Diagnosing the Cause

Key Message

Laminitis is not the diagnosis, it is the result of an underlying problem.

Finding out why the horse developed laminitis matters because the management is different depending on the cause. Most cases are associated with high insulin, usually linked with Equine Metabolic Syndrome, PPID, or both, but other causes such as grain overload, retained placenta, serious systemic illness or supporting limb laminitis need a very different approach. This lesson is an overview of the questions and tests commonly used to investigate the cause. It is not intended to replace veterinary diagnosis.

At a Glance

• Most laminitis cases are associated with hyperinsulinaemia, or high insulin.
• The two main endocrine conditions to investigate are EMS and PPID.
• EMS and PPID are different conditions, but a horse can have both.
• Insulin and glucose are commonly tested together when EMS or high insulin is suspected.
• ACTH is commonly used when PPID is suspected.
• Horses should generally not be fasted before routine insulin or ACTH testing under the ECIR approach.
• Exercise, transport, stress, pain, illness, sample handling, season and laboratory method can all influence results.
• A single blood result should be interpreted alongside the horse’s history, clinical signs and management.
• Early PPID can sometimes be difficult to identify, and repeat or additional testing may be needed.
• If grain overload, retained placenta, severe illness or supporting limb laminitis is suspected, the situation needs to be approached differently and urgently.

The Full Lesson

Why does the cause matter?

Treatment should be guided by the underlying cause. A horse with PPID may require medication, while a horse with EMS needs a strong focus on diet and, once the feet are safe, exercise. A horse that develops laminitis after a retained placenta or grain overload needs a completely different type of emergency treatment.

This is why ECIR places Diagnosis first in its DDT+E approach, Diagnosis, Diet, Trim and Exercise. Their central principle is simple: successful management begins with knowing what you are actually dealing with.

Start with the history

Blood tests are important, but they are only one part of the picture.

A useful investigation starts with the horse’s history. Questions that may help point towards the cause include:

• Has the horse had laminitis before?
• Did the episode follow increased pasture access or a change in feed?
• Is the horse an easy keeper, cresty or carrying unusual fat deposits?
• Is the horse older or showing possible signs of PPID?
• Has there been a sudden feed room break in or grain overload?
• Has the horse recently been seriously ill?
• Has a mare recently foaled and possibly retained her placenta?
• Is the horse severely lame or unable to bear weight on another limb?
• Has there been any recent transport, strenuous exercise, medication or significant stress?

The pattern matters because laminitis associated with high insulin often looks very different from a horse that has become systemically ill after a grain overload or retained placenta.

The most common question, is insulin too high?

Current ECIR material places hyperinsulinaemia at the centre of most naturally occurring laminitis. The 2025 NO Laminitis! proceedings estimate that high insulin is involved in around 80 to 90 per cent of cases.

For that reason, insulin testing is one of the most useful investigations in a horse with unexplained or pasture associated laminitis.

Insulin and glucose

ECIR commonly recommends measuring insulin and glucose from the same blood sample when investigating EMS.

Glucose on its own is usually not enough to tell us whether a horse has EMS. Many horses can maintain a normal blood glucose while producing excessive amounts of insulin.

Why ECIR does not recommend fasting

ECIR recommends that horses are not routinely fasted before basal insulin and ACTH testing. Fasting can artificially lower insulin and may make an abnormal horse appear more normal than it really is. Instead, ECIR recommends testing under controlled, known feeding conditions, commonly with access to appropriate low HC hay rather than grain or a high carbohydrate meal.

The aim is to get a result that reflects the horse’s real metabolic state rather than an artificially low fasting value.

What about dynamic insulin tests?

Sometimes a resting insulin result does not give a clear answer.

In those cases, veterinarians may use a dynamic test, where the horse is given a measured sugar or carbohydrate challenge and insulin is measured afterwards.
These tests can help reveal an exaggerated insulin response that might not be obvious from a single resting sample.

The exact choice of test, dose, timing and interpretation is more technical and is best discussed with the veterinarian performing the test.

For this lesson, the important point is simply:

A normal resting insulin does not always completely rule out abnormal insulin responses.
Investigating PPID

PPID becomes increasingly important as horses age, although early disease can occur before the classic long coat develops.

The main blood test used to investigate PPID is ACTH.

A basal ACTH test requires a single blood sample and is widely used as the first line test for PPID.

