Lawsonia in Foals: Diarrhea, Edema and Treatment

By Dr Duncan Houston

Lawsonia can look like ordinary foal diarrhea at first, but the real danger is protein loss.

A weanling foal with diarrhea is always worth paying attention to. But when that diarrhea is paired with fever, weight loss, dullness, colic, or swelling under the belly, legs, jaw, or sheath, one disease should be high on the list: equine proliferative enteropathy, commonly called Lawsonia.

Lawsonia intracellularis damages the small intestine and causes a protein-losing enteropathy. That means the foal does not just have loose manure. The gut becomes thickened, absorption is impaired, and blood protein can drop dangerously low. That is why affected foals may develop edema, weakness, poor growth, and sometimes sudden deterioration.

The good news is that early treatment usually works very well. The bad news is that waiting too long can turn a very treatable disease into an intensive care case.

Quick Answer

Lawsonia in foals, also called equine proliferative enteropathy or EPE, is an intestinal disease caused by the intracellular bacterium Lawsonia intracellularis. It mainly affects weanling and yearling horses and can cause diarrhea, fever, weight loss, colic, depression, rough coat, low blood protein, and edema under the belly, limbs, head, or sheath.

A foal with diarrhea plus swelling, fever, weight loss, or dullness should be checked by a veterinarian urgently. Diagnosis usually involves blood protein testing, abdominal ultrasound, fecal PCR, and serology, and treatment usually requires targeted antimicrobials plus supportive care such as fluids, plasma, nutrition, and gastroprotectants in more serious cases. (Equine Disease Communication Center)

What Is Lawsonia in Foals?

Lawsonia intracellularis is an obligate intracellular bacterium, meaning it lives inside cells. In foals, it causes equine proliferative enteropathy, a disease where the intestinal lining becomes thickened and less able to absorb nutrients and protein properly. EDCC describes EPE as an enteric disease that causes intestinal inflammation and thickening. (Equine Disease Communication Center)

The disease mainly affects young horses, especially weanlings. AAEP states that EPE is typically seen in weanling and yearling horses, with young horses between two and eight months most commonly represented in North America, although cases have been reported in adults.

The key clinical problem is not just diarrhea.

The real problem is loss of protein through a damaged gut.

When albumin and total protein drop, fluid leaks out of the bloodstream into tissues. That is why owners may notice swelling under the belly, around the legs, under the jaw, or around the sheath. MSD Veterinary Manual explains that hypoproteinemia and hypoalbuminemia lead to low plasma oncotic pressure and subsequent ventral edema. (MSD Veterinary Manual)

Why Lawsonia Is Easy To Miss Early

Early Lawsonia can look vague.

A foal may simply seem dull, growing poorly, or slightly off feed. Diarrhea may be mild at first. Some foals do not look dramatically sick until the protein loss is already advanced.

In practice, the cases that worry me most are not always the foals with the messiest diarrhea. They are the weanlings that are a little depressed, a little thin, a little swollen, and not gaining weight the way they should.

Those are the foals that need bloodwork before everyone waits another week.

AAEP notes that around 5% of exposed horses may develop clinical disease and another 5% may develop subclinical disease that shows as poor weight gain.

How Does Lawsonia Spread?

The exact reservoir is still not fully understood, but fecal-oral exposure is suspected. That means foals are thought to be exposed by ingesting contaminated fecal material from infected animals or contaminated environments. AAEP notes that wildlife, rodents, and feral or domesticated pigs may play a role, while University of Melbourne guidance notes that rodents appear to be a suitable reservoir host and that farms may see year-to-year variation depending on environmental and climatic factors.

Lawsonia can survive in the environment for a period of time. AAEP states that Lawsonia thrives in low oxygen environments such as feces and may remain infective at milder temperatures for up to two weeks.

That is why farm hygiene, feces removal, rodent control, and early isolation matter.

Not glamorous. Very useful. Horses rarely reward glamorous anyway.

Which Foals Are Most at Risk?

Lawsonia is mainly a disease of young horses, especially weanlings.

