For many horse owners, receiving a diagnosis of Equine Metabolic Syndrome can feel overwhelming and confusing. Often, they may not fully understand the type of horse healthcare this condition entails.
This article will explain what Equine Metabolic Syndrome is, identify which horses are most at risk, and outline effective treatment options to help you care for your horse.
What is Equine Metabolic Syndrome?
Equine Metabolic Syndrome (EMS) is a metabolic disorder characterized by insulin dysregulation in horses. Horses with EMS don’t respond to insulin as well as they should. As a result, their bodies produce extra insulin, even though their blood sugar levels stay normal.
Although EMS often affects overweight horses, it can also occur in horses with other body conditions. The core problem in EMS is insulin dysregulation, which resembles—but is not identical to—the metabolic issues seen in humans with type 2 diabetes.
Typically, after a horse eats, the pancreas releases insulin to help the body’s tissues absorb glucose from the bloodstream. In horses with EMS, their bodies don’t respond correctly to insulin, so glucose remains in the blood. The pancreas compensates by producing more insulin, leading to consistently high insulin levels after meals and sometimes throughout the day.
Horses with EMS are at greater risk of laminitis, a painful inflammation that weakens the tissues connecting the hoof wall to the bone. Hormonal and metabolic imbalances and exceptionally high insulin levels worsen damage to the coffin bone and raise the chances of laminitis.
While EMS can also develop as a secondary condition to Pituitary Pars Intermedia Dysfunction (PPID or Cushing's Disease), not all horses with PPID develop EMS.
Common Signs of Equine Metabolic Syndrome
While each horse can present signs of EMS differently, some of the more common signs include:
Being Overweight: Horses with EMS, or those prone to it, are often, though not always, overweight. Even with weight-loss efforts, these horses may struggle to shed excess body weight due to underlying metabolic challenges.
Horses are considered overweight when their Body Condition Score (BCS) is 7 or higher on a 1–9 scale, while a score between 4 and 6 is considered ideal. To learn more about body condition and crest scoring, visit the Tribute Equine Nutrition Wellness System.
Fat Deposits (Regional Adiposity): Fat deposits in certain areas of the horse's body are stronger indicators of EMS and insulin resistance than general obesity alone.
This pattern of fat accumulation, known as regional adiposity, is a common sign of EMS and can appear even in horses that aren't visibly overweight. Commonly affected areas include the crest of the neck, shoulders, tailhead, and sometimes around the eyes, sheath, and mammary region.
Other Possible Signs: Some horses with EMS may also show signs such as increased thirst and urination, low energy or lethargy, and changes in reproductive function.
Diagnosing Equine Metabolic Syndrome
Diagnosing EMS requires a veterinarian’s evaluation and testing. Key diagnostic steps include:
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Physical Exam: Veterinarians record the BCS and neck circumference, then check the hooves for signs of laminitis, such as widened growth rings, a strong digital pulse, warmth, and changes in gait.
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Radiographs: Such as lateral images of the pedal bone to detect past laminitis damage, like coffin bone rotation or sinking.
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Blood Tests:
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Baseline Insulin & Glucose: High insulin levels (>20 uIU/mL) suggest insulin resistance, although mild cases can test normal. Fasting is no longer recommended, as it may lead to false negatives. The current best practice is to allow continuous access to forage (hay or pasture, no grain) before testing.
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Oral Sugar Test (OST): After feeding the horse corn syrup, insulin levels are measured at 60 and 90 minutes. Levels over 60 uIU/mL indicate abnormal insulin response.
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Intravenous Glucose Tolerance Test (IVGTT): The most sensitive test, measuring how quickly glucose and insulin levels return to normal after IV dextrose.
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Leptin and Adiponectin: These are hormones linked to fat and insulin sensitivity. Leptin is typically higher, while adiponectin is lower in EMS horses, which helps track metabolic status.
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PPID Testing: Since PPID can worsen insulin resistance, horses over 15 or with symptoms like excessive drinking or laminitis may be tested for PPID using ACTH or TRH stimulation tests.
Because mild EMS may not be detected on simple blood tests, dynamic tests such as OST or IVGTT are often necessary for an accurate diagnosis. Testing should ideally occur in low-stress conditions and avoid periods of active laminitis to prevent misleading results.
What Factors Can Exacerbate Equine Metabolic Syndrome?
EMS may be triggered and worsened by a combination of genetic, environmental, and nutritional factors, including:
Weight
As a horse becomes more overweight, its fat tissue also releases chemicals that cause inflammation, making it harder for the body to use insulin properly.
Age
Older horses and ponies are more likely to develop insulin resistance and EMS.
Breed
Although any horse can develop EMS, breeds like ponies, Warmbloods, and Quarter Horses are more prone due to genetics favoring efficient fat storage—a genetic survival trait that now often causes excessive weight gain. Any “easy keeper” prone to gaining weight is at risk, especially when environmental factors trigger the condition.
Diet, Nutrition, and Exercise
High-sugar diets combined with a lack of exercise increase a horse’s risk of being overweight and developing EMS. Diets high in non-structural carbohydrates (NSC), such as sugars and starches, increase blood glucose and insulin levels, particularly during rapid pasture growth in spring when grass sugar levels are higher.
A horse’s response to NSC depends on factors like individual differences, feed amount and rate, NSC percentage, and feed processing. A common mistake is horse owners focusing solely on the NSC percentage of feed without considering how much the horse consumes or the NSC content of the forage, both of which can exacerbate EMS symptoms if too high.
