How Horses Digest Food and Why Forage-First Feeding Matters

By Dr Duncan Houston

Horses are not small cows with more dramatic forelocks.

They are herbivores, but they digest food very differently from cattle, sheep, and goats. Cows ferment feed in the rumen before it reaches the true stomach. Horses have a single stomach and ferment fibre later in the digestive tract, mainly in the cecum and large colon. That makes horses hindgut fermenters, and it explains why steady forage intake is so important. Horses evolved to eat small meals for many hours each day, and their digestive system still works best when management respects that pattern. (CFAES)

The problem is that modern feeding often does the opposite. Many horses are stabled, fed twice daily, given large grain meals, and left without forage for long gaps. That mismatch can increase the risk of digestive upset, gastric ulcers, colic, hindgut disruption, weight problems, and laminitis in vulnerable horses.

Quick Answer

Horses digest forage mainly through microbial fermentation in the hindgut, especially the cecum and large colon. Microbes break down fibre from hay and pasture into volatile fatty acids, which the horse can use for energy. Because this system depends on a steady flow of fibre, horses do best on a forage-first diet, small meals, gradual feed changes, clean water, and limited large grain feeds. (Ohioline)

Are Horses Ruminants?

No. Horses are not ruminants.

Ruminants, such as cattle, sheep, and goats, have a rumen and ferment feed before it reaches the true stomach. Horses are non-ruminant, simple-stomached herbivores. Their large intestine is the main site of fermentation for fibrous feedstuffs. (CFAES)

That difference matters because a cow can ferment and reprocess feed early. A horse cannot chew cud or send feed back for another round. Once feed has moved through the stomach and small intestine, the hindgut microbes have to deal with what arrives.

In practice, the horse’s gut is designed for constant fibre flow, not long fasting followed by large starch-heavy meals.

How the Horse Digestive System Works

A horse’s digestive tract can be thought of in four main stages.

Ohio State University describes the equine stomach as relatively small, which fits the horse’s natural pattern of continuous small meals. The hindgut is comparatively large, allowing fermentation of fibrous feedstuffs that make up most of the natural equine diet. (CFAES)

The simple version is this: the stomach and small intestine handle more digestible nutrients, while the hindgut turns fibre into usable energy.

Why Chewing and Saliva Matter

Chewing is not just mechanical. It is part of digestive protection.

When a horse chews forage, it produces saliva. Saliva lubricates feed and helps buffer stomach acid. Horses can produce large volumes of saliva each day, but saliva production is linked to chewing. More forage chewing generally means more buffering support. (CFAES)

This is one reason forage access matters for gastric health. A horse standing for long periods without hay or pasture still produces stomach acid, but produces less saliva because it is not chewing.

The mistake I see most often is treating hay as optional “roughage.” For horses, forage is not garnish. It is digestive infrastructure.

What Happens in the Stomach?

The horse’s stomach is relatively small compared with the rest of the digestive tract. It is not designed to store large meals for long periods.

This matters for two reasons.

First, large meals can move through quickly and may overload later digestive stages. Second, long periods without forage can leave the stomach more vulnerable to acid exposure. A 2023 review on equine gastric ulcer syndrome notes that fibre is important because chewing increases saliva production, which helps buffer stomach acid. (PMC)

For horses at risk of gastric ulcers, feeding management often focuses on reducing long fasting periods, providing forage access, and avoiding large starch-heavy meals.

What Happens in the Small Intestine?

The small intestine is where much of the enzymatic digestion and absorption happens.

The small intestine absorbs:

• Sugars

• Starches

• Amino acids from protein

• Long-chain fatty acids

• Minerals

• Vitamins

MSD Veterinary Manual notes that sugars, amino acids, long-chain fatty acids, minerals, and vitamins are primarily absorbed in the small intestine. Nutrients that escape digestion and absorption there move on to microbial degradation in the large intestine. (MSD Veterinary Manual)

This is important for starch. A controlled amount of starch can be digested in the small intestine. Too much starch in a meal can escape into the hindgut, where it may disrupt fermentation.

What Happens in the Cecum and Large Colon?

The cecum and large colon are the fermentation engines.