Higher risk situations include:

• Foals between two and eight months of age
• Weanlings and yearlings
• Recently weaned foals
• Farms with previous Lawsonia cases
• Farms with multiple foals or youngstock
• Foals with poor weight gain
• Foals in late summer, fall, or early winter in North America
• Foals exposed to contaminated feces, rodents, wildlife, or high traffic environments
• Foals under stress from weaning, transport, diet change, or group mixing

EDCC notes that North American cases are most commonly seen from August through January and that young horses between two and eight months are most commonly represented. (Equine Disease Communication Center)

The timing will vary by country, climate, farm system, and season, so farms with previous Lawsonia cases should work from their own pattern rather than assuming the disease only occurs in one calendar window.

What Are the Symptoms of Lawsonia in Foals?

Lawsonia signs can range from subtle to severe.

Common signs include:

• Diarrhea
• Soft manure or watery manure
• Fever
• Depression
• Reduced appetite
• Rapid weight loss
• Poor weight gain
• Rough coat
• Colic signs
• Lethargy
• Swelling under the belly
• Swelling of the legs
• Swelling under the jaw
• Swelling around the sheath or prepuce in colts
• Dehydration in more severe cases

AAEP lists anorexia, rapid weight loss, dependent edema, rough hair coat, fever, colic, diarrhea, and depression as clinical signs of EPE.

The most important combination is:

Weanling age plus diarrhea plus low protein or edema.

That combination should make Lawsonia a serious rule-out.

Why Does Lawsonia Cause Edema?

Edema happens because blood protein, especially albumin, becomes too low.

Albumin helps keep fluid inside the bloodstream. When albumin drops, fluid leaks into tissues. That is why the swelling often appears in dependent areas, such as the lower belly, legs, head, or sheath.

This is one of the clearest clues that the problem is more than simple loose manure.

EDCC describes hypoalbuminemia as a consistent finding across almost all EPE cases, always accompanied by hypoproteinemia. (Equine Disease Communication Center)

A practical owner checkpoint:

If a foal has diarrhea and visible swelling, do not manage it as a mild digestive upset. Call your vet.

Lawsonia Risk Framework

Risk level	What it looks like	What it may mean	What to do
Low risk	Bright foal, normal appetite, normal temperature, soft manure once, no swelling, gaining weight	Mild digestive upset or diet-related change possible	Monitor closely and check temperature
Moderate risk	Weanling with mild diarrhea, reduced appetite, rough coat, slower weight gain, or mild fever	Early Lawsonia or another foal disease possible	Call your vet and consider blood protein testing
High risk	Diarrhea plus fever, depression, colic, weight loss, or edema under belly, legs, jaw, or sheath	Lawsonia becomes a major concern	Veterinary assessment, bloodwork, ultrasound, PCR or serology
Critical	Severe depression, severe diarrhea, dehydration, marked edema, colic, weakness, abnormal bloodwork, rapid deterioration	Severe EPE, sepsis, necrotizing disease, or another serious illness possible	Urgent veterinary care or referral

The decision point is simple: diarrhea alone can be many things, but diarrhea plus edema in a weanling is a red flag.

When Is Lawsonia an Emergency?

Call a veterinarian urgently if a foal has:

• Diarrhea with fever
• Diarrhea with swelling under the belly, limbs, jaw, or sheath
• Depression or weakness
• Colic signs
• Rapid weight loss
• Poor appetite lasting more than 12 to 24 hours
• Dehydration
• Recumbency or inability to rise normally
• Very watery diarrhea
• Blood in manure
• Signs worsening over a few hours
• Multiple foals on the property becoming dull, thin, or diarrheic

AAEP notes that rare cases of EPE can involve rapid decompensation or death, often preceded by fever and bloodwork changes suggesting possible bacterial translocation across damaged intestinal mucosa.

That is why a dull, febrile, swollen weanling should not be watched for “one more day.”

How Do Vets Diagnose Lawsonia?

Lawsonia diagnosis usually combines the foal’s age, signs, bloodwork, ultrasound, and specific testing.

Bloodwork

Bloodwork is often the first major clue.

Vets look for:

• Low total protein
• Low albumin
• Evidence of dehydration
• White blood cell changes
• Fibrinogen or inflammatory marker changes
• Electrolyte abnormalities
• Kidney values if dehydration or severe disease is present

AAEP describes hypoalbuminemia, often severe, as a consistent finding in EPE, and notes that more severe CBC and chemistry changes can be associated with necrotizing EPE and sudden deterioration.

