Digestion of Forage by Horses

Digestion of Forage by Horses

By Dr Duncan Houston

A horse’s digestive system is built for one job above all others: processing forage steadily over many hours. That matters because many of the most common equine problems, including colic, gastric ulcers, hindgut upset, and founder, begin when feeding no longer matches that design. Horses are not built for long fasting periods, large grain meals, or low-fiber routines. They are built to graze.

This is why forage management matters so much. When owners understand how the equine gut handles fiber, and how badly it handles overload and interruption, feeding decisions become much clearer. The goal is not to feed like a textbook ideal. It is to feed in a way that works with the horse’s actual digestive anatomy.

Quick Answer

Horses are hindgut fermenters, which means they digest forage fiber mainly in the cecum and large colon rather than in a rumen like cattle. This system works best when horses receive steady access to forage and minimal large starch meals. Feeding in a more natural, forage-first way helps reduce the risk of colic, gastric ulcers, hindgut upset, and founder.

Horses Are Hindgut Fermenters

This is the key concept.

Unlike cattle, horses do not ferment forage at the start of the digestive tract. They ferment it later, in the hindgut, especially in the cecum and large colon. That means the horse depends heavily on microbial fermentation after feed has already passed through the stomach and small intestine.

In practical terms, horses:

• digest protein, fat, and simple carbohydrates in the small intestine

• ferment fiber later in the cecum and large colon

• rely on steady forage flow to keep this system stable

This is why horses can do very well on forage-based diets, but can run into trouble quickly when the feeding pattern becomes too concentrated, too infrequent, or too starch-heavy.

Why This Matters for Everyday Feeding

A horse’s gut is not just designed to handle forage. It is designed to handle forage often.

That means:

• small amounts over many hours

• frequent chewing and saliva production

• continuous fiber movement through the digestive tract

• steady microbial fermentation in the hindgut

When feeding no longer looks like that, risk rises.

The most common consequences include:

• gastric ulcers from long fasting periods

• colic from gut disruption or poor motility

• hindgut acidosis from excess starch overflow

• founder in susceptible horses when diet becomes metabolically unsafe

Decision checkpoint

If a horse spends long hours without hay or pasture, the digestive system is already being pushed away from how it was designed to function.

Why Horses Are Not Like Cows

Owners sometimes assume all herbivores handle forage in roughly the same way. They do not.

Cattle ferment feed in the rumen before it reaches the main enzymatic digestive phase. Horses do the opposite. Their fermentation chamber is late in the process, not early.

That difference matters because:

• horses are less tolerant of large starch overload reaching the hindgut

• fiber still matters enormously, but is handled differently

• feeding mistakes can destabilize the hindgut faster than many owners realize

A horse can live on forage beautifully. It just needs that forage delivered in a way the equine gut expects.

The Stomach Is Small and Always Producing Acid

The horse’s stomach is relatively small, and acid production continues even when the horse is not eating.

That is one reason horses are vulnerable to gastric ulcers when:

• forage is limited

• meals are infrequent

• stabling reduces grazing time

• travel or competition disrupts routine

Forage helps because it:

• keeps material in the stomach

• increases saliva production

• buffers acid more effectively than long empty periods

This is why feeding once or twice a day with long gaps in between does not suit equine digestive physiology, even if it looks convenient from a management point of view.

The Small Intestine Handles Only So Much

The small intestine is where the horse digests:

• protein

• fat

• simple sugars and starch, within limits

• many vitamins and minerals

But there is a limit to how much starch this part of the gut can process efficiently in one meal.

If too much starch is fed at once, some of it escapes digestion and moves into the hindgut. That is where problems can begin.

What Happens When Starch Reaches the Hindgut

When excess starch reaches the cecum and large colon:

• it ferments rapidly

• pH drops

• beneficial fiber-digesting microbes are disrupted

• inflammatory byproducts and toxins may be released

This can contribute to:

• gas and colic

• manure changes

• endotoxemia

• laminitis or founder

• systemic inflammation

This is one of the clearest reasons why large grain meals do not fit equine digestive design.

Decision checkpoint

If a horse needs concentrate, the question is not only what feed is used. It is also how much is fed at one time, and whether the small intestine can realistically handle it.

Why Modern Management Often Creates Problems

Many common management systems work against the horse’s digestive biology.

