How To Prevent Enteroliths in Horses

How To Prevent Enteroliths in Horses

By Dr Duncan Houston

Enteroliths are one of those conditions many horse owners do not think about until a horse has repeated colic episodes or suddenly needs surgery.

They are intestinal stones that form inside the colon. Some stay small and never cause obvious signs. Others grow large enough to partially or completely block the intestine, causing colic that may become life-threatening if the bowel becomes damaged or ruptures. UC Davis describes enteroliths as intestinal stones that form within the colon and can obstruct the intestine, resulting in colic. (Center for Equine Health)

The frustrating part is that enteroliths are not completely understood. Some horses develop them, others do not, even under similar management. But there are clear risk factors we can reduce, especially high-alfalfa diets, lack of pasture access, limited turnout, mineral-rich diets, and exposure to small foreign objects that can become the core of a stone. (ScienceDirect)

Quick Answer

Enteroliths are mineral stones that form in the horse’s intestine and can cause partial or complete obstruction, leading to colic. The best prevention strategy is to reduce known risk factors: avoid feeding more than half the diet as alfalfa, increase grass hay or pasture where appropriate, provide regular turnout and exercise, reduce bran and excess mineral-rich feeds, avoid ground feeding in sandy or dirty areas, and manage any recurrent colic signs seriously. (Center for Equine Health)

If your horse has repeated colic episodes, severe abdominal pain, reduced manure, sweating, rolling, depression, or pain that does not respond to treatment, call your vet urgently. Enterolith-related obstruction often requires surgical removal. (Center for Equine Health)

What Are Enteroliths?

Enteroliths are rock-like mineral concretions that form inside the horse’s intestine, most commonly in the large colon.

They usually form in layers around a central core, called a nidus. That core may be a small stone, wire, twine, piece of cloth, hair, or another foreign object that the horse has swallowed. Over time, minerals deposit around it, forming a stone that can become smooth, round, triangular, or flat-sided. Flat or triangular enteroliths can suggest that more than one stone is present, because they can rub against each other inside the gut. (Center for Equine Health)

Many equine enteroliths are made largely of struvite, which is magnesium ammonium phosphate. The conditions that favour formation appear to include mineral availability, nitrogen, and a more alkaline environment in the colon. (ScienceDirect)

In simple terms, an enterolith is not just “a rock the horse ate.”

It is a stone the horse’s gut has built over time, usually around something small that should not have been there in the first place.

Why Enteroliths Cause Colic

Small enteroliths may pass in manure or sit quietly without causing obvious signs.

The problem starts when an enterolith becomes large enough to interfere with movement of feed, fluid, and gas through the intestine. It may cause intermittent blockage, where the horse has repeated colic episodes that seem to improve and then return. Or it may lodge completely, causing a full obstruction. (Center for Equine Health)

The most dangerous situation is complete obstruction. Gas and intestinal contents build up behind the blockage, pressure increases, blood flow to the bowel can be compromised, and the intestine may rupture. UC Davis notes that rupture before detection and removal is fatal, and that enteroliths slightly larger than a fecal ball are particularly concerning because they can completely obstruct the small colon, a site predisposed to rupture. (Center for Equine Health)

That is why recurrent or severe colic should never be brushed off as “just gas again.”

Sometimes it is gas.

Sometimes it is a stone slowly turning the gut into a plumbing problem with hooves.

Why Alfalfa Is Linked to Enterolith Risk

Alfalfa is not evil.

It can be an excellent forage for many horses. It is high in protein, calcium, and digestible nutrients, and it can be very useful for lactating mares, growing horses, poor doers, and horses needing higher-quality forage.

But high-alfalfa diets are one of the best-documented risk factors for enterolithiasis.

A California case-control study found that feeding 50% or more of the diet as alfalfa was significantly associated with enterolithiasis. The same study found that feeding less than 50% of the diet as grass hay or oat hay, and lack of daily pasture access, were also significantly associated with enterolith risk. (ScienceDirect)

The suspected mechanism is practical: alfalfa contributes to a more alkaline colonic environment and provides more nitrogen and magnesium, which may support struvite enterolith formation. (ScienceDirect)

So the message is not “never feed alfalfa.”

The message is: do not build a high-risk horse’s entire forage plan around alfalfa, especially if the horse lives in an enterolith-prone region or has a previous enterolith history.

