Researched by
Dr. Madison Ricard
Verified by
Dr. Jo Myers
Published on
Last updated on
5 min read

Key takeaways

Equine metabolic syndrome (EMS) occurs when insulin levels are consistently high, leading to dysfunction of the systems that regulate body fat and blood sugar.

  • EMS is caused by a combination of genetic predisposition and environmental factors, such as high-sugar diets and obesity, although it is unclear why some horses develop this condition and others do not
  • Horses with EMS are frequently obese, have cresty necks, and fat deposits in areas such as the tailhead and sheath
  • Affected horses are at risk of developing laminitis
  • Diagnosis involves physical examination, blood work, insulin response testing, and diagnostic imaging
  • Treatment focuses on weight loss and reducing sugar in the diet
  • When appropriately managed, EMS does not interfere with quality of life, and many horses continue to have athletic careers
  • Horses that develop laminitis have a poor prognosis for athletic pursuits
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A closer look: Equine Metabolic Syndrome

Insulin is the major hormone that regulates movement of blood sugar into cells. When insulin levels are high, cells no longer respond to insulin appropriately (insulin resistance). Horses with EMS have high insulin levels during fasting, release excessive insulin in response to sugar in the diet, and have cells that respond minimally to insulin.

The exact mechanism of EMS development is not clear, but is closely correlated with obesity. Left untreated, the condition can worsen and lead to more severe chronic illness, including laminitis, which can end an athletic career or even lead to euthanasia.

Risk factors

Equine metabolic syndrome is common in horses, particularly in “thrifty” breeds such as Arabians, Morgans, and ponies. Other risk factors for developing EMS include:

  • Offspring of mares or stallions with EMS
  • Obesity
  • High-sugar diet

Although the condition is not directly life-threatening, horses with EMS are susceptible to developing laminitis. Horses that are obese and have a “cresty” neck require prompt veterinary attention. Horses that develop signs of lameness, particularly a “sawhorse stance”, require immediate veterinary attention to reduce damage to the hoof structure.

In some cases, laminitic events may flare up or worsen suddenly, particularly in response to high-sugar diets such as spring pasture.

Possible causes

The exact cause for EMS is unknown, but a combination of genetic and environmental factors which predispose horses to developing high insulin levels in their bloodstream plays a role.

Main symptoms

The symptoms of EMS can be subtle, until a laminitic event occurs.

Founder lines occur when the growth rings in the hoof are wider at the heel than the toe.

Testing and diagnosis

Diagnosis of EMS begins with a physical examination to identify risk factors such as obesity and fat deposits. Further diagnosis involves:

  • Blood work
  • Insulin-level testing
  • Testing insulin response to sugar through administering a high-sugar feed
  • Diagnostic imaging

Steps to Recovery

The treatment of equine metabolic syndrome primarily focuses on weight loss and dietary changes. Management strategies include:

  • Removing grain from the diet and replacing with a ration balancer
  • Reducing the amount of hay fed to encourage weight loss
  • Feeding hay that is low in sugar
  • Reducing pasture access or using a grazing muzzle
  • Increasing exercise gradually, during periods where no lameness signs are noted

Some horses benefit from medications to help encourage weight loss or stabilize insulin levels.

Horses with EMS may require repeated blood testing to monitor their progress and control of the disease.

Equine metabolic syndrome is a lifelong condition; however, it can be managed successfully. Many EMS horses that receive appropriate management live long, healthy lives, and can maintain an athletic career. Horses that develop laminitis from inadequate management may become permanently lame or require early retirement from athletic tasks. Some horses with severe laminitis are euthanized due to poor prognosis.


Equine metabolic syndrome can be prevented through careful management of horses with identifiable risk factors. Most horses that develop EMS have a history of being an “easy keeper.” Prevention strategies are similar to treatment, and include preventing obesity, reducing sugar in the diet, and increasing exercise. Equine metabolic syndrome is not contagious.

Is Equine Metabolic Syndrome common?

Equine metabolic syndrome is common in horses, particularly “thrifty” breeds such as Arabians, Morgans, and ponies.

Typical Treatment

  • Weight loss
  • Dietary changes
  • Medication


Amy Young - Writing for UC Davis Veterinary Medicine Center for Equine Health
Janice E. Kritchevsky , VMD, DACVIM-LAIM, - Writing for Merck Veterinary Manual
Erica Larson - Writing for The Horse

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