Insulin Dysregulation and Equine Metabolic Syndrome
Spring and autumn are beautiful times of the year—but for many horse owners they can also be the most worrying.
As lush pasture begins to grow, horses and ponies with Equine Metabolic Syndrome (EMS) or Insulin Dysregulation (ID) are at a much greater risk of developing laminitis.
Understanding why this happens is the first step in preventing it.
What Is Insulin?
Insulin is a hormone produced by the pancreas.
Whenever your horse eats feeds containing sugars or starches, these carbohydrates are broken down during digestion into glucose, which enters the bloodstream.
Insulin’s job is to move that glucose from the blood into the body’s cells, where it can be used as energy or stored for later use.
Think of insulin as a key.
The key unlocks the cell so glucose can enter.
What Happens in Insulin Dysregulation?
In horses with insulin dysregulation, the body’s tissues become less responsive to insulin.
Imagine trying to unlock a door with a key that no longer works properly.
The pancreas responds by producing more insulin in an attempt to move glucose into the cells.
This results in:
- Higher than normal insulin concentrations (hyperinsulinaemia)
- Insulin remaining elevated for longer after eating
- Increased risk of laminitis
Unlike diabetes in people, many horses with insulin dysregulation continue to maintain relatively normal blood glucose concentrations because their pancreas produces large amounts of insulin to compensate.
The problem is the excess insulin itself.
What Is Equine Metabolic Syndrome?
Equine Metabolic Syndrome (EMS) is a hormonal disorder characterised by:
- Insulin dysregulation
- Easy weight gain or obesity
- Regional fat deposits
- Increased susceptibility to laminitis
Common fat deposits may develop:
- Along the crest of the neck
- Around the tailhead
- Behind the shoulders
- Around the sheath or mammary glands
- Above the eyes
It is important to remember that not every horse with EMS is overweight.
Some horses appear to be an ideal body weight while still having significant insulin dysregulation.
What About Leptin?
Leptin is another hormone produced by fat tissue.
Normally, leptin tells the brain that the body has stored enough energy and helps reduce appetite.
In many overweight horses, leptin resistance develops.
This means the brain no longer responds normally to leptin, so the horse continues to feel hungry despite having adequate or excessive body fat.
Leptin resistance often occurs alongside insulin dysregulation and contributes to obesity.
Why Does Insulin Cause Laminitis?
Equine research shows that high insulin concentrations may trigger laminitis.
Unlike laminitis caused by severe illness or grain overload, endocrinopathic laminitis is not primarily an inflammatory disease.
Instead, prolonged elevations in insulin appear to alter the function of the laminae—the specialised tissues that suspend the coffin bone within the hoof.
If this damage continues, the laminae weaken and the coffin bone may rotate or sink, resulting in one of the most painful conditions affecting horses.
Which Horses Are Most at Risk?
Horses at greatest risk include:
- Ponies
- Easy keepers
- Native breeds
- Overweight horses
- Horses with PPID (Cushing’s disease)
- Horses with a previous history of laminitis
Periods of rapid pasture growth during spring and autumn are particularly high risk because young pasture often contains increased concentrations of water-soluble carbohydrates.
Feeding a Horse with Insulin Dysregulation
Nutrition is one of the most important tools for managing insulin dysregulation.
The goal is simple:
Reduce insulin responses while still providing a balanced diet.
Choose Low Sugar and Low Starch Feeds
Many equine nutritionists recommend a combined ESC + starch value below 10% for horses with insulin dysregulation or a history of laminitis.
Where only NSC values are available, aim for a forage with an NSC below approximately 10–12%, recognising that ESC and starch provide more useful information where possible.
Manage Pasture Carefully
During periods of rapid pasture growth:
- Restrict grazing where necessary.
- Use a grazing muzzle if appropriate.
- Provide low-sugar hay.
- Avoid unrestricted access to lush pasture.
Balance the Diet
Restricting pasture does not remove the horse’s requirement for vitamins and minerals.
A balanced diet should continue to provide:
- Copper
- Zinc
- Selenium (where required)
- Iodine
- Sodium
- Protein
- Essential amino acids
These nutrients remain essential for hoof health, immune function and normal metabolism.
Support the Hindgut
Healthy hindgut microbes help maintain digestive health.
Provide:
- Plenty of good-quality forage
- Gradual dietary changes
- Appropriate fibre sources
- Fresh, clean water at all times
Avoid large grain meals that may increase starch flow into the hindgut.
Should You Feed Magnesium or Chromium?
Magnesium and chromium are commonly marketed for horses with insulin dysregulation.
However, supplementation should only be considered if there is evidence the diet is deficient or if recommended by your veterinarian or equine nutritionist.
Current research of insulin dysregulation has shown that chromium may improve insulin sensitvity and stabilize blood glucose.
A balanced diet is far more important than relying on individual supplements.
Insulin Dysregulation in a Nutshell
- Insulin is a hormone produced by the pancreas.
- It helps move glucose from the bloodstream into body tissues.
- Horses with insulin dysregulation produce excessive amounts of insulin after eating.
- Persistently high insulin concentrations are the primary trigger for endocrinopathic laminitis.
- Horses with Equine Metabolic Syndrome are at significantly increased risk.
- Managing dietary sugar and starch is essential.
- Maintaining a healthy body weight dramatically reduces laminitis risk.
- Every horse should receive a balanced diet that meets vitamin, mineral and protein requirements.
The Bottom Line
Insulin dysregulation is one of the leading causes of laminitis in modern horses, yet it is also one of the conditions we can often manage successfully through good nutrition and careful management.
Understanding your horse’s individual risk, analysing forage where possible, controlling sugar and starch intake, maintaining a healthy body condition and feeding a balanced diet can dramatically reduce the risk of future laminitis episodes.
Every horse is different. The best feeding programme is one that is designed specifically for your horse, your pasture and your management system.
Nutrition is the science of prevention.
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