They contain large populations of microbes that break down fibre. The by-products of that microbial fibre digestion are volatile fatty acids, especially acetate, propionate, and butyrate. Horses absorb these and use them as energy. (Ohioline)

This is how horses can live on hay and pasture. They are not directly digesting cellulose the way an enzyme digests starch. They are feeding a microbial population that converts fibre into usable fuel.

The clinical point is simple: protect the hindgut microbes, and you protect the horse.

Why Sudden Feed Changes Cause Problems

The hindgut microbial population is sensitive.

MSD Veterinary Manual states that microbial fermentation is sensitive to available substrates, body temperature, and pH, and that dietary changes should take place slowly over about 10 to 14 days to reduce the risk of disturbing microbial balance and causing digestive upset. (MSD Veterinary Manual)

That includes changes in:

• Hay batch

• Pasture access

• Grain type

• Grain amount

• Beet pulp

• Fat supplements

• Commercial feeds

• Haylage

• New supplements

Even changing from one hay supplier to another can matter. The horse’s gut does not read the label. It reacts to fibre type, sugar, starch, moisture, protein, digestibility, and microbial adaptation.

Why Large Grain Meals Can Be Risky

Grain is not automatically bad. Some performance horses need extra calories.

The problem is large or unnecessary grain meals, especially in horses that are not doing enough work to justify them.

High-starch or high-sugar concentrate feeding can increase digestive and metabolic risk. MSD Veterinary Manual warns that diets containing more than 50 percent high-starch or high-sugar concentrate on a dry matter basis increase the risk of laminitis, colic, and equine gastric ulcer syndrome. It also recommends limiting grain-based concentrate meal size and weighing concentrates rather than measuring by scoop. (MSD Veterinary Manual)

The real concern is undigested starch reaching the cecum and large colon. Once there, it can alter fermentation, lower pH, disrupt fibre-digesting microbes, and contribute to hindgut upset.

For some horses, the safest grain meal is the one they never needed in the first place.

How Much Forage Does a Horse Need?

Current recommendations are that horses receive at least 1.5 to 2 percent of body weight in forage per day on a dry matter basis. This can come from pasture, hay, haylage, hay cubes, hay-based pellets, beet pulp, or other high-fibre sources. (MSD Veterinary Manual)

For a 500 kg horse, that means approximately:

Hay is not completely dry, so the actual weighed amount may be slightly higher depending on moisture content.

This is a starting point, not a fixed rule for every horse. A hard keeper in work may need more. An overweight pony or laminitis-prone horse may need controlled intake, but even restricted horses still need fibre moving through the gut.

Why Water Is Part of Forage Digestion

Forage digestion depends on water.

Dry hay increases water needs. MSD Veterinary Manual notes that a 500 kg adult horse in minimal work typically drinks about 21 to 29 litres per day on a mixed hay, grain, or pasture ration, and water intake can almost double when horses are fed only dry hay. Inadequate water access can decrease feed intake and increase the risk of impaction colic, equine gastric ulcer syndrome, anhidrosis, and other disorders. (MSD Veterinary Manual)

This is why winter feeding can be risky. Horses may be eating more dry hay while drinking less cold water. That is a perfect setup for impaction colic.

Forage-first feeding is not just hay. It is hay plus water, salt, movement, and routine.

Severity Guide: How Risky Is Your Feeding Routine?

The big decision point is this: a horse with normal manure and steady condition needs management refinement; a horse with pain, laminitis signs, choke, or colic needs urgent veterinary care.

What Problems Can Poor Feeding Management Cause?

Poor feeding management does not cause every digestive disease, but it can contribute to several common problems.

Gastric Ulcers

Long periods without forage reduce chewing and saliva production. Less saliva means less buffering of stomach acid. High-concentrate feeding, intermittent feeding, stress, and exercise can all increase ulcer risk in certain horses. (PMC)

Impaction Colic

Dry forage, low water intake, reduced movement, dental disease, and sudden diet changes can contribute to impaction risk. Water access is especially important because inadequate water intake can reduce feed intake and increase impaction colic risk. (MSD Veterinary Manual)

Hindgut Upset

Too much starch reaching the hindgut can disrupt fermentation. Sudden changes in feed can also disturb microbial balance. (MSD Veterinary Manual)

Laminitis

Horses with insulin dysregulation, equine metabolic syndrome, PPID, obesity, or previous laminitis need careful control of non-structural carbohydrates from grain, pasture, and hay.