Which Horses Are Higher Risk?

Enteroliths can occur in any horse, but the risk is not equal in every horse.

Higher-risk situations include:

• Horses fed high-alfalfa diets

• Horses with 50% or more of the diet as alfalfa

• Horses with little or no daily pasture access

• Horses with limited turnout or stall confinement

• Horses in regions where enteroliths are more common, including parts of California

• Horses with recurrent colic

• Horses that have had enteroliths before

• Horses exposed to foreign objects in feed, bedding, paddocks, or hay

• Horses eating off sandy, dirty, rocky, or contaminated ground

• Horses receiving mineral-rich feeds or bran-heavy diets without a clear need

UC Davis notes that enterolith formation can involve diet, breed predisposition, and management, but also stresses that it is not fully understood why some horses develop enteroliths while others do not. (Center for Equine Health)

That uncertainty matters. It means prevention is about reducing risk, not making guarantees.

Are Enteroliths Common?

Enteroliths are not the most common cause of colic in every region.

They are seen worldwide, but they are much more common in certain geographic areas. UC Davis notes that enterolithiasis is especially prevalent in some locations, including California, and that veterinarians in these regions may suspect stones in horses with a history of colic. (Center for Equine Health)

This changes how suspicious I would be.

A horse in a low-risk region with one mild gas colic episode does not immediately scream enterolith.

A horse in a high-risk region, eating mostly alfalfa, with repeated colic episodes that resolve and return, deserves a much more serious look.

Signs of Enteroliths in Horses

Enterolith signs can be frustrating because they often look like “normal colic.”

Possible signs include:

• Repeated mild colic episodes

• Pawing

• Looking at the flank

• Rolling

• Sweating

• Reduced appetite

• Reduced manure

• Abdominal discomfort after eating

• Lying down more than normal

• Depression

• Pain that improves then returns

• Severe pain if obstruction becomes complete

• Distended abdomen in some cases

• Fever or worsening depression if bowel damage develops

The pattern matters. Recurrent colic is a big clue.

A horse that colics once after a feed change may have many possible causes. A horse that colics repeatedly over weeks or months, especially with an alfalfa-heavy diet or previous enterolith history, should be investigated more thoroughly.

Risk Framework: How Worried Should You Be?

Low Risk

This is usually lower risk if your horse:

• Has no history of colic

• Eats mostly grass hay or pasture

• Has limited or no alfalfa

• Has daily turnout

• Has clean feeding areas

• Does not eat from sandy or dirty ground

• Has normal appetite, manure, water intake, and behaviour

This horse does not need panic. Basic colic-prevention management is appropriate.

Moderate Risk

This is more concerning if your horse:

• Eats a mixed diet with regular alfalfa

• Has limited pasture access

• Is stalled for long periods

• Has occasional mild colic

• Eats from the ground in sandy or rocky areas

• Has unknown hay or mineral intake

• Has inconsistent exercise or turnout

This is the stage where prevention changes are sensible: reduce alfalfa load, increase grass hay, improve turnout, clean up feeding areas, and monitor colic patterns.

High Risk

This is high risk if your horse:

• Eats 50% or more of the diet as alfalfa

• Has repeated colic episodes

• Lives in an enterolith-prone region

• Has had an enterolith before

• Has little or no daily turnout

• Receives bran or mineral-heavy feeds without a clear reason

• Has access to wire, stones, twine, rope, or foreign material

• Has colic that keeps returning after apparent improvement

This horse needs a veterinary review and a prevention plan, not just “watch and wait.”

Critical

This is urgent if your horse:

• Has severe colic pain

• Rolls violently

• Sweats heavily

• Has pain that does not improve or returns quickly

• Has reduced or absent manure

• Has abdominal distension

• Has depression or weakness

• Has fever

• Has abnormal gum colour

• Has a high heart rate

• Is deteriorating over hours

This horse needs urgent veterinary attention. A complete obstruction can become life-threatening quickly. AAEP stresses that colic can become life-threatening in a relatively short period of time and should never be ignored.

When Is This an Emergency?