Typical problems include:

• long hours stalled without enough forage

• one or two larger meals per day

• heavy reliance on concentrates

• mature, stemmy, inconsistent hay

• limited turnout and movement

These patterns may be normal in domestic horse keeping, but they are not normal for the horse’s gut. That mismatch is where many digestive disorders begin.

Why Forage-First Feeding Works Better

Forage-first feeding supports the horse’s digestive system by:

• keeping fiber moving through the gut

• increasing chewing time

• increasing saliva production

• reducing acid exposure in an empty stomach

• supporting healthier hindgut fermentation

• lowering the chance of starch overload

This does not mean every horse should live on hay alone. It means forage should remain the nutritional foundation, and everything else should be built around it carefully.

Better Forage Strategies

A more horse-appropriate feeding system usually includes:

Feed forage as the main part of the ration

Hay and pasture should usually form the core of the diet.

Reduce long fasting periods

Use slow feeders, more frequent hay feeding, or turnout to keep intake steadier.

Minimize unnecessary starch

Do not use grain as the default answer unless the horse genuinely needs it.

Maximize turnout and movement

Movement supports gut motility and allows more natural feeding behavior.

Keep the diet consistent

Frequent abrupt changes in forage or concentrate can destabilize the hindgut quickly.

Choose Forage Wisely

Not all hay is equally useful.

Better forage often tends to be:

• leafy rather than overly stemmy

• harvested at a more digestible stage

• clean and free of mold or dust

• appropriate for the horse’s metabolic and calorie needs

For some horses, especially those with laminitis risk, Equine Metabolic Syndrome, or insulin dysregulation, forage testing becomes especially important.

What matters most is not whether the hay looks premium. It is whether it suits the horse in front of you.

How Worried Should You Be?

Low risk

• horse has steady forage access

• concentrate feeding is limited and sensible

• manure, appetite, and comfort are stable

Action: Maintain the current structure and review periodically.

Moderate risk

• longer gaps without forage

• moderate grain feeding

• variable hay quality

• mild digestive sensitivity

Action: Review feeding frequency and forage consistency.

High risk

• large grain meals

• prolonged fasting periods

• history of ulcers, colic, or founder

• obvious mismatch between diet and digestive needs

Action: The ration structure needs a more careful rethink.

Critical risk

• active laminitis or founder

• recurrent colic

• significant manure changes

• clear ulcer suspicion

• rapid worsening after diet change

Action: Veterinary assessment and a stricter diet plan are needed promptly.

Common Feeding Mistakes

Feeding too few times per day

This increases fasting time and gut instability.

Relying too heavily on grain

This increases the risk of starch overflow into the hindgut.

Ignoring forage quality

Poor-quality hay can reduce intake, digestibility, and gut stability.

Assuming pasture is always safe

Grass can still be too rich for some horses.

Feeding for convenience instead of digestive design

Convenience feeding often clashes with how the horse actually processes food.

Practical Feeding Checklist

When Is This an Emergency?

The feeding structure itself is not the emergency. The horse can be.

Seek veterinary advice urgently if your horse develops:

• signs of colic

• sudden foot soreness or founder signs

• severe appetite change

• major manure changes

• dullness after a feed-related change

• suspected gastric ulcer pain with worsening condition

At that point, this is no longer just a nutrition discussion. It is a medical issue.

FAQs

What does it mean that horses are hindgut fermenters?

It means they ferment fiber mainly in the cecum and large colon, which are toward the end of the digestive tract.

Why are big grain meals risky?

Because the small intestine may not digest all the starch, allowing excess to reach the hindgut and disrupt fermentation.

Why does forage help prevent ulcers?

It increases chewing, saliva production, and stomach buffering, while reducing long empty periods.

Are horses designed to eat all day?

They are designed to eat small amounts of forage for many hours a day, not to fast for long periods between meals.

Can poor feeding structure contribute to founder?

Yes. In susceptible horses, excess sugar or starch intake and digestive disruption can be major triggers.

Final Thoughts

If you want to prevent digestive disease in horses, start by feeding for the animal the horse actually is. Horses are not built for long fasting periods, large concentrate meals, or heavily interrupted forage intake. They are built for slow, steady, fiber-based feeding.

That is why forage-first management remains the gold standard. The closer your feeding program comes to supporting natural grazing behavior, the more stable the horse’s digestive system usually becomes. And when the gut stays more stable, the risks of colic, ulcers, hindgut upset, and founder fall with it.

If you want help building a forage-first feeding plan for colic prevention, ulcer risk, or founder-prone horses, ASK A VET™ can help you work through the next step clearly.