How To Prevent Enteroliths in Horses

By Dr Duncan Houston

Enteroliths are intestinal stones that can cause recurrent colic, sudden obstruction, and in serious cases, life-threatening bowel damage.

Enteroliths are one of the more frustrating causes of colic because they often build slowly and silently. A horse may seem normal for months or years, then start having vague, intermittent colic episodes, or suddenly develop a more severe obstruction.

The good news is that while enteroliths cannot always be prevented completely, the risk can often be reduced with smarter feeding, more movement, better turnout, and cleaner management.

The key is not one magic supplement. It is building a daily routine that makes the large colon less favourable for stone formation.

Quick Answer

Enteroliths are mineral stones that form inside the horse’s intestine, usually around a small foreign object such as a pebble, metal fragment, hair, rubber, or baling twine. They are most strongly linked with alfalfa-rich diets, certain breed predispositions, limited turnout, reduced gut movement, and mineral-rich intestinal conditions. Reducing alfalfa, increasing pasture or grass hay, encouraging daily movement, avoiding bran and mineral-heavy feeds, and keeping feeding areas clean can help lower the risk. If a horse develops repeated, worsening, or severe colic, this should be treated as urgent because obstructing enteroliths generally require surgical removal. (Center for Equine Health)

What Are Enteroliths?

Enteroliths are stone-like mineral accumulations that form inside the bowel, most commonly in the large colon.

They usually form around a central object, known as a nidus. This may be something small the horse has swallowed, such as:

1. A pebble

2. A piece of metal

3. Baling twine

4. Hair

5. Rubber

6. Plant material or other debris

Over time, minerals build up around that centre in layers. UC Davis describes enteroliths as accumulations of magnesium-ammonium-phosphate, also called struvite, that can form round, flat, or triangular stones in the bowel over multiple years. (Center for Equine Health)

Small enteroliths may pass in manure without causing illness. Larger stones are the concern. They can sit quietly for a long time, then shift position and block the large colon or small colon, causing colic.

Why Are Enteroliths Dangerous?

The danger is obstruction.

A horse’s intestine is long, mobile, and sensitive to changes in flow. If a stone blocks the movement of feed, fluid, and gas, pressure builds behind the obstruction. That can cause pain, reduced blood supply, bowel wall damage, and in the worst cases, rupture.

The real concern is not simply that the stone exists. The concern is whether it is large enough, mobile enough, or positioned badly enough to obstruct the bowel.

In practice, enteroliths often sit in the background until they create one of two patterns:

1. Recurrent mild colic
   The horse has repeated episodes of discomfort that seem to resolve, then return.

2. Acute obstructive colic
   The horse becomes painful, may stop passing manure, may become sweaty or distressed, and does not settle normally.

UC Davis notes that early diagnosis matters because an obstructing enterolith can lead to intestinal rupture with fatal consequences. (Center for Equine Health)

What Causes Enteroliths To Form?

Enterolith formation is not fully understood. That is important. It is not as simple as saying, “alfalfa causes stones” or “one feed change prevents them.”

The current understanding is that enteroliths form when several risk factors overlap:

1. A central object is swallowed

2. Minerals are available in the colon

3. The intestinal environment favours mineral layering

4. Gut motility is reduced or altered

5. The horse has individual or breed susceptibility

The major risk factors are diet, management, breed, and movement.

The Biggest Diet Risk: Too Much Alfalfa

Alfalfa is one of the strongest dietary associations with enterolith formation.

Alfalfa is rich in minerals and protein, and alfalfa-heavy diets can contribute to a colon environment that favours stone formation. Research has linked reduced alfalfa intake and daily pasture access with lower risk of enterolithiasis. (PubMed)

This does not mean every horse eating alfalfa will develop enteroliths. Many horses eat alfalfa without ever forming stones. But in an at-risk horse, especially one with recurrent colic, a high-alfalfa diet deserves serious attention.