Treat colic as an emergency if your horse shows:

• Repeated rolling

• Violent pain

• Sweating

• Pawing that does not settle

• Flank-watching with worsening discomfort

• Repeated lying down and getting up

• Loss of appetite

• No manure or markedly reduced manure

• Severe depression

• Abdominal distension

• High heart rate

• Pale, purple, brick-red, or very dry gums

• Pain that returns after medication

• Signs that worsen over a few hours

Merck Veterinary Manual notes that surgery is usually necessary when there is a mechanical obstruction that cannot be corrected medically, when blood supply is compromised, or when severe pain does not respond to pain medication. (Merck Veterinary Manual)

If an enterolith is causing obstruction, waiting can be dangerous. UC Davis states that the only successful treatment for horses with colic due to enteroliths is surgical removal. (Center for Equine Health)

How Vets Diagnose Enteroliths

Diagnosis can be straightforward in some horses and difficult in others.

Your vet may use:

• History and diet review

• Physical examination

• Heart rate and gum assessment

• Rectal examination

• Nasogastric intubation if indicated

• Abdominal ultrasound

• Abdominal radiographs

• Bloodwork

• Response to pain relief and fluids

• Referral hospital assessment

• Exploratory surgery if obstruction is suspected

Radiographs are often the best screening test for enteroliths, but they do not find every case. UC Davis notes that detection depends on the size of the horse, feed contents in the bowel, location of the stone, and radiographic equipment. Stones in the large colon may be easier to detect than those in the small colon. (Center for Equine Health)

In large horses, abdominal radiographs can be technically difficult. In some cases, the enterolith is only confirmed at surgery.

That is why repeated colic history matters. The vet is not just treating today’s pain. They are looking for the pattern behind it.

What Else Can Look Like Enterolith Colic?

Not every horse with repeated colic has enteroliths.

Important rule-outs include:

• Gas colic

• Large colon impaction

• Sand colic

• Parasite-associated colic

• Gastric ulcers

• Large colon displacement

• Small intestinal obstruction

• Enteritis or colitis

• Dental disease causing poor chewing and impaction risk

• Poor water intake

• Feed changes

• Grain overload

• Toxic plants

• Blister beetle exposure

• Strangulating lesions

• Right dorsal colitis

• Reproductive or urinary pain that mimics colic

This is why the details matter.

Tell your vet about hay type, alfalfa percentage, pasture access, turnout, exercise, recent feed changes, manure patterns, sand exposure, recurrent colic episodes, and whether the horse has passed any stone-like material in manure.

The more complete the history, the better the diagnostic pathway.

How Are Enteroliths Treated?

If an enterolith is causing colic from obstruction, treatment is surgical removal.

Medical treatment may temporarily help pain in some cases, but it does not remove a large stone. UC Davis states clearly that the only successful treatment for horses with colic due to enteroliths is surgical removal. Horses are generally kept out of work for about three months after surgery, and horses that have had enterolith surgery should not have alfalfa in their diets. (Center for Equine Health)

The prognosis can be good when the obstruction is identified and treated before serious bowel damage occurs. UC Davis reports that early detection and surgical removal have a high success rate, but rupture before detection is fatal. (Center for Equine Health)

That is the whole game: catch it before the bowel is compromised.

What Should You Do Next?

1. Take Recurrent Colic Seriously

One mild colic episode may not mean enteroliths.

Repeated colic episodes are different.

If your horse has had multiple colics, especially if they are on a high-alfalfa diet or live in an enterolith-prone region, ask your vet whether enteroliths should be on the rule-out list.

Do not keep treating each episode as a separate random event if there is a pattern.

2. Review the Alfalfa Percentage

Work out how much of the total diet is alfalfa.

This includes:

• Alfalfa hay

• Alfalfa cubes

• Alfalfa pellets

• Chaff

• Mixed hay containing alfalfa

• Complete feeds with alfalfa meal

• Treats or supplements with alfalfa

For at-risk horses, UC Davis recommends cutting down on alfalfa so that it makes up less than 50% of the diet. (Center for Equine Health)

For horses that have already had enterolith surgery, UC Davis advises no alfalfa in the diet. (Center for Equine Health)

3. Increase Grass Hay or Pasture Where Appropriate

Grass hay and pasture may help reduce risk by changing the forage base and supporting more normal gut movement.

The California case-control study found that lack of daily pasture grazing was significantly associated with enterolithiasis, and the authors suggested that decreasing alfalfa and allowing daily pasture access might reduce risk. (ScienceDirect)

This does not mean every horse can safely have lush pasture. Horses with EMS, obesity, insulin dysregulation, or laminitis risk need a separate pasture plan.

