly when large amounts of concentrates are introduced. A gradual transition over several days allows the microbial ecosystem to adapt more effectively.

3. Feed Fibre Before Starch

Performance horses often require additional energy. However, energy should not come at the expense of digestive health.

Large starch meals that escape digestion in the small intestine enter the hindgut, where they may alter microbial fermentation and reduce microbial stability. Splitting concentrate meals into smaller portions and maintaining adequate forage intake helps support a more balanced digestive environment.

4. Fresh Water Matters More Than Many Realise

Water is often overlooked when discussing gut health. Adequate hydration supports normal intestinal motility and the movement of digesta throughout the gastrointestinal tract.

Clean, fresh water should always be available, particularly during travel, competition and periods of increased exercise.

Ingredients That Have Received Scientific Attention

Research into equine nutrition has expanded considerably over the past decade. Rather than focusing on "miracle ingredients", modern nutritional science examines how carefully selected ingredients may contribute to maintaining digestive health as part of a balanced diet.

Several ingredients have attracted particular scientific interest.

Pectin

Pectin is a naturally occurring soluble fibre found in many plants. Within the stomach, pectin has been investigated because of its ability to contribute to the physical characteristics of gastric contents and its potential role when combined with other nutritional ingredients.

Pectin is frequently included in premium gastric support formulations because of its compatibility with ingredients that support the stomach's natural protective environment.

Lecithin

Lecithin has also been studied extensively in equine gastric nutrition. Together with pectin, lecithin has been investigated for its potential contribution to maintaining the stomach's natural protective barrier.

Although nutritional support should never replace appropriate veterinary diagnosis or treatment when disease is present, these ingredients have become common components of modern gastric formulations.

Saccharomyces cerevisiae

Among probiotic feed additives, Saccharomyces cerevisiae is one of the most extensively researched in horses. Numerous studies have investigated its influence on fibre digestibility, fermentation efficiency and microbial populations.

While responses may vary depending on diet and management, scientific reviews suggest that yeast supplementation can support cellulolytic bacteria responsible for fibre digestion, particularly in horses receiving higher-energy diets.

Sea Buckthorn

Sea Buckthorn (Hippophae rhamnoides) has become one of the most interesting botanical ingredients in modern equine nutrition. Its berries naturally contain a broad spectrum of bioactive compounds, including carotenoids, flavonoids, polyphenols, vitamin E and essential fatty acids.

Although much of the research has been conducted outside equine medicine, experimental studies have investigated Sea Buckthorn for its potential to support gastrointestinal health through antioxidant activity and by contributing to the maintenance of normal mucosal function. Recent reviews also highlight interactions between Sea Buckthorn polyphenols and the gut microbiota, although further equine-specific research is still needed.

For this reason, Sea Buckthorn has become an increasingly interesting ingredient within premium equine digestive formulations.

The Connection Between the Gut Microbiome and Gastric Health

Horse owners often separate "stomach health" from "gut health." In reality, the digestive system functions as one interconnected system.

The stomach influences what enters the intestine. The small intestine determines nutrient absorption. The hindgut microbiome completes fibre fermentation and supports overall digestive stability.

When nutrition supports only one section of the digestive tract while neglecting the others, long-term digestive function may not be fully optimised. This systems-based understanding has shaped many modern approaches to equine nutrition.

Why We Developed VetGen GastroBalance

At VetGen, we believe that every ingredient should have a purpose.

We did not develop VetGen GastroBalance by selecting the longest ingredient list possible. Instead, we focused on combining carefully chosen ingredients that complement one another within a broader nutritional strategy for gastric and digestive health.

Our philosophy remains simple:

• Science guides every decision.
• Premium ingredients.
• Purposeful formulation.
• No unnecessary complexity.

Rather than chasing trends, we aim to create products built on scientific understanding and practical application for today's performance horses.