A practical rule:

If your horse is at risk of enteroliths, grass hay or pasture should usually form the main forage base, not alfalfa.

UC Davis recommends cutting down alfalfa so it makes up less than 50 percent of the diet for prevention, and horses that have had enterolith surgery should not have alfalfa in their diet. (Center for Equine Health)

Why Grass Hay And Pasture Matter

Grass hay and pasture support a more natural forage pattern.

They help by:

1. Increasing chewing time

2. Supporting gut movement

3. Encouraging water intake through normal forage digestion

4. Reducing reliance on mineral-rich feeds

5. Keeping the digestive tract moving more consistently

Pasture also adds movement. A horse grazing across a paddock is not just eating differently. It is walking, stretching, hydrating, browsing, and keeping the gut active.

That matters because enterolith risk is not only about what goes into the horse. It is also about how long material sits inside the colon.

Limited Turnout Increases Risk

Horses kept indoors for long periods appear to be at higher risk.

A study of horses in Texas found increased risk in horses fed alfalfa hay, horses spending 50 percent or less of their time outdoors, and horses of certain breeds, including Arabians and Miniatures. (PubMed)

This makes clinical sense. Less turnout often means:

1. Less grazing

2. Less walking

3. More meal-based feeding

4. Less gut stimulation

5. Higher risk of boredom behaviours such as chewing bedding, wood, or foreign material

Movement is not a decorative management extra. For horses, it is part of digestive health.

Which Horses Are Most At Risk?

Enteroliths can occur in any horse, but some groups appear overrepresented.

Higher-risk horses may include:

1. Arabians and Arabian crosses

2. Morgans

3. American Saddlebreds

4. Miniature horses

5. Horses with a history of recurrent colic

6. Horses on alfalfa-rich diets

7. Horses with limited turnout

8. Horses in regions where enteroliths are more common

UC Davis notes that Arabians, Arabian crosses, Morgans, and American Saddlebreds appear overrepresented, and enterolithiasis is reported worldwide but more common in some regions, including California and Florida. (Center for Equine Health)

Breed risk does not mean inevitability. It means the threshold for prevention and investigation should be lower.

Signs Of Enterolith Colic

Enteroliths can cause vague signs before a dramatic episode.

Possible signs include:

1. Recurrent mild colic

2. Pawing

3. Looking at the flank

4. Lying down and getting up repeatedly

5. Rolling

6. Sweating

7. Reduced appetite

8. Weight loss

9. Loose manure or changes in manure

10. Girthiness

11. Lethargy

12. Reluctance to exercise

UC Davis notes that clinical signs vary depending on stone size, number, and location. Large stones in the large colon may cause chronic intermittent colic, while smaller stones that lodge in the small colon may cause more acute signs. (Center for Equine Health)

In practice, the pattern matters. A single mild bellyache may be many things. Recurrent colic in the same horse deserves a deeper look.

How Worried Should You Be?

Risk Level	What It Looks Like	What It May Mean	What To Do
Low risk	Horse is bright, eating, passing normal manure, no colic signs, but has some dietary risk factors	Risk may be manageable with prevention	Review diet, reduce alfalfa reliance, increase turnout and movement
Medium risk	Occasional mild colic, reduced appetite, vague discomfort, intermittent manure changes	Possible early or unrelated digestive issue	Arrange a veterinary review, especially if episodes repeat
High risk	Recurrent colic, repeated episodes after feeding, signs return after pain relief, reduced manure output	Possible obstructive or recurring intestinal problem	Veterinary assessment is needed. Do not keep treating repeatedly at home
Critical	Severe pain, rolling, sweating, persistent colic, no manure, bloated abdomen, dullness, abnormal gums, high heart rate	Possible obstruction, bowel compromise, or surgical colic	Emergency veterinary care immediately

The most important checkpoint is this:

A horse with colic that does not settle, keeps recurring, or needs repeated pain relief should not be treated as routine.