The principle is to move away from a high-alfalfa, stall-bound setup when possible.

4. Reduce Bran and Unnecessary Mineral-Rich Feeds

Bran and mineral-heavy feeds have long been discussed as possible contributors because of their mineral content, although not every suspected factor has been fully proven.

UC Davis lists reducing or eliminating bran and avoiding mineral-rich feeds as prevention steps for enterolith management. (Center for Equine Health)

The sensible approach is:

Do not feed bran, extra minerals, or multiple supplements without a clear reason.

Test forage when needed.

Balance the ration properly.

Do not let the feed bucket become a mineral lucky dip.

5. Keep Feed Away From Sand, Stones, Wire, and Foreign Objects

Because enteroliths often form around a nidus, reducing foreign-object exposure is sensible.

Check for:

• Wire fragments

• Twine

• Rope

• Nails

• Screws

• Small stones

• Metal debris

• Plastic

• Cloth fragments

• Contaminated hay

• Dirty feed areas

• Sandy feeding areas

AAEP’s colic-prevention guidance recommends avoiding feed on the ground, especially in sandy soils, and checking hay, bedding, pasture, and the environment for toxic substances and ingestible foreign matter.

This is boring paddock management, which is exactly why it works.

6. Increase Turnout and Exercise

Movement helps support normal gut motility.

UC Davis lists additional grazing, increasing feedings per day, and frequent consistent exercise as management steps that can help keep food material moving through the colon. (Center for Equine Health)

AAEP also recommends daily exercise or turnout as part of colic-risk reduction.

This does not mean every horse needs hard exercise. It means stall confinement and long periods of immobility are not ideal for gut health.

The gut likes routine. The horse likes movement. The stable schedule often likes neither.

7. Feed More Frequent, Smaller Meals

Large, infrequent meals can be hard on the digestive system.

For enterolith-prone horses, smaller, more frequent forage-based meals may help keep gut contents moving more consistently. UC Davis includes increasing the number of feedings per day among prevention strategies. (Center for Equine Health)

AAEP also recommends dividing concentrate rations into smaller feedings rather than one large meal, and feeding a diet primarily based on roughage.

8. Discuss Psyllium if Sand Is Also a Concern

Psyllium is not an enterolith dissolver.

It may be useful in some horses at risk of sand accumulation or impactions, depending on the environment and veterinary advice. Merck notes that psyllium may be used in horses living in sandy environments or horses that persistently develop impactions, as directed by a veterinarian. (Merck Veterinary Manual)

If your horse lives in a sandy area and is also enterolith-prone, ask your vet whether a sand-management plan makes sense.

9. Be Careful With Apple Cider Vinegar Claims

Apple cider vinegar is often discussed for enterolith prevention because it may slightly acidify colonic contents.

UC Davis lists apple cider vinegar as one possible management step. However, the evidence is not strong enough to treat it as a guaranteed prevention method. Diana Hassel, DVM, PhD, notes that studies showed some acidification of gut contents, but we still do not know whether that extra acidity prevents enterolith formation. (Center for Equine Health) (Equus Magazine)

So I would not make vinegar the main plan.

The main plan is diet, forage balance, turnout, exercise, avoiding foreign material, and taking colic seriously.

Vinegar is not a force field. It is vinegar.

Common Mistakes Owners Make

Assuming All Colic Is Gas

Repeated colic deserves investigation. Enteroliths can cause intermittent obstruction before a severe blockage occurs.

Feeding Mostly Alfalfa to an At-Risk Horse

Alfalfa can be useful, but high-alfalfa diets are strongly associated with enterolith risk in certain populations. (ScienceDirect)

Waiting Too Long During Severe Colic

An obstructing enterolith can damage the bowel. Severe or recurring pain needs urgent veterinary assessment.

Feeding on Dirty or Sandy Ground

Ground feeding can increase ingestion of sand, stones, and debris. It also increases the chance of foreign material becoming part of the problem.

Treating Vinegar as the Whole Prevention Plan

Apple cider vinegar may slightly acidify the gut, but it has not been proven to reliably prevent enteroliths. (Equus Magazine)

Forgetting Post-Surgery Diet Changes

Recurrence is much more likely if recommended diet changes are not followed after surgery. UC Davis advises horses that have had enterolith surgery should not have alfalfa in their diets. (Center for Equine Health)

How To Prevent Enteroliths Long Term

You cannot remove every risk, but you can reduce the main ones.

