How Horses Digest Forage and Why Forage-First Feeding Matters

By Dr Duncan Houston

Horses are not small cows with nicer manes.

They are herbivores, but they digest forage very differently from cattle, sheep, and goats. Cows ferment feed in the rumen before it reaches the main digestive tract. Horses are hindgut fermenters, which means most fibre fermentation happens later, mainly in the cecum and large colon. Ohio State University describes horses as non-ruminant, simple-stomached herbivores whose large intestine is the main site of fermentation for fibrous feedstuffs. (CFAES)

This matters because the horse’s digestive system works best with a steady flow of forage. When modern management replaces grazing with long fasting periods, large grain meals, sudden feed changes, or low-fibre rations, the risks increase: ulcers, colic, hindgut upset, loose manure, behavioural stress, and laminitis in vulnerable horses.

Quick Answer

Horses digest forage mainly through microbial fermentation in the hindgut, especially the cecum and large colon. Those microbes break down fibre from hay and pasture into volatile fatty acids, which the horse can use for energy. Because the system depends on steady fibre intake, horses do best on a forage-first diet with frequent access to hay or pasture, limited large grain meals, gradual feed changes, and clean water at all times.

How Is a Horse’s Gut Different From a Cow’s?

Cows are ruminants. They have a rumen, which is a large fermentation chamber before the true stomach. Feed is fermented early, then partially regurgitated and rechewed as cud.

Horses do not have a rumen. They have a single stomach, a small intestine, then a large hindgut made up of the cecum, large colon, small colon, and rectum. Fibre fermentation happens after the stomach and small intestine, mainly in the cecum and colon. Iowa State University Extension describes hindgut digestion in the horse as primarily microbial, involving bacteria, protozoa, and fungi that break down dietary fibre. (Iowa State University Extension)

That design has strengths and weaknesses.

The strength is speed. Horses can graze for many hours, pass feed through the foregut relatively quickly, and extract energy from fibre through hindgut fermentation.

The weakness is sensitivity. If too much starch reaches the hindgut, if feed changes happen too quickly, or if forage intake stops for long periods, the microbial balance can be disrupted.

What Does the Cecum Do?

The cecum is a large fermentation vat on the right side of the abdomen. It is not just a storage pouch. It is one of the most important fibre-processing areas in the horse.

The microbes in the cecum and colon ferment plant fibre and produce volatile fatty acids, often shortened to VFAs. These VFAs are absorbed and used as a major energy source.

The cecum and large colon help the horse get energy from:

• Hay

• Pasture

• Grass fibre

• Legume fibre

• Beet pulp

• Other digestible fibre sources

The real clinical point is this: your horse is not mainly designed to be powered by large cereal grain meals. They are designed to be powered by steady fibre fermentation.

Why Forage Is the Foundation of the Diet

Forage is not filler. It is the base of normal equine digestion.

Forage supports:

• Normal chewing

• Saliva production

• Gastric buffering

• Gut motility

• Hindgut microbial balance

• Manure consistency

• Behavioural wellbeing

• Reduced boredom

• Reduced fasting time

• More natural feeding patterns

MSD Veterinary Manual states that most healthy horses should have free access to forage, salt, and fresh water, and many horses on good-quality forage require little or no concentrate supplementation. It also warns that high-starch or high-sugar concentrate making up more than 50 percent of ration dry matter increases the risk of laminitis, colic, and equine gastric ulcer syndrome. (MSD Veterinary Manual)

In practice, the mistake I see most often is treating hay as the background diet and the bucket feed as the “real feed.” For most horses, it is the other way around.

How Much Forage Does a Horse Need?

A common baseline is to feed at least 1.5 percent of body weight per day as forage dry matter, with many horses doing well closer to 2 percent depending on body condition, workload, forage quality, and metabolic risk.

For a 500 kg horse, that means roughly:

Hay is not 100 percent dry matter, so the actual weighed amount may need to be slightly higher depending on moisture content.

Underweight horses, horses in work, lactating mares, and some seniors may need more. Overweight horses, ponies, donkeys, and laminitis-prone horses may need restricted calories, but restriction should still be done carefully so the gut is not left empty for long periods.

Why Feeding Frequency Matters

Horses evolved to graze for many hours each day, taking in small amounts of forage almost continuously.

Modern management often does the opposite: two large meals, long gaps without forage, limited turnout, and large concentrate feeds. That creates a mismatch between biology and routine.

Long gaps without forage can increase gastric ulcer risk. A review of equine fibre requirements reports that more than six hours without access to forage has been found to significantly increase the risk of gastric ulcers in stabled horses. (PMC)

The practical rule is simple:

A horse’s gut is usually safer with many small fibre intakes than with long fasting periods followed by large meals.

Why Large Grain Meals Can Cause Trouble

Grain and starch are not evil. Some performance horses need additional energy. The problem is dose, meal size, horse type, and gut tolerance.