Behavioural Stress

Horses are designed to spend many hours chewing. Long fasting periods can contribute to frustration, feed anxiety, wood chewing, aggression around feed, and stereotypic behaviours in some horses.

What Else Can Look Like a Feeding Problem?

Not every digestive problem is caused by the ration.

Important rule-outs include:

Dental disease
A horse that cannot chew properly may drop feed, quid hay, lose weight, or pass poorly digested fibre.

Parasites
Parasite burdens can contribute to weight loss, poor condition, diarrhea, or colic.

Gastric ulcers
Feeding can contribute, but ulcers still need proper diagnosis and treatment.

Inflammatory bowel disease
Chronic weight loss, diarrhea, poor absorption, or low protein may need deeper investigation.

Sand accumulation
Horses fed on sandy ground may develop sand irritation or sand colic.

PPID or EMS
Older horses or easy keepers with weight changes, laminitis risk, or abnormal fat distribution may need metabolic testing.

Pain or stress
Pain, lameness, transport, herd changes, isolation, and hard work can all affect appetite and gut function.

The mistake is assuming every problem can be fixed with a new feed. Sometimes the feed is the problem. Sometimes it is only the easiest thing to blame.

When Is This an Emergency?

Call your vet urgently if your horse shows:

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

• Refusal to eat

• No manure or very reduced manure

• Severe diarrhea

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

• Sweating with abdominal pain

• 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

• Signs of dehydration

• Sudden abdominal bloating

Do not wait overnight with suspected colic, choke, laminitis, or grain overload. Those are not feeding inconveniences. They are veterinary problems.

What Should You Do Right Now?

1. Audit the Forage First

Before changing bucket feed, ask:

• How much forage is the horse actually eating?

• How many hours per day is forage available?

• Is the hay clean, appropriate, and palatable?

• Is the horse finishing hay too quickly?

• Is another horse blocking access?

• Is the horse gaining or losing weight?

• Is the manure normal?

For most horses, the forage is the main diet. The bucket feed is the adjustment.

2. Reduce Long Fasting Periods

Try to avoid long gaps without hay or pasture.

Useful options include:

• More frequent hay feeding

• Slow feeder nets

• Multiple hay piles in group turnout

• Track systems

• Hay stations

• Smaller, more frequent meals

• Turnout where safe and appropriate

The goal is not to make every horse obese on unlimited hay. The goal is to provide controlled fibre intake without long empty periods.

3. Keep Grain Meals Small

If concentrate is needed, split it into smaller meals.

MSD recommends that grain and commercial grain-based concentrates be weighed, not measured by volume. It also notes that concentrates may not be necessary when sufficient good-quality forage is available and the horse has normal dentition. (MSD Veterinary Manual)

A scoop is not a nutrition plan. Weigh it once, and the feed room suddenly becomes much more honest.

4. Make Feed Changes Gradually

Change feeds over 10 to 14 days where possible.

This includes:

• New hay

• New pasture

• New balancer

• New grain

• New fat source

• New beet pulp

• New supplement

If your horse has a sensitive gut or previous colic history, slower is better.

5. Match the Diet to the Horse

A racehorse, retired pony, broodmare, senior horse, ulcer-prone horse, and laminitis-prone horse do not need the same ration.

Ask what your horse actually needs:

• Calories?

• Protein?

• Lower starch?

• More fibre?

• Dental support?

• Weight loss?

• Weight gain?

• Ulcer management?

• Metabolic control?

Do not feed tradition. Feed the horse in front of you.

6. Provide Water and Salt

Keep clean water available at all times. Use salt or a salt source as advised.

This is especially important when horses eat mostly dry hay, sweat heavily, travel, work hard, or live in hot or cold conditions.

7. Monitor Manure

Manure is a daily report from the gut.

Watch for:

• Fewer piles than normal

• Dry manure

• Loose manure

• Free fecal water

• Undigested fibre

• Sand

• Mucus

• Diarrhea

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

Common Mistakes Owners Make

Treating grain as the main feed
For most horses, forage is the foundation. Grain is only needed when forage and a balanced ration do not meet the horse’s needs.

