Equine Metabolic Syndrome

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

A Closer Look: What is EMS in Horses?

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. 

Symptoms of laminitis include:

• Mild lameness that worsens over time

• “Founder lines” and a dished appearance to the hoof wall due to an excessively long toe

• Increased time laying down

• “Sawhorse stance”, where the horse rocks backwards onto the hind limbs with the front feet extended forwards

Exercise intolerance

Limited mobility

Ring sour/poor performance

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. Symptoms include: 

• Cresty neck

• Fat deposits around the tail head, in the sheath, or above the eyes

• “Founder lines” in the hooves, where the growth rings 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 life-long 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 EMS Common in Horses?

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

Typical Treatment

• Weight loss

• Dietary changes

• Medication

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