Equine Metabolic Syndrome

Equine Metabolic Syndrome (EMS)

Equine Metabolic Syndrome (EMS) is a common condition in horses and ponies that affects how their bodies handle insulin. The main feature of EMS is insulin dysregulation, where the body overproduces insulin or doesn’t respond to it properly. This puts horses at a much higher risk for laminitis, a painful hoof disease.

Other signs of EMS may include obesity (especially fat deposits on the neck or tailhead), lethargy, and a tendency to gain weight easily. EMS is usually managed through diet changes, weight control, and regular exercise to help improve insulin sensitivity and reduce the risk of laminitis.

Equine Metabolic Syndrome (EMS) and Diabetes – What’s the connection?

EMS in horses is similar in some ways to Type 2 diabetes in people. In both cases, the body has problems using insulin, the hormone that helps control blood sugar levels.

• In people with Type 2 diabetes, the body either doesn’t make enough insulin or doesn’t respond to it properly. This leads to high blood sugar, which can cause serious health issues over time.
  
• In horses with EMS, the body becomes less sensitive to insulin (called insulin dysregulation). This causes the horse’s body to release more insulin than normal, which can lead to laminitis, a painful hoof condition.

Similarities between EMS and Type 2 Diabetes:

• Both involve insulin resistance (the body not responding well to insulin).
• Both are often linked to being overweight.
• Both require diet and lifestyle changes to manage.
• Both can lead to serious health problems if not treated early.

While EMS isn’t exactly the same as diabetes, understanding diabetes in people can help horse owners better manage EMS in their animals.

Commonality of EMS

While precise global prevalence rates are not well-documented on EMS, available studies provide insight into its occurrence in various regions:​

• United Kingdom: Research indicates that over 30% of horses are overweight or obese, conditions closely linked to EMS (Manfredi, J et al 2023).
  
• Canada: Similar to the UK, studies have found that over 30% of horses are overweight or obese, suggesting a significant at-risk population for EMS (Manfredi, J et al 2023). ​
  
• United States: The prevalence of equine obesity, a major risk factor for EMS, is reported to be between 19% and 40% in domesticated horse populations Morgan R et al (2015).
  

These figures highlight that a substantial portion of the equine population in these regions is at risk for developing EMS. However, comprehensive data from other global regions are limited, underscoring the need for further research to accurately determine EMS prevalence worldwide.

Hoof structure/laminitis video

Copyright Bova UK

Insulin is a hormone made by the pancreas. Its main job is to help move sugar (glucose) from the bloodstream into the body’s cells, where it’s used for energy.

After a horse eats, sugar levels in the blood rise. In response, the body releases insulin to help control those sugar levels. It’s like a key that unlocks the cell doors, allowing sugar to go in and be used or stored.

Keeping insulin levels in balance is key to maintaining a healthy horse!

What is Insulin dysregulation?

Insulin dysregulation means the horse’s body isn’t handling insulin and blood sugar (glucose) properly. This can happen in a few different ways:

• The horse may have high insulin levels even when resting.
• Insulin may spike too high after eating or after a sugar test.
• The horse’s body may not respond well to insulin, a condition known as insulin resistance.

High insulin levels (called hyperinsulinemia) usually happen when the pancreas makes too much insulin. This can be caused by:

• Eating feeds high in sugar and starch (non-structural carbohydrates or NSC)
• Certain gut hormones that tell the body to release more insulin after eating

Sometimes, the liver doesn’t clear out insulin from the blood fast enough, which can also lead to high insulin levels.

Insulin resistance means the horse’s tissues (like muscles and fat) don’t react the way they should to insulin. So, the body makes even more insulin to try to keep blood sugar in balance.

Hyperinsulinemia-Associated Laminitis (HAL) is the most common type of laminitis in horses and ponies—seen in over 90% of cases. It has replaced older terms like pasture-associated laminitis and endocrine-related laminitis.

HAL can develop slowly and may not be obvious at first. Over time, it often becomes a long-term issue, with repeated bouts of mild to severe lameness. It starts with damage and stretching in the sensitive tissues inside the hoof (called the digital lamellae), caused by high insulin levels in the blood (hyperinsulinemia). This early damage might not be noticed right away, but it usually leads to clear signs of laminitis later on.

HAL is different from other types of laminitis, such as those caused by infections (sepsis) or from putting too much weight on one leg (supporting-limb laminitis).

The exact cause of HAL is still being studied, but it seems to involve insulin mistakenly triggering certain cell receptors (called IGF-1 receptors) in the hoof, which may lead to tissue damage.

Breeds/ Age/demographic affected

Signs of EMS

Obesity and its link to Equine Metabolic Syndrome (EMS)

Obesity, whether it’s general (overall body fat) or regional (fat deposits in certain areas like the neck or tailhead), can make insulin dysregulation (ID) worse, which is a key part of Equine Metabolic Syndrome (EMS). However, research has shown that the connection between obesity and ID isn’t always consistent.

This means that not all obese horses have EMS, and not all horses with EMS are obese. Because of this, it’s important to test for insulin problems even in horses that look to be a healthy weight—especially if they’re at risk for laminitis or show other signs of EMS.

In short: obesity can raise the risk, but it’s not the only sign of EMS. Regular monitoring and early testing are key to managing this condition effectively.

1. Diagnosis- Karo test/blood test
2. Management
   1. Diet
   2. Exercise
   3. Forage
   4. Feeding
   5. Games/field management (Tamzin webinar)

Advice specific for donkeys is available from The Donkey Sanctuary.

---

References: 

• Morgan R, Keen J, McGowan C. Equine metabolic syndrome. Vet Rec. 2015 Aug 15;177(7):173-9. doi: 10.1136/vr.103226. PMID: 26273009; PMCID: PMC4552932.
• Manfredi, J. M., Jacob, S., & Norton, E. (2023). A one-health lens offers new perspectives on the importance of endocrine disorders in the equine athlete. Journal of the American Veterinary Medical Association, 261(2), 153-164. Retrieved Mar 21, 2025, from https://doi.org/10.2460/javma.22.11.0485
• Recommendations for the diagnosis and management of Equine Metabolic Syndrome (EMS) and Insulin Dysregulation, 2024. Available online: Equine Endocrinology Group [accessed 21/03/2025]