Starch from cereal grains such as oats, corn, and barley is meant to be digested mainly in the small intestine. If too much starch escapes small-intestinal digestion and reaches the hindgut, it can disrupt the microbial population and increase acid production. That can contribute to hindgut acidosis, loose manure, colic risk, behavioural changes, and laminitis risk in susceptible horses.

MSD Veterinary Manual recommends that horses should not receive more than 0.5 percent of body weight in grain-based concentrate in a single meal. For a 500 kg horse, that is no more than 2.5 kg in one meal, and many horses need far less than that. (MSD Veterinary Manual)

For easy keepers, seniors, horses with EMS, PPID, previous laminitis, ulcers, or recurrent colic, the safest approach is usually forage-first, low-NSC, and calorie-controlled.

Severity Guide: How Risky Is Your Feeding Routine?

The real concern is not one imperfect feed day. It is the repeated pattern of low forage, high starch, long fasting, and sudden changes.

What Else Can Go Wrong When Forage Is Poorly Managed?

Several common equine problems are linked to feeding patterns.

Gastric ulcers

Horses produce stomach acid continuously. Forage chewing produces saliva, which helps buffer acid. Long fasting periods reduce that natural buffering.

Impaction colic

Low water intake, poor forage quality, reduced movement, and dry fibre can contribute to impaction risk. MSD Veterinary Manual notes that inadequate water access can decrease feed intake and increase the incidence of impaction colic, anhidrosis, equine gastric ulcer syndrome, and other disorders. (Merck Veterinary Manual)

Hindgut dysbiosis

Sudden diet changes, too much starch, antibiotic use, stress, and low fibre intake can alter the hindgut microbial population.

Laminitis risk

In insulin-dysregulated horses, high non-structural carbohydrate intake from grain or pasture can worsen insulin responses. These horses often need controlled pasture access and low-NSC forage.

Behaviour problems

Horses without enough forage time may show boredom, wood chewing, cribbing, weaving, aggression at feeding, or anxiety around meal times. Not every behaviour problem is nutritional, but the feeding routine often plays a role.

When Is This an Emergency?

A feeding issue becomes urgent when your horse shows signs of colic, laminitis, choke, severe digestive upset, or grain overload.

Call your vet immediately if your horse has:

• Pawing, rolling, flank watching, or repeated lying down

• No manure or very reduced manure

• Severe diarrhea

• Refusal to eat

• Signs of choke, such as coughing feed or saliva from the nostrils

• Sweating, depression, or weakness

• Heat in the feet

• Strong digital pulses

• Reluctance to walk

• A pottery or “walking on eggshells” gait

• A rocked-back laminitis stance

• A known grain binge

• Sudden abdominal bloating

• Signs of dehydration

Do not wait to see if a grain overload or suspected laminitis “settles overnight.” Those are time-sensitive situations.

What Should You Do Right Now?

1. Look at forage first

Before changing supplements or bucket feeds, ask:

• How much hay or pasture does the horse actually get?

• How many hours per day is forage available?

• Is the hay clean, palatable, and appropriate?

• Does the horse finish it quickly and then stand empty?

• Is another horse preventing access?

• Is the horse losing or gaining weight on the current forage?

The feed room is usually less important than the hay stack.

2. Reduce long gaps without forage

Aim to avoid long fasting periods where possible.

Useful strategies include:

• More frequent hay feeding

• Slow feeder nets

• Multiple hay piles for groups

• Hay stations around a track system

• Smaller, more frequent meals

• Turnout where safe and appropriate

Slow feeders should be used sensibly. They should not be so restrictive that the horse becomes frustrated, damages teeth, or cannot meet forage needs.

3. Keep grain meals small

If concentrates are needed, split them into smaller meals.

For many horses, the better sequence is:

1. Forage first

2. Then concentrate if needed

3. Then monitor manure, appetite, body condition, and energy

Do not use grain to compensate for poor hay without fixing the forage problem.

4. Make feed changes gradually

Hindgut microbes need time to adapt.

Change hay, pasture, grain, fat, beet pulp, balancers, and supplements gradually over 7 to 14 days where possible. Higher-risk horses may need even slower transitions.

Sudden changes are one of the simplest ways to upset an otherwise stable gut.

5. Match forage to the horse

Not every horse needs the richest hay.

A hard keeper in work may need higher-quality hay, alfalfa mix, or added calories. An overweight pony with previous laminitis may need tested low-NSC hay, controlled intake, and restricted pasture.

The right forage depends on:

• Body condition

• Workload

• Age

• Dental health

• Metabolic risk

• Ulcer history

• Colic history

• Pasture access

• Manure quality

6. Provide clean water and salt

Forage digestion depends on hydration.

Make sure water is always available, clean, unfrozen, and easy to access. Provide salt daily or free choice as advised. Water intake often drops in cold weather, which can increase impaction risk.

7. Watch the manure

Manure is a useful daily gut-health report.

Monitor:

• Number of piles

• Moisture

• Shape

• Odour

• Undigested fibre

• Sand

• Loose manure

• Free fecal water

• Reduced output

A change from your horse’s normal pattern matters more than a textbook ideal.