University of Melbourne guidance also recommends monitoring at-risk herd mates with total plasma protein because it is inexpensive and useful, with foals below 50 g/L needing further testing. (Faculty of Science)

Abdominal ultrasound

Ultrasound can identify thickened small intestine, which is one of the hallmark findings. AAEP states that thickening of the small intestinal wall is a hallmark of proliferative enteropathies caused by Lawsonia and that ultrasound may identify wall thickening greater than 5 mm. It also warns that the absence of thickening does not rule out EPE.

That last point matters.

A normal ultrasound does not fully eliminate Lawsonia if the age, signs, and low protein fit.

Fecal PCR

Fecal PCR detects Lawsonia DNA in manure and is widely used. AAEP calls fecal PCR the best antemortem diagnostic test for EPE, but false negatives are possible, especially after antimicrobial treatment has started or late in the disease course.

This is why collecting samples before starting treatment is ideal when the foal is stable enough.

Serology

Serology detects antibodies to Lawsonia. It can support the diagnosis, especially when fecal PCR is negative but the clinical picture fits. AAEP notes that paired serology seven to fourteen days apart is ideal, but many cases are treated before waiting because the clinical course can require fast action. Serology should support the diagnosis, not be used as the only test.

Herd screening

Once one foal is diagnosed on a farm with multiple weanlings, testing herd mates is often recommended. University of Melbourne guidance specifically recommends testing herd mates after diagnosis on a farm with multiple weanlings. (Faculty of Science)

What Else Can Look Like Lawsonia?

Not every foal with diarrhea has Lawsonia.

Important rule-outs include:

• Salmonellosis
• Clostridial diarrhea
• Potomac horse fever, where regionally relevant
• Rhodococcus equi associated disease
• Parasite burdens
• Equine coronavirus
• Rotavirus in younger foals
• Dietary change
• Sand enteropathy
• Gastric ulcers
• NSAID-associated intestinal injury
• Inflammatory or infiltrative bowel disease
• Sepsis
• Pneumonia with secondary gastrointestinal signs

MSD Veterinary Manual lists salmonellosis, clostridiosis, Neorickettsia risticii, Rhodococcus equi, parasitic infections, and infiltrative or inflammatory bowel disease among the differentials for EPE. (MSD Veterinary Manual)

This is the veterinary reasoning that matters: Lawsonia is a strong suspect when the pattern fits, but foal diarrhea has a big differential list.

Guessing wastes time.

Testing directs treatment.

How Is Lawsonia Treated?

Treatment usually has two parts:

1. Antimicrobials that can reach an intracellular organism

2. Supportive care to manage dehydration, protein loss, gut damage, and poor nutrition

Targeted antimicrobials

Because Lawsonia lives inside cells, the antimicrobial choice matters. AAEP lists tetracyclines such as oxytetracycline, doxycycline, and minocycline, or chloramphenicol, as commonly used antimicrobials. It also notes that antimicrobial choice should reflect the foal’s age and toxicity risk.

University of Melbourne guidance states that early cases can often be treated with oral doxycycline, while advanced disease may need intravenous oxytetracycline because gastrointestinal absorption may be reduced. (Faculty of Science)

This is not a disease where random leftover antibiotics are a good idea.

Wrong drug, wrong timing, or delayed treatment can cost the foal valuable time.

Why macrolides need caution

Macrolides can have activity against Lawsonia, but they are not casual drugs in older foals and adult horses. AAEP warns that macrolide use in older foals and adults is associated with increased risk of life-threatening colitis.

That is one of those clinical details owners do not need to memorise, but they do need to respect: do not medicate these foals without a veterinarian.

Supportive care

Supportive care may include:

• IV fluids
• Plasma transfusion
• Colloid support in selected cases
• Electrolyte correction
• Anti-ulcer medication
• Enteral nutrition
• Partial parenteral nutrition in severe cases
• Pain relief when appropriate
• Monitoring albumin, total protein, hydration, appetite, and weight

AAEP states that supportive care typically involves IV fluids and oncotic support such as plasma or colloids, with additional treatments potentially including anti-ulcer medication and enteral or parenteral nutrition.

Plasma is used because the foal is losing protein. But in severe cases, protein levels can remain low for some time even after treatment begins. University of Melbourne notes that plasma transfusions may produce frustratingly small increases in total plasma protein and that total plasma protein can remain low for long periods after clinical recovery. (Faculty of Science)

How Long Does Recovery Take?

