Fibre in the Equine Diet: Foundation of Good Nutrition

Why Fibre Is the Most Important Part of Your Horse's Diet

If there is one golden rule of feeding horses, it's this: fibre comes first. Before you think about concentrates, balancers, supplements, or anything else, your horse's diet must be built on a solid foundation of fibre.

This isn't just a nice idea — it's rooted in the biology of the horse. The equine digestive system evolved over millions of years to process a near-constant supply of fibrous plant material. When we get fibre right, everything else in the diet tends to fall into place. When we get it wrong, problems follow.

In this article, we'll explore exactly why fibre is so critical, how the horse's gut processes it, how much fibre your horse actually needs, and the best sources to include in your feeding plan.

How the Horse's Digestive System Is Designed for Fibre

To understand why fibre is so important, you need to understand a little about how your horse's gut works.

Horses are hindgut fermenters. Unlike cattle, which ferment fibre in a large rumen at the front of the digestive tract, horses do most of their fibre fermentation in the caecum and large colon — a vast chamber system that makes up roughly 60% of the total gut volume.

Inside the hindgut, billions of microorganisms — bacteria, protozoa, and fungi — break down the structural carbohydrates in fibre (cellulose, hemicellulose, and pectin) through fermentation. This process produces volatile fatty acids (VFAs), which are absorbed through the gut wall and used by the horse as a major source of energy.

In fact, for most horses at rest or in light work, VFAs from fibre fermentation can supply 60–70% of their total energy needs. That's an extraordinary amount of fuel coming from something as simple as grass and hay.

The Trickle-Feeding Principle

In the wild, horses spend 16–18 hours a day grazing. Their stomachs are relatively small, designed to handle a slow, continuous flow of food rather than large, infrequent meals. The horse's stomach continuously secretes acid — whether there is food present or not.

Fibre plays a critical role here. As the horse chews fibrous forage, it produces saliva, which is naturally alkaline. This saliva helps to buffer the stomach acid and protect the sensitive upper portion of the stomach lining. When a horse goes for extended periods without fibre, that acid has nothing to buffer against, and the risk of gastric ulcers increases dramatically.

This is why forage should never be restricted for long periods, and why fibre access is just as much about when your horse eats as what it eats.

The Health Benefits of Adequate Fibre

Getting fibre right doesn't just keep the digestive system ticking over — it has far-reaching effects across your horse's entire health.

1. Digestive Health and Gut Motility

Fibre provides the bulk that keeps food moving through the digestive tract at the right pace. Without enough fibre, gut motility slows, and the risk of impaction colic rises. The physical structure of long-stem fibre is particularly important — it creates a fibrous mat in the gut that promotes healthy, consistent movement.

2. A Healthy Hindgut Microbiome

The microbial population in the hindgut depends on a steady supply of fibre to thrive. When the diet is high in fibre and low in starch, these populations remain stable and balanced. Sudden changes — especially an increase in starch or sugar — can cause rapid shifts in microbial populations, producing excess lactic acid, lowering the pH in the hindgut, and potentially leading to hindgut acidosis, laminitis, or loose droppings.

A fibre-first diet supports a diverse, stable microbiome, which in turn supports the immune system and overall wellbeing.

3. Hydration and Electrolyte Balance

Fibre, particularly in the form of forage, acts as a water reservoir in the hindgut. As fibre is fermented, it holds significant amounts of water and electrolytes, which the horse can draw upon during exercise or in hot weather. A horse fed adequate forage before exercise has a meaningful internal water reserve — one reason why forage access before competition is so important.

4. Mental Health and Behavioural Wellbeing

Horses are hard-wired to chew. A horse that has free access to forage spends a large portion of its day engaged in a natural, satisfying behaviour. Restricting fibre can lead to stereotypic behaviours such as crib-biting, weaving, and wood-chewing — all signs of frustration and unmet behavioural needs.

Providing adequate fibre isn't just about nutrition. It's about allowing your horse to express normal behaviour, which is fundamental to good welfare.

5. Weight Management

This may seem counterintuitive, but fibre is actually an excellent tool for managing weight in both directions. For horses that need to gain condition, high-quality, calorie-dense fibre sources such as alfalfa or unmolassed sugar beet can add calories without the risks associated with high-starch feeds. For good doers that need to lose weight, lower-calorie fibre sources like late-cut hay or soaked hay can keep the gut full and the horse satisfied while reducing overall energy intake.

How Much Fibre Does Your Horse Need?

As a general rule, your horse should consume a minimum of 1.5% of its bodyweight in forage dry matter per day. For a 500 kg horse, that's at least 7.5 kg of dry matter from forage daily.

Many nutritionists recommend aiming for 2% of bodyweight when possible, which would be 10 kg of dry matter for the same horse. Remember that fresh grass and haylage contain significant moisture, so you'll need to feed a greater weight of these forages to achieve the same dry matter intake compared to hay.