However, ACTH needs to be interpreted in context.

ACTH changes with the season

ACTH naturally rises during late summer and autumn in all horses, with a much more pronounced rise in many PPID horses.

This used to make autumn testing difficult, but seasonally adjusted reference ranges are now available and can improve diagnostic accuracy throughout the year.

For Australian horses, remember that the seasonal pattern is six months opposite to the northern hemisphere material.

The important point is not to compare every ACTH result with one fixed number.

The time of year matters.

Other things can affect ACTH

The 2025 proceedings from Jo Ireland emphasise that ACTH can also be influenced by:
• Exercise
• Transport
• Stress
• Severe illness
• Pain
• Restraint
• Medication
• Breed
• Sample handling
• The particular laboratory assay being used

This means an ACTH result should not be interpreted in isolation.

Ideally, the horse is tested in a calm environment, not immediately after transport or strenuous work, and samples are handled according to the laboratory’s requirements.

What if ACTH is normal but PPID is still suspected?

Early PPID can be difficult to identify.

Dr Eleanor Kellon’s 2025 presentation on early PPID describes horses where clinical signs appeared before ACTH consistently tested above diagnostic thresholds.

If the history strongly suggests PPID but basal ACTH is normal or equivocal, a veterinarian may recommend repeat testing or a TRH stimulation test.

TRH testing can be more sensitive in some early cases, but it is also influenced by season and other factors, so timing and interpretation matter.

This is a good example of why the whole horse matters more than one laboratory number.

EMS and PPID can occur together

A horse can have EMS without PPID.
A horse can have PPID without high insulin.
And a horse can have both.

This is why testing only ACTH or only insulin may not always give the full picture. ECIR specifically describes PPID and EMS as separate conditions with overlapping signs that require careful diagnosis.

For an older horse with laminitis, it can therefore be useful to consider both ACTH and insulin rather than assuming one excludes the other.

What about non endocrine causes?

Not every laminitis case is metabolic. A horse that breaks into a feed room and consumes a large quantity of grain can develop severe hindgut disturbance and systemic inflammatory laminitis.

This is different from the high insulin pathway seen in most pasture associated laminitis.
Retained placenta and serious systemic illness

Laminitis can also develop secondary to severe illness, such as retained placenta, colitis, peritonitis, septicaemia or serious complications following surgery.

These horses are often systemically unwell as well as footsore.

Supporting limb laminitis

If a horse cannot bear normal weight on one limb because of a serious injury, the opposite limb may develop laminitis from prolonged excessive loading.

These situations need a different diagnostic and treatment approach from EMS or PPID.

What about radiographs?

Radiographs do not tell you why the horse developed laminitis, but they are an important part of understanding what has happened inside the feet.

They can show the relationship between the pedal bone and the hoof capsule, help assess rotation or sinking, and guide trimming and hoof support.

For that reason, diagnosis of the cause and assessment of the hoof damage really run alongside one another.

We cover that in more detail in Why Radiographs Matter.

A note on laboratory reference ranges

One of the more confusing things for owners is hearing that a blood result is “within the laboratory range” while another source considers it concerning.
Reference ranges depend on:
• The test used
• Whether the horse was fed or fasted
• The laboratory assay
• The population used to create the reference range
• The time of year
• The clinical situation

This is another reason results should be interpreted as part of the whole case rather than relying on one number in isolation.

What should the owner’s role be?

You do not need to become your horse’s veterinarian.
But you can become an informed member of the team.

It is reasonable to understand:
• Which condition is being investigated
• Which tests are being performed
• Whether the horse should be fasted or fed beforehand
• Whether transport, exercise or pain may influence the result
• How the sample needs to be handled
• Whether seasonal reference ranges are being used for ACTH
• Whether both EMS and PPID have been considered where appropriate
• What the diagnosis means for management

That knowledge helps you have a more useful conversation with your veterinarian without trying to interpret complex laboratory results on your own.

The Most Important Thing to Remember

Laminitis is the symptom.
The next question is:
Why did it happen?

For most horses, investigating high insulin and considering EMS and PPID is an important starting point.

But the history still matters. Grain overload, retained placenta, serious systemic disease and supporting limb overload can all cause laminitis through very different pathways.

The goal is to identify the most likely underlying cause so that the management plan actually addresses the problem.