Leaving horses without forage for long periods
Long fasting does not match equine digestive physiology.

Changing hay suddenly
A new hay batch can change sugar, fibre, protein, digestibility, and microbial adaptation.

Feeding large starch meals
Large grain meals increase the chance of undigested starch reaching the hindgut.

Ignoring water intake
Dry hay plus poor drinking is a classic impaction risk setup.

Feeding all horses the same
The easy keeper and the hard keeper are not having the same metabolic experience.

Using supplements before fixing the basics
Gut supplements cannot replace forage, water, dental care, parasite control, and gradual feed changes.

How To Build a Forage-First Feeding Plan

For an Average Adult Horse in Light Work

Base the diet on suitable hay or pasture. Add salt, clean water, and a ration balancer if needed. Many light-work horses do not need a calorie-heavy concentrate.

For a Hard Keeper

Check teeth, parasites, pain, ulcers, and chronic disease first. Then improve forage quality, increase calorie density gradually, and consider beet pulp, alfalfa mix, fat, or a suitable senior or performance feed.

For a Laminitis-Prone or EMS Horse

Use tested low-NSC forage where possible. Restrict pasture carefully. Avoid high-starch feeds. Use a balancer for minerals and amino acids without unnecessary calories. Monitor digital pulses and hoof comfort closely.

For a Senior Horse

Assess dental function. If chewing hay is poor, use soaked hay cubes, chopped forage, beet pulp, or a complete senior feed designed to replace forage. Do not simply add more grain.

For a Stabled Horse

Reduce fasting time. Use slow feeders, safe turnout, movement, enrichment, and frequent forage feeding. Long stable hours plus large concentrate meals is not a gut-friendly routine.

How To Prevent Digestive Problems

Good prevention is practical and consistent.

Helpful 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

• Match forage and feed to the individual horse

• Do not over-restrict forage in overweight horses without veterinary or nutrition guidance

The best feeding plan is not complicated. It is consistent, measured, forage-based, and adapted to the horse’s risk factors.

Will My Horse Be Okay?

Most horses do very well when their diet matches their digestive design.

If your horse has normal manure, steady weight, good appetite, appropriate body condition, and no recurring colic or ulcer signs, your feeding routine is probably working.

If your horse has recurrent colic, loose manure, free fecal water, weight loss, poor topline, girthiness, ulcer signs, stress behaviours, or laminitis risk, the ration deserves a proper review. Often the solution is not a more exciting supplement. It is a steadier forage-first plan.

FAQs

Are horses hindgut fermenters?

Yes. Horses are hindgut fermenters, which means the large intestine, especially the cecum and large colon, is the main site of fibre fermentation. (CFAES)

Why do horses need forage all day?

Forage supports chewing, saliva production, stomach buffering, gut motility, hindgut fermentation, manure quality, and normal behaviour. Horses evolved to eat small meals for many hours each day. (CFAES)

Can horses live on hay alone?

Many horses in light work can do well on good-quality forage plus salt, clean water, and appropriate vitamin and mineral balancing. Others need extra calories, protein, or specialised feed depending on age, workload, dental health, and medical status.

Is grain bad for horses?

Grain is not automatically bad. It can be useful for horses with high energy needs. It becomes risky when fed in large meals, fed unnecessarily, or given to horses prone to ulcers, colic, EMS, insulin dysregulation, or laminitis.

How quickly can I change my horse’s feed?

Most feed changes should be made gradually over about 10 to 14 days to give hindgut microbes time to adapt. Sudden changes increase the risk of digestive upset. (MSD Veterinary Manual)

Final Thoughts

The horse’s digestive system is built around steady forage intake and hindgut fermentation.

That does not mean every horse needs unlimited lush pasture. It means every horse needs a feeding plan that respects fibre, chewing, saliva, water, microbial balance, and gradual change.

Forage should be the foundation. Grain should be used only when it solves a real nutritional problem. Water should never be an afterthought. Feed changes should be slow. And the horse in front of you should always matter more than tradition.

The best feeding plans are not flashy. They are steady, measured, and built around how the equine gut actually works.

If you are unsure whether your horse is getting enough forage, eating too much starch, showing signs of ulcers, developing colic risk, or needs a safer feeding plan, ASK A VET™ can help you work through the signs and decide what to do next.