What Else Can Look Like Enterolith Colic?

Enteroliths are only one cause of colic. A good article should not pretend every recurrent colic case is an intestinal stone.

Other important causes include:

1. Large colon impaction

2. Sand accumulation

3. Gas colic

4. Large colon displacement

5. Strangulating obstruction

6. Small intestinal obstruction

7. Parasite-associated disease

8. Right dorsal colitis

9. Gastric ulcers

10. Dental disease affecting chewing and fibre digestion

11. Sudden diet change

12. Poor water intake

13. Toxin or feed contamination

This is why diagnosis matters. Colic is a clinical sign, not a diagnosis.

The mistake owners often make is focusing only on stopping pain. The better question is: why is this horse painful, and is the bowel still safely moving?

How Do Vets Diagnose Enteroliths?

Diagnosis can be challenging because the signs are not specific.

Your vet may consider:

1. History of recurrent colic

2. Diet history, especially alfalfa intake

3. Breed and regional risk

4. Physical examination

5. Heart rate and hydration status

6. Gut sounds

7. Rectal examination where appropriate

8. Nasogastric reflux assessment where indicated

9. Abdominal radiographs

10. Referral for hospital workup

11. Exploratory surgery in urgent or unclear cases

Radiographs are considered the best screening test for enteroliths, although they do not find every case. Detection depends on the horse’s size, bowel contents, stone location, and equipment used. (Center for Equine Health)

In some cases, surgery provides the definitive diagnosis.

When Is This An Emergency?

Colic should always be taken seriously, but some signs are clear red flags.

Treat it as an emergency if your horse shows:

1. Repeated rolling or violent discomfort

2. Sweating with abdominal pain

3. Pain that does not improve or quickly returns

4. No manure or markedly reduced manure

5. Distended abdomen

6. Dullness, weakness, or collapse

7. High heart rate

8. Pale, dark red, purple, or tacky gums

9. Repeated lying down and getting up

10. Colic signs after a known history of recurrent episodes

MSD Veterinary Manual notes that horses with severe abdominal pain that do not respond to analgesic treatment generally require emergency abdominal surgery, and enterolithiasis is one possible cause of complete obstruction. (MSD Veterinary Manual)

Do not wait overnight to see if severe colic improves. Horses can deteriorate quickly.

What Should You Do Right Now If You Suspect A Problem?

Step 1: Call your vet early

If your horse has colic signs, call your veterinarian. Describe the signs clearly:

1. When the signs started

2. Whether the horse is eating

3. Whether manure is being passed

4. Whether the horse is sweating or rolling

5. Any previous colic episodes

6. Current diet, especially alfalfa intake

7. Any recent feed or turnout changes

Step 2: Remove feed until advised

Do not keep feeding a horse that may have an obstruction. Your vet can advise whether water should remain available based on the situation.

Step 3: Keep the horse safe

If the horse is rolling violently, safety becomes the priority. Do not put yourself between a painful horse and a wall, fence, float, or stable door.

Step 4: Do not repeatedly medicate without reassessment

Pain relief can be appropriate, but repeated medication without a diagnosis can delay referral. The concern is not whether the horse looks better for an hour. The concern is whether the underlying obstruction is still there.

Step 5: Escalate if signs return

If the horse improves, then becomes painful again within a few hours, that is a major warning sign.

How To Reduce Enterolith Risk Through Nutrition

Prevention is about changing the intestinal environment and management pattern.

1. Make grass hay or pasture the main forage

For at-risk horses, base the diet around quality grass hay and pasture where possible.

This helps reduce reliance on alfalfa and supports normal gut motility.

2. Reduce or remove alfalfa in high-risk horses

If your horse is an Arabian, Morgan, Saddlebred, Miniature, has recurrent colic, or has previously had enteroliths, alfalfa should be reviewed carefully.