Other Health Conditions
Certain conditions—like untreated PPID—can trigger EMS in horses already at risk. PPID disrupts insulin regulation, increasing the risk of developing EMS and further worsening insulin imbalance in horses already affected. Additionally, illnesses such as colic, diarrhea, or pneumonia in overweight EMS horses can worsen metabolic problems and complicate treatments.
Treating Equine Metabolic Syndrome
When treating Equine Metabolic Syndrome, one of the first steps is to identify and resolve the main source of the problem. If diet and exercise alone aren’t enough, some horses with EMS may need medication to help improve their condition.
Weight Loss
Weight loss is key to managing EMS, as it helps improve insulin sensitivity and lowers overall health risks. If the horse is overweight, weight loss can be managed through increased exercise and dietary adjustments. The recommended weight loss rate for obese horses with EMS is between 0.5% and 1.0% of their body weight per week.
Testing for PPID (Cushing’s Disease)
Testing horses with EMS for PPID is important because Cushing's disease can worsen insulin resistance. Horses older than 15 years or those showing increased drinking, urination, or laminitis symptoms should be tested for PPID.
Common PPID tests include measuring adrenocorticotropic hormone (ACTH) or the more sensitive thyrotropin-releasing hormone (TRH) stimulation test, which measures ACTH after stimulation with thyrotropin-releasing hormone.
Dietary Changes
Dietary changes may be needed as proper nutrition is vital for horses with EMS. Managing calorie intake and minimizing NSCs helps promote weight loss and improve insulin regulation.
The type of horse feed and other feedstuffs fed may need to be altered while still meeting minimum feeding needs. Collaborating with a veterinarian and equine nutritionist is ideal for creating a balanced, individualized, nutrient-complete plan.
Forage and Pasture Grass Considerations
For EMS horses, forage should have low NSC—ideally under 10%—since it’s their primary sugar source. Bagged forage with a guaranteed NSC can be a reliable option.
Because NSC levels vary by growth and harvest, testing hay is recommended. Soaking hay helps lower its NSC content and can make it safer for sugar-sensitive horses, especially while waiting for hay test results. You can learn how to properly soak hay for EMS horses here.
Using a grazing muzzle during extended turnout on lush pasture helps reduce calorie and sugar intake, as grass can remain high in sugar beyond spring.
Medications
If diet and exercise aren’t enough to manage EMS, medications may help, including:
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Metformin: Reduces post-meal spikes in glucose and insulin, though its effectiveness may decline over time.
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Levothyroxine: Aids weight loss in horses resistant to diet and exercise.
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Pergolide: Used only when EMS occurs alongside PPID (Cushing’s Disease) as it helps regulate hormone imbalances from the pituitary gland.
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SGLT2 Inhibitors (e.g., canagliflozin, ertugliflozin): Increases glucose excretion in urine, reducing insulin levels and easing laminitis pain. Side effects include higher triglycerides and dehydration, requiring diet changes and salt supplements.
Feeding Horses with Equine Metabolic Syndrome Through Tribute® Equine Nutrition
Low NSC levels are essential when selecting feed because starch converts to sugar during digestion, causing the same metabolic reaction in the horse’s body.
Feeds like Kalm ‘N EZ® and Seniority® Low NSC are ideal for metabolically sensitive horses due to their low NSC content. Kalm ‘N EZ® contains 13.5% NSC, high digestible fiber, and moderate fat, supporting reduced feeding rates. Seniority® Low NSC is a 10% NSC complete feed and may also be used for total or partial hay replacement. Both feeds are suitable for adult horses of all ages, including those with sugar and starch sensitivities, as well as other metabolic issues.
Kalm ‘N EZ® Pelleted Versus Feeding Beet Pulp to Horses with EMS
A common go-to is feeding beet pulp to horses with EMS. Despite its lower NSC%, beet pulp can ultimately deliver more sugar, with any added nutrients, due to the higher volume required versus a low-NSC feed option like Kalm ‘N EZ® Pelleted, as seen in the comparison below.
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Beet Pulp
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NSC: 8%
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Fat: 0.5%
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Not fortified with essential nutrients
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Less calorie-dense, requires higher feeding volume
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Kalm ‘N EZ® Pelleted
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NSC: 13.5%
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Fat: 8%
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Fully fortified with essential nutrients
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More calorie-dense, so smaller portions are needed
Example feeding comparison of beet pulp versus Kalm ‘N EZ® Pelleted:
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4 lbs of Kalm ‘N EZ® delivers 0.54 lbs of NSC
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7 lbs of beet pulp delivers 0.56 lbs of NSC
Benefits of Essential K® Ration Balancer for EMS Horses
To meet nutritional needs while limiting NSCs, easy keepers with EMS do well on ration balancers like Essential K®.
However, some EMS horses require additional calories and nutrients. Harder keepers or hard-working horses may benefit from pairing Essential K® with a fat supplement like Wholesome Blends® Omega Plus or switching to Kalm ‘N EZ® Pelleted.
The benefits of Essential K® include:
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Delivers concentrated nutrients in small servings (1–2 lbs/day)
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Low in NSC (sugar and starch)
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Helps maintain or reduce weight
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Complements forage-based diets
Working with Tribute® to develop a free personalized feeding plan is an ideal way to ensure horses with Equine Metabolic Syndrome receive the right balance of nutrition tailored to their individual needs.
References
https://tributeequinenutrition.com/blogs/news/managing-cushings-disease
https://tributeequinenutrition.com/blogs/news/wellness-system
https://tributeequinenutrition.com/blogs/news/basics-of-nsc
https://tributeequinenutrition.com/products/seniority-pellet