Common Mistakes Owners Make

Treating grain as the main feed

For most horses, forage should be the foundation. Grain is a tool, not the base diet.

Leaving horses without hay for long periods

Long fasting periods increase ulcer risk and do not match equine digestive physiology.

Changing hay suddenly

Even a hay-batch change can alter fibre, sugar, protein, and microbial adaptation.

Feeding large starch meals

Large grain meals increase the chance of starch reaching the hindgut.

Ignoring water intake

Dry forage plus low water intake is a classic impaction risk setup.

Feeding all horses the same

A racehorse, a retired senior, a laminitis-prone pony, and a growing youngster do not need the same ration.

Using supplements before fixing the basics

Gut supplements may help some horses, but they cannot replace forage access, clean water, gradual transitions, dental care, and appropriate calorie control.

How To Build a Forage-First Feeding Plan

A practical forage-first plan starts with the horse in front of you.

For an average adult horse in light work

• Base the diet on hay or pasture

• Use a ration balancer if needed

• Keep concentrates minimal

• Provide salt and clean water

• Monitor body condition monthly

For a hard keeper

• Check teeth, parasites, pain, ulcers, and chronic disease first

• Increase forage quality and availability

• Consider alfalfa mix, beet pulp, or fat for calories

• Split meals

• Track weight every 2 to 4 weeks

For an overweight or laminitis-prone horse

• Test hay where possible

• Use low-NSC forage

• Restrict pasture carefully

• Use a grazing muzzle or dry lot if needed

• Avoid high-starch feeds

• Provide minerals without excess calories

• Monitor digital pulses and hoof comfort

For a senior horse

• Check dental function

• Use chopped forage, soaked hay cubes, or complete feed if chewing is poor

• Do not rely only on grain

• Screen for PPID if signs fit

• Monitor weight closely

For a stabled horse

• Reduce fasting time

• Use slow feeders

• Increase movement and turnout where possible

• Provide enrichment

• Keep forage clean and available

• Avoid large concentrate meals

How To Prevent Digestive Problems

Good prevention is boring, and that is exactly why it works.

Useful habits include:

• Feed forage as the foundation

• Avoid long gaps without hay or pasture

• Keep feed changes gradual

• Split concentrate meals

• Limit starch for sensitive horses

• Provide clean water at all times

• Offer salt

• Maintain dental care

• Use fecal testing and vet-led parasite control

• Avoid sudden pasture changes

• Monitor body condition

• Watch manure daily

• Adjust forage to the individual horse

• Do not over-restrict forage in overweight horses without professional guidance

The goal is not just to prevent disease. It is to feed in a way that matches how the horse is built.

Will My Horse Be Okay?

Most horses do very well when the feeding system respects their digestive design.

If your horse has normal manure, good appetite, steady weight, a calm feeding routine, no colic history, and appropriate body condition, your forage program is probably working.

If your horse has recurrent colic, ulcers, loose manure, weight changes, stress behaviours, laminitis risk, or constant feed-related problems, the ration deserves a proper review. Often the answer is not a more complicated supplement stack. It is a simpler, steadier, forage-first plan.

FAQs

Are horses ruminants?

No. Horses are non-ruminant herbivores and hindgut fermenters. They do not have a rumen and do not chew cud. Most fibre fermentation happens in the cecum and large colon.

Why do horses need so much forage?

Forage supports chewing, saliva production, stomach buffering, hindgut fermentation, gut motility, manure quality, and normal behaviour. It is the base of equine digestive health.

Can horses live on hay alone?

Many horses in light work can do well on good-quality hay plus salt, water, and appropriate vitamin and mineral balancing. Some horses need extra calories, protein, or specialised feeds depending on workload, age, and health.

Is grain bad for horses?

Grain is not automatically bad, but large or unnecessary grain meals can increase digestive and metabolic risk. Horses with EMS, laminitis risk, ulcers, or recurrent colic often need lower-starch feeding.

How long can a horse safely go without forage?

Short gaps happen, but long fasting periods are not ideal. More than six hours without forage has been associated with increased gastric ulcer risk in stabled horses. (PMC)

Final Thoughts

Horses digest forage through a finely balanced hindgut fermentation system. That system works best when fibre arrives steadily, water is available, and feed changes are gradual.

The most important feeding principle is simple: forage first.

That does not mean every horse needs unlimited lush pasture. It means every horse needs a diet designed around fibre, gut motility, microbial stability, and the individual horse’s risk factors. Grain, fat, balancers, beet pulp, and supplements all have their place, but they should support the forage base rather than replace it.

Feed the gut you actually have in front of you: a grazing, fibre-fermenting, routine-loving hindgut machine with a strong opinion about sudden change.

If you are unsure whether your horse is getting enough forage, needs a low-starch plan, has signs of ulcers, colic risk, or hindgut upset, ASK A VET™ can help you work through the signs and decide what to do next.