Equine Metabolic Syndrome (EMS) is increasingly recognised as one of the most significant health challenges affecting Australia’s horse population. More than just a tendency to gain weight, EMS is a complex collection of metabolic and clinical abnormalities – of which insulin dysregulation is the most consistent and defining feature. As veterinarians, we are seeing the profound effects this condition can have on the long-term health, performance, and welfare of horses and ponies across all breeds.
What Is Insulin Dysregulation?
Insulin dysregulation describes the body’s inappropriate secretion of, or response to, insulin. In horses with EMS, this may involve one or more of the following:
- Resting hyperinsulinaemia – persistently elevated insulin levels even without recent feeding
- Post-prandial hyperinsulinaemia – an exaggerated insulin response after eating
- Insulin resistance – reduced sensitivity to insulin in tissues such as muscle, fat and liver
Other clinical features, such as general or regional obesity, elevated blood triglycerides, or high blood pressure, are often present but not always.
Understanding insulin’s role is key. When horses consume non-structural carbohydrates (NSC) – the sugars and starches found in grains, lush pasture, treats and some hays – are rapidly digested in the small intestine and absorbed as glucose. More glucose in the bloodstream triggers more insulin release.
In metabolic horses, this insulin response becomes disproportionately high, putting them at risk of serious complications.
Why EMS Matters: The Link to Laminitis
The most significant and potentially devastating consequence of uncontrolled EMS is laminitis. In fact, hyperinsulinaemia-associated laminitis (HAL) – previously termed “pasture-associated laminitis” – accounts for over 90% of laminitis cases in the general horse and pony population.
Although the exact mechanism continues to be studied, current evidence suggests that excessively high insulin levels inappropriately activate insulin-like growth factor-1 receptors (IGF-1R) in the lamellae of the hoof. This abnormal stimulation leads to structural weakening and separation within the hoof capsule.
For affected horses, success hinges on simultaneously addressing metabolic dysfunction alongside therapeutic farriery and pain management.
EMS and obesity frequently occur together. Obesity worsens insulin resistance, which then promotes further fat accumulation – a cycle that increases the risk not only of laminitis but also osteoarthritis, soft-tissue injuries, and colic.
Risk Factors and Early Warning Signs
Although EMS is most commonly diagnosed in middle-aged horses, it can occur at any age. Certain breeds – ponies, Arabians and Warmbloods – are over-represented, and genetics appear to play a role. However, environmental factors remain the strongest contributors, particularly:
- Diets high in NSC (unrestricted pasture, grain-based feeds, excessive treats)
- Lack of regular exercise
- Obesity or regional fat deposits (notably along the crest of the neck)
Neck crest enlargement is particularly important, as studies have shown a negative correlation between neck circumference and insulin sensitivity.
EMS may also occur alongside Pars Pituitary Intermedia Dysfunction (PPID), or “Equine Cushing’s Disease”, further complicating diagnosis and management.
Common signs include:
- Laminitis (acute or chronic)
- Generalised or regional obesity
- Fat pads along the crest, rump, or shoulders
- Difficult or “easy keeper” weight gain
How We Diagnose EMS
Diagnosis begins with a combination of clinical assessment and endocrine testing.
- Basal Insulin Testing
A single blood sample taken in the fed state.
A high result confirms EMS; however, a normal value does not rule it out.
- Dynamic Testing
Dynamic tests evaluate the horse’s insulin response to a known sugar load.
The most commonly used is the Oral Sugar Test (OST), where the horse is fasted for 3–6 hours before administration of corn syrup or glucose powder. Blood samples taken before and after provide a clear picture of insulin responsiveness.
Management and Prevention: What Owners Can Do
The most effective treatment for EMS remains diet and management, and consistent and appropriate farriery/hoof care—areas where owner commitment makes an enormous difference.
Dietary Strategies
- Limit or remove access to pasture, especially during times of high sugar accumulation (cool, sunny days; early spring). When pasture access is important for welfare, grazing in shaded areas for short periods – ideally early morning -can be safer.
- Using grazing muzzles can help, though many determined horses become adept at removing them.
- Offer low-NSC hay (<10%), such as tested Teff or Rhodes grass hay.
- Soak Lucerne hay for 1 hour in cold water to reduce soluble sugars.
- Avoid all grains, pellets high in starch, and treats.
- Use slow feeders or divide hay into multiple small meals to minimise insulin spikes.
For weight reduction, feed approximately 1.5% of bodyweight (dry matter) per day. For a 400 kg horse, this equates to ~7 kg hay daily.
Exercise
Where no laminitis is present, controlled exercise improves insulin sensitivity and supports healthy weight loss.
Underweight Horses With EMS
Not all EMS horses are overweight. For those with concurrent laminitis but normal or low body condition, the goal shifts to maintaining condition while reducing NSC intake. Oils may be used to increase caloric density safely.
Medication Options
While management remains the cornerstone of treatment, certain horses may require medication:
- SGLT2 inhibitors (e.g., ertugliflozin) reduce glucose reabsorption in the kidneys, thereby decreasing blood glucose and insulin.
- Metformin and thyroxine may have limited or specific roles but are not routinely relied upon.
The Bottom Line
EMS is a manageable condition, but it requires informed, consistent effort from owners and veterinarians. Diet, environment, and early detection remain the most powerful tools we have to prevent irreversible damage and protect horses from laminitis.
If you suspect your horse may be at risk of EMS or require guidance on testing and management, seek assistance from your local veterinarian.
Written by Lucy Cudmore & Dr Matthew Kelly