A practical prevention plan includes:

• Keep alfalfa under 50% of the diet in at-risk horses

• Avoid alfalfa completely after enterolith surgery unless your surgical team gives different advice

• Feed more grass hay or appropriate pasture

• Provide daily turnout where possible

• Encourage consistent exercise

• Feed smaller, more frequent meals

• Avoid unnecessary bran and mineral-heavy feeds

• Keep feed away from sand, rocks, wire, twine, and debris

• Use mats, feeders, or clean feeding surfaces

• Provide clean water at all times

• Maintain a consistent feeding routine

• Review the diet with your vet after any recurrent colic

• Consider radiographs in high-risk horses with repeated colic

• Follow post-operative diet instructions carefully

AAEP’s general colic prevention guidance also supports feeding primarily roughage, avoiding excessive grain and energy-dense supplements, providing daily exercise or turnout, fresh clean water, parasite control, and reducing stress during changes in environment or workload.

Good prevention is not glamorous. It is hay math, turnout, clean feeders, boring routines, and not pretending repeated colic is “probably nothing.”

Will My Horse Be Okay?

Many horses do very well if enteroliths are detected and treated before bowel damage occurs.

Very small enteroliths may pass in manure or remain asymptomatic. Larger enteroliths can cause colic, obstruction, and in severe cases rupture. UC Davis notes that full recovery is very likely if resulting impactions are identified before damage to the colon occurs, and early surgical removal has a high success rate. (Center for Equine Health)

The outcome depends on:

• Stone size

• Stone location

• Whether there is partial or complete obstruction

• Whether bowel damage has occurred

• How quickly the horse receives surgery if needed

• Whether post-surgery diet changes are followed

• Whether the horse has recurrent stones

If your horse has had one mild colic episode and is now normal, the risk may be low.

If your horse has repeated colics, eats mostly alfalfa, has little turnout, or has had stones before, the risk is much higher and prevention should be taken seriously.

FAQs

Can enteroliths pass on their own?

Small enteroliths may pass in manure or remain unnoticed. Larger stones can obstruct the intestine and usually require surgery if they cause colic. UC Davis notes that very small enteroliths may remain asymptomatic and pass in manure, while larger stones can become dangerous. (Center for Equine Health)

Does alfalfa cause enteroliths?

Alfalfa does not guarantee enteroliths, but high-alfalfa diets are a major documented risk factor. A California study found that feeding 50% or more of the diet as alfalfa was significantly associated with enterolithiasis. (ScienceDirect)

Can apple cider vinegar prevent enteroliths?

Apple cider vinegar may slightly acidify gut contents, but it has not been proven to reliably prevent enterolith formation. It should not replace the core prevention plan of reducing alfalfa load, improving turnout, managing minerals, and investigating recurrent colic. (Equus Magazine)

How are enteroliths diagnosed?

Radiographs are often the best screening test, but they do not detect every case. Diagnosis may depend on horse size, stone location, feed contents in the bowel, equipment, and sometimes surgical exploration. (Center for Equine Health)

Is enterolith colic always surgical?

If an enterolith is causing colic from obstruction, surgical removal is the only successful treatment. Medical care may support the horse temporarily, but it does not remove a large obstructing stone. (Center for Equine Health)

Final Thoughts

Enteroliths are not the most common cause of colic everywhere, but when they occur, they can be serious.

The best prevention is not one magic supplement. It is risk reduction.

For at-risk horses, that means reducing high-alfalfa feeding, increasing grass hay or appropriate pasture, providing daily turnout and exercise, avoiding unnecessary bran and mineral-heavy feeds, keeping feed away from sand and foreign objects, and taking recurrent colic seriously.

The most important clinical clue is often the pattern.

One mild colic may be many things. Repeated colic in a high-risk horse should make enteroliths part of the conversation.

Do not wait for a full obstruction to take the risk seriously.

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If your horse has repeated colic, eats a high-alfalfa diet, has limited turnout, or has previously had enteroliths, ASK A VET™ can help you work through the risk factors and decide what needs veterinary attention before another colic episode becomes a crisis.