Many foals improve clinically within days once the right treatment is started, but full recovery can take longer.

Appetite, attitude, manure quality, and weight gain may improve first. Albumin and total protein can take weeks to normalise. AAEP notes that the horse’s clinical and physical condition, and albumin normalisation, may take significantly longer and in some cases months to fully recover.

MSD Veterinary Manual reports that with treatment, around 90% of foals usually survive, and University of Melbourne guidance reports excellent prognosis with early treatment, with 93% of treated foals reported to fully recover, although severely affected cases can have much higher mortality. (MSD Veterinary Manual)

The practical takeaway:

Early cases are usually very treatable. Advanced cases can become expensive, intensive, and risky.

Is Lawsonia Contagious?

Lawsonia is considered transmissible, with fecal-oral exposure suspected. Affected foals may shed the organism in manure, and environmental contamination can matter. AAEP recommends isolating affected horses for seven days after starting treatment and promptly removing feces. It also recommends limiting wildlife and rodent exposure, especially in barns.

This does not mean panic every time one foal has soft manure.

It means that once Lawsonia is suspected, the farm should think in systems:

• Which foals are at risk?
• Who has low total protein?
• Who is losing weight?
• Who has fever?
• Where is manure accumulating?
• Are rodents or wildlife accessing feed or bedding?
• Are multiple foals sharing contaminated areas?

Good Lawsonia control is not just treating the sick foal. It is finding the next foal before they become sick.

What Should You Do Right Now?

If your foal has mild soft manure but is bright

Check temperature.

Monitor appetite, manure, attitude, hydration, and weight gain.

If signs settle quickly and the foal remains bright, this may be less urgent. But if the foal is in the Lawsonia age group or on a farm with a history of EPE, early blood protein testing is sensible.

If your foal has diarrhea and fever

Call your veterinarian.

Fever changes the urgency because it suggests more than simple diet change.

If your foal has diarrhea and swelling

Treat this as urgent.

Swelling under the belly, limbs, jaw, or sheath can indicate low albumin and protein loss.

If multiple foals are affected

Speak to your vet about farm-level testing.

Do not just treat one foal and ignore herd mates. University of Melbourne guidance recommends testing herd mates after a diagnosis on a farm with multiple weanlings. (Faculty of Science)

If treatment has started

Follow your vet’s monitoring plan.

Track:

• Temperature
• Appetite
• Manure consistency
• Attitude
• Weight
• Edema
• Hydration
• Albumin and total protein
• Ultrasound changes if rechecked

Do not stop medication early because the foal looks brighter after two days.

Common Mistakes With Lawsonia in Foals

Mistake 1: Waiting because the diarrhea is mild

Mild diarrhea can still be Lawsonia, especially if the foal is dull, febrile, losing weight, or low in protein.

Mistake 2: Missing edema

Swelling under the belly, limbs, jaw, or sheath is not just cosmetic. In a weanling with diarrhea, it can be a major low-protein warning sign.

Mistake 3: Treating with random antibiotics

Lawsonia is intracellular, so antimicrobial choice matters. AAEP lists tetracyclines or chloramphenicol as common choices and cautions that treatment choice should consider age and toxicity risk. (Equine Disease Communication Center)

Mistake 4: Assuming one negative PCR rules it out

Fecal PCR can be falsely negative, especially after treatment has started or late in disease. Serology and the clinical picture still matter.

Mistake 5: Forgetting herd mates

Subclinical disease can show as poor weight gain. Once one foal is confirmed, at-risk foals on the property should be monitored.

Mistake 6: Expecting albumin to normalise immediately

The foal may look better before protein levels fully recover. Albumin normalisation can take weeks or longer in some cases.

Mistake 7: Ignoring rodents and wildlife

The exact reservoir is not fully solved, but wildlife and rodents are suspected contributors. Farm hygiene and rodent control are practical prevention tools.

Can Lawsonia Be Prevented?

Prevention is not perfect, but risk can be reduced.

Useful farm strategies include:

• Monitor weanlings during the farm’s risk season
• Weigh or body condition score foals regularly
• Check total protein in at-risk foals
• Act early on poor weight gain
• Isolate sick foals
• Remove feces promptly
• Reduce manure build-up in foal areas
• Control rodents
• Limit wildlife access to feed and barns
• Clean shared equipment
• Avoid overcrowding
• Reduce weaning and transport stress where possible
• Keep accurate records of cases and timing
• Discuss off-label vaccination only with your veterinarian

University of Melbourne guidance recommends total plasma protein monitoring as an inexpensive way to monitor at-risk horses, while AAEP recommends isolation of affected horses, prompt feces removal, and limiting wildlife and rodent exposure. (Faculty of Science)

Is There a Vaccine for Lawsonia in Foals?