For horses with a previous enterolith, alfalfa is usually best avoided completely unless your treating veterinarian has a specific reason otherwise.

3. Avoid routine bran feeding

Bran has historically been used in horses for digestive support, but it is not a magic gut cleaner. UC Davis recommends reducing or eliminating bran as part of enterolith prevention. (Center for Equine Health)

4. Review mineral intake

Avoid stacking mineral-rich feeds, supplements, and hays without knowing the total diet.

A proper ration review matters more than adding another supplement to an already unbalanced plan.

5. Increase feeding frequency

More frequent smaller feeds can help reduce long periods of gut inactivity.

For horses, the gut is designed for steady intake, not long fasting followed by large meals.

6. Encourage water intake

Hydration supports normal intestinal movement.

Practical steps include:

1. Clean water troughs

2. Multiple water points where needed

3. Salt access where appropriate

4. Wetting feed if advised

5. Monitoring intake during hot weather or travel

7. Increase turnout and daily movement

Daily movement helps gut motility.

This can include:

1. More paddock time

2. Hand walking during restricted periods

3. Regular exercise

4. Grazing time where safe

5. Reducing unnecessary stall confinement

8. Keep feeding areas clean

Because enteroliths form around a central object, reducing foreign material ingestion is sensible.

Check for:

1. Baling twine

2. Wire fragments

3. Small stones in feed areas

4. Rubber pieces

5. Bedding contamination

6. Loose hardware

7. Sand or gravel contamination

In sandy areas, feed on clean mats, safe feeders, or surfaces that reduce sand and debris ingestion.

Can Apple Cider Vinegar Prevent Enteroliths?

Apple cider vinegar is sometimes discussed because acidifying the intestinal environment may theoretically help reduce favourable conditions for stone formation.

UC Davis lists adding apple cider vinegar to hay or grain as one management step used in prevention plans. (Center for Equine Health)

But this should not be oversold. Apple cider vinegar is not a cure, and it should not be the main prevention strategy. The bigger foundations are forage choice, reducing alfalfa in at-risk horses, increasing turnout, encouraging movement, and removing foreign material from feeding areas.

In practice, I would treat apple cider vinegar as a possible supporting measure, not the centre of the plan.

Can Psyllium Help?

Psyllium is sometimes used in horses at risk of sand accumulation or intestinal debris.

UC Davis lists psyllium supplementation as one additional management step that may help prevent enterolith formation. (Center for Equine Health)

The practical point is this: psyllium may be useful in selected horses, especially in sandy environments, but it should not be used as a substitute for correcting the diet and management pattern.

Common Mistakes Owners Make

1. Waiting too long with recurrent colic

Repeated mild colic is not normal. If it keeps happening, investigate it.

2. Assuming alfalfa is always harmless because the horse looks well

Alfalfa can be useful in some feeding plans, but in enterolith-prone horses, it needs careful review.

3. Using pain relief repeatedly without diagnosis

A horse that needs repeat colic medication may need referral, imaging, or surgery.

4. Ignoring manure changes

Reduced manure, dry manure, loose manure, or straining can all help build the clinical picture.

5. Adding supplements before fixing the base diet

The foundation is forage, movement, water, and management. Supplements come after that, not before.

6. Forgetting to check the environment

Baling twine, wire, rubber, stones, and debris can become the centre point for mineral layering.

Prevention Plan For At-Risk Horses

If your horse is at higher risk, use this as a practical starting framework.

Prevention Area	What To Do	Why It Matters
Forage	Base diet on grass hay and pasture	Reduces reliance on alfalfa-rich mineral intake
Alfalfa	Reduce sharply or avoid in high-risk horses	Alfalfa-rich diets are strongly associated with risk
Turnout	Increase daily turnout where possible	Supports gut movement and grazing behaviour
Exercise	Maintain consistent movement	Helps intestinal motility
Feeding pattern	Use smaller, more frequent meals	Reduces long periods of gut inactivity
Water	Keep clean water available and monitor intake	Supports hydration and gut flow
Environment	Remove twine, wire, rubber, stones, and debris	Reduces possible central objects for stone formation
Monitoring	Track colic episodes, appetite, manure, and behaviour	Helps detect patterns early

What If Your Horse Has Already Had An Enterolith?

