A new review article provides an up-to-date overview of equine metabolic syndrome (EMS), a common endocrine disorder that significantly increases the risk of hyperinsulinaemia-associated laminitis (HAL), now recognised as the most common and clinically important form of laminitis.
The review, by F. R. Bertin, brings together current understanding of how EMS develops, how it should be diagnosed, and the most effective ways to manage affected horses and ponies.
Why EMS matters?
At the centre of EMS is insulin dysregulation, the key abnormality that drives laminitis risk. This can involve high insulin concentrations at rest, an exaggerated insulin response after feeding, or reduced tissue sensitivity to insulin.
This matters because prolonged hyperinsulinaemia can directly trigger laminitis. The review reinforces how closely linked EMS and laminitis are, and why identifying horses at risk before a first clinical episode is so important.
It is not just a disease of obesity
Although EMS is commonly associated with obesity, the review makes clear that obesity alone is not enough for diagnosis.
Many horses with EMS are overweight or have regional fat deposits, such as a cresty neck, fat around the tail head, or mammary and preputial fat accumulation. However, some affected horses are lean, while not all obese horses have EMS. For that reason, body condition should not be used as the sole basis for diagnosis.
The key point is that EMS must be identified through appropriate metabolic testing, rather than appearance alone.
What drives EMS?
The review highlights environmental and management factors as the main drivers of EMS development.
The most important include:
- diets high in non-structural carbohydrates (NSC)
- unrestricted or poorly controlled pasture access
- physical inactivity
- obesity, particularly regional adiposity
- increasing age
- breed predisposition
Ponies and certain breeds, including native pony breeds, Arabians, Andalusians and Morgans, appear to be at greater risk than others.
Why insulin dysregulation is so important?
Insulin dysregulation is the defining feature of EMS and the best predictor of laminitis risk. According to the review, excessive dietary sugars and starches, altered insulin clearance by the liver, and impaired insulin signalling all contribute to sustained hyperinsulinaemia.
This means horses may have normal blood glucose concentrations while still experiencing harmful insulin abnormalities. That is one reason why EMS can be missed if clinicians rely only on obvious clinical signs or simple assumptions based on weight.
Diagnosis requires objective testing
One of the most useful messages in the review is that diagnosis should focus on identifying insulin dysregulation through testing.
Basal insulin measurement remains a practical starting point, but the review notes that it is specific rather than sensitive. In other words, a clearly elevated value is helpful, but a normal result does not rule out disease.
Dynamic testing is more informative. The oral sugar test is highlighted as one of the most reliable practical tools for detecting exaggerated postprandial insulin responses and assessing laminitis risk. Tests of insulin resistance, such as the insulin tolerance test, can provide additional information and may complement the diagnostic work-up.
Management starts with diet
The review emphasises that nutrition is the cornerstone of EMS management.
The primary aim is to reduce dietary NSC intake while still meeting the horse’s overall nutritional needs. Hay should generally form the basis of the diet, with total forage intake adjusted according to body condition and weight-loss goals. Where hay NSC content is unknown, soaking may help reduce soluble sugars.
Pasture access must also be carefully controlled, especially in horses and ponies at high risk of HAL. In many cases, initial removal from pasture is recommended, with any return to grazing managed cautiously and strategically.
High-starch and high-sugar concentrates should be avoided, and forage-based diets may need to be balanced with an appropriate low-NSC vitamin and mineral supplement.
Exercise and hoof care remain essential
Exercise plays an important role in improving insulin sensitivity and supporting weight loss, although its use must be guided by the horse’s laminitic status.
For horses without active laminitis, structured exercise can form an important part of management. However, horses with painful or unstable feet should not be exercised until they are comfortable and hoof stability has improved.
The review also stresses that hoof care is central to both acute and long-term management. Frequent farriery, regular radiographic assessment where needed, and close communication between veterinarian and farrier are all important components of successful care.
When medication may be needed
Although diet, exercise and foot care remain first-line measures, the review notes that medication may be appropriate in some cases, particularly when non-pharmaceutical management is not enough to control insulin dysregulation or when laminitis risk remains high.
Sodium-glucose cotransporter-2 (SGLT2) inhibitors are identified as a promising class of drugs, with emerging evidence that they can reduce insulin responses and support management of HAL. Other treatments, such as metformin and levothyroxine, may also have a role in selected cases, although their effects can be variable.
The review is clear that drug therapy should be individualised and used as an adjunct rather than a substitute for management changes.
Prognosis depends on early recognition
The overall prognosis for horses with EMS is favourable when the condition is recognised early and managed consistently. Horses diagnosed before laminitis develops have the best outlook.
Once hyperinsulinaemia-associated laminitis becomes recurrent or chronic, prognosis becomes more variable and depends largely on the degree of hoof damage and the success of long-term management. Relapse remains common if dietary control and monitoring are relaxed.
Why this review is useful?
This review is particularly valuable because it brings together the current evidence on a condition that is common, clinically important and often oversimplified.
It reinforces several key points: EMS is not simply a disease of fat horses, laminitis risk is closely tied to insulin dysregulation, and careful testing is essential for diagnosis. It also provides a practical framework for management, highlighting the importance of diet, pasture control, exercise, hoof care and, in selected cases, medication.
For owners, veterinarians and farriers, the message is clear: early detection and sustained, evidence-based management offer the best chance of protecting both metabolic health and long-term soundness.