There is currently no licensed equine-specific Lawsonia vaccine.

Some farms use a swine Lawsonia vaccine off-label under veterinary supervision. AAEP notes that limited studies describe rectal administration of the porcine vaccine to foals, with vaccinated foals showing less severe disease and reduced pathogen shedding compared with unvaccinated foals, but this is off-label and veterinarians should check whether cross-species vaccine use is permitted under local rules.

UC Davis also notes that no vaccines are labelled for equine use and that a commercially available swine product has been studied for safety and efficacy in foals. (Equine Disease Research Lab)

This is not a do-it-yourself farm decision.

Off-label vaccination should be planned with a veterinarian who understands your region, farm history, legal rules, and foal risk.

Myth vs Reality

Myth	Reality
“Foal diarrhea is usually just diet change.”	Sometimes, but weanlings with fever, weight loss, edema, or low protein need Lawsonia testing.
“If there is no diarrhea, it cannot be Lawsonia.”	Some foals may show poor weight gain, edema, fever, or dullness before diarrhea is obvious.
“A negative fecal PCR rules it out.”	False negatives can occur, especially after antimicrobial treatment has started or late in disease.
“Plasma fixes the problem immediately.”	Plasma can support oncotic pressure, but protein levels may remain low for a long time after clinical improvement.
“Adult horses commonly get Lawsonia.”	Lawsonia is mainly a disease of weanlings and young horses, although adult cases have been reported.
“The vaccine is a standard horse vaccine.”	There is no licensed equine Lawsonia vaccine. Swine vaccine use is off-label and vet-directed.

Frequently Asked Questions

Can adult horses get Lawsonia?

Adult cases have been reported, but Lawsonia is mainly a disease of weanlings and young horses. AAEP states that young horses between two and eight months are most commonly represented, although adult cases have occurred.

Is Lawsonia contagious between foals?

Lawsonia is suspected to spread by fecal-oral exposure, and affected foals can shed the organism in feces. Isolation, manure removal, and monitoring of at-risk herd mates are important once the disease is suspected or confirmed.

What is the biggest warning sign of Lawsonia?

The most suspicious combination is a weanling with diarrhea, weight loss, fever, low blood protein, or edema under the belly, limbs, jaw, or sheath. EDCC notes that ventral edema, diarrhea, and hypoalbuminemia combined with the right age and season can be almost pathognomonic for EPE. (Equine Disease Communication Center)

How do vets confirm Lawsonia?

Vets usually combine bloodwork, abdominal ultrasound, fecal PCR, and serology. Bloodwork often shows low albumin and total protein, ultrasound may show thickened small intestine, fecal PCR detects Lawsonia DNA, and serology detects antibodies. (Equine Disease Communication Center)

Can foals recover from Lawsonia?

Yes. Prognosis is usually excellent with early treatment. University of Melbourne guidance reports 93% full recovery in treated foals, although severely affected cases can have higher mortality. (Faculty of Science)

The Bottom Line

Lawsonia is one of the most important diseases to think about in a weanling with diarrhea, poor growth, fever, weight loss, or swelling.

The key clue is protein loss.

A foal with mild loose manure but bright attitude may not be an emergency. A weanling with diarrhea, edema, fever, dullness, colic, or rapid weight loss is different. That foal needs a veterinarian, blood protein testing, and a proper Lawsonia workup.

Early treatment usually gives a very good outcome.

Late treatment can mean severe hypoproteinemia, dehydration, plasma transfusions, intensive care, prolonged recovery, and a much higher risk of complications.

If you manage foals, especially on a farm with previous Lawsonia cases, do not wait for the dramatic version. Track weight gain, watch for swelling, check temperatures, monitor total protein in at-risk foals, and call your vet early when the pattern fits.

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If you are unsure whether a foal’s diarrhea, poor growth, fever, or swelling could be Lawsonia, ASK A VET™ can help you organise the signs, track the timeline, and decide when veterinary care should not wait.