Here's a rough guide:

These are estimates — the actual dry matter content of your forage will vary. This is one reason why having your forage analysed is so valuable. If you're unsure whether your horse's diet is meeting its fibre requirements, analysing your horse's diet with a tool like MyEquiBalance can help you identify gaps and make informed adjustments.

Can You Feed Too Much Fibre?

For the vast majority of horses, it's very difficult to overfeed fibre, provided you're managing total calorie intake. The main exception is the overweight horse or the horse prone to laminitis on lush, high-sugar pasture — but even here, the solution is to choose the right type of fibre, not to cut it out.

Best Sources of Fibre for Horses

Not all fibre is created equal. Here are the most common fibre sources available to horse owners, along with their strengths.

Hay

Good-quality meadow or timothy hay is the cornerstone of most horse diets. It's widely available, relatively easy to store, and provides long-stem fibre that promotes chewing and saliva production. Ideally, have your hay tested to understand its sugar, protein, and mineral content.

Haylage

Haylage is grass that has been cut, wilted, and baled at a higher moisture content than hay, then sealed to ferment. It tends to be more digestible and can be lower in dust, making it a good option for horses with respiratory issues. However, it's typically higher in energy and can spoil quickly once opened.

Grass

Fresh pasture is the most natural fibre source for horses. However, grass quality and sugar content vary enormously throughout the year, and managing grass intake is crucial for laminitis-prone or overweight horses.

Alfalfa (Lucerne)

Alfalfa is a legume that provides higher protein and calcium levels than grass hay. It's an excellent fibre source for horses in hard work, breeding mares, and young growing horses. It can also be a useful addition for horses prone to gastric ulcers, as its calcium content and protein help buffer stomach acid.

Unmolassed Sugar Beet

Sugar beet pulp is a highly digestible fibre source that is very palatable and easy to chew, making it ideal for older horses or those with dental problems. It must be soaked before feeding. Choose unmolassed varieties to keep sugar content low.

Fibre-Based Chaffs and Short-Chop Feeds

Chopped fibre products — often a mix of straw, alfalfa, and dried grass — can be useful for adding fibre to a meal, slowing eating speed, and acting as a carrier for supplements. They should complement, not replace, long-stem forage.

Straw

Feeding straw (particularly oat or barley straw) in controlled amounts can be useful for good doers as a low-calorie fibre source. However, straw is low in nutritional value and, if overeaten, can increase the risk of impaction. It's best used as part of a mixed forage approach rather than as the sole fibre source.

Common Mistakes with Fibre in the Horse's Diet

Even well-meaning horse owners sometimes get fibre wrong. Here are the most frequent pitfalls:

• Restricting forage too severely for overweight horses. Dropping below 1.5% of bodyweight in forage dry matter can compromise gut health and increase stress. Use lower-calorie forage, slow feeders, or soaking instead.
• Over-relying on concentrates. A horse in moderate work can often meet its energy needs from quality forage plus a balancer. Grain-heavy diets displace fibre and can destabilise the hindgut.
• Ignoring forage quality. Mouldy, dusty, or very mature hay is not just unpalatable — it can cause respiratory disease, colic, or nutritional deficiencies. Invest in the best forage you can source.
• Leaving horses without forage overnight. Extended periods without fibre (more than 4–5 hours) increase the risk of gastric ulcers. Use slow feeder nets or multiple small haynets to extend eating time.
• Not accounting for forage in the overall diet. Forage provides energy, protein, and minerals — sometimes in significant quantities. Failing to account for this can lead to over- or under-supplementation.

Building a Fibre-First Feeding Plan

The simplest and most effective approach to feeding any horse is to start with forage and work outwards:

1. Choose a quality forage that suits your horse's needs — hay, haylage, or managed grass.
2. Feed at least 1.5–2% of bodyweight in forage dry matter daily.
3. Have your forage analysed so you know what nutrients it provides and where the gaps are.
4. Fill nutritional gaps with a suitable balancer or supplement, rather than adding concentrates by default.
5. Only add additional energy sources (such as oil or fibre-based conditioning feeds) if your horse's workload genuinely demands it.

This approach respects the horse's digestive design, supports gut health, and minimises the risk of diet-related problems such as colic, ulcers, laminitis, and behavioural issues.

Final Thoughts

Fibre isn't just one part of the equine diet — it is the diet, or at least it should be. Everything else we feed is supplementary to the forage foundation. When fibre intake is adequate and appropriate, the horse's digestive system functions as nature intended, and many common health and behavioural problems simply don't arise.

Before you reach for another scoop of hard feed, ask yourself: is my horse getting enough fibre? Is the forage quality good? Do I know what nutrients my forage is actually providing?

If you're not sure, that's the place to start. Get the fibre right, and you'll have built the strongest possible foundation for your horse's health and performance.