A horse that has already had an enterolith should be managed as high risk.

The prevention plan becomes stricter:

1. Avoid alfalfa unless your veterinarian specifically advises otherwise

2. Use grass hay or pasture as the forage base

3. Increase turnout and daily movement

4. Avoid bran and unnecessary mineral-heavy feeds

5. Review the full ration with your veterinarian or equine nutritionist

6. Keep feeding areas very clean

7. Investigate any future colic early

UC Davis notes that recurrence is highly likely if recommended dietary changes are not followed after surgery. (Center for Equine Health)

That is the critical message: surgery removes the stone, but management reduces the chance of the same problem returning.

Will A Horse Be Okay After Enterolith Surgery?

Many horses can recover well if the obstruction is detected and treated before serious bowel damage occurs.

UC Davis reports that full recovery is very likely for larger enteroliths when resulting impactions are identified before colon damage, and early detection followed by surgical removal has a high success rate. (Center for Equine Health)

Outcome depends on:

1. How early the problem is recognised

2. Where the stone is lodged

3. Whether the bowel is damaged

4. Whether rupture or severe contamination has occurred

5. The horse’s overall health

6. How quickly surgery happens when needed

This is why delayed referral is risky. Colic surgery outcomes are often better when the decision is made before the horse is exhausted, shocky, or metabolically unstable.

Helpful Related Reading

This topic links closely with:

1. Horse colic signs and when to call a vet

2. When a horse needs colic surgery

3. Sand colic prevention

4. Feeding horses with recurrent colic

5. Right dorsal colitis from NSAID use

6. Safe use of phenylbutazone and flunixin in horses

These articles work well as an internal equine health cluster because enteroliths are part of the broader colic risk conversation.

FAQs

Can enteroliths in horses be prevented completely?

Not always. Some horses develop enteroliths despite good management. However, reducing alfalfa, increasing grass hay or pasture, improving turnout, encouraging movement, and keeping feeding areas clean can reduce risk.

Is alfalfa bad for every horse?

No. Alfalfa can be useful for some horses, especially those needing extra calories or protein. The concern is mainly with alfalfa-heavy diets in horses already at higher risk of enteroliths.

What is the first sign of enteroliths in horses?

The first sign may be recurrent mild colic. Some horses show vague signs such as reduced appetite, loose manure, girthiness, lethargy, or reluctance to exercise before obvious colic appears.

Can enteroliths pass in manure?

Small enteroliths can sometimes pass in manure without causing illness. Larger stones are more dangerous because they can obstruct the bowel and cause colic.

Do enteroliths always need surgery?

If an enterolith is causing colic or obstruction, surgical removal is generally required. Small stones may pass naturally, but once a horse is clinically affected, this is not a home-treatment situation.

Final Thoughts

Preventing enteroliths is not about chasing one perfect feed additive. It is about reducing the conditions that allow stones to form.

For most horses, that means more grass hay or pasture, less reliance on alfalfa, cleaner feeding areas, better hydration, more movement, and earlier investigation when colic keeps coming back.

The horse that worries me most is not always the one with the loudest single colic episode. It is often the horse with a pattern: mild colic, recovery, then another episode, then another. That pattern deserves attention before it becomes an obstruction.

Enterolith prevention is quiet, daily management. But when it works, it may prevent one of the most serious forms of colic a horse can face.

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If your horse has recurrent colic, a history of enteroliths, or you are unsure whether their diet is increasing risk, ASK A VET™ can help you understand what to monitor, what questions to ask your veterinarian, and when the signs should be treated as urgent.