Veterinarian medical care of horses

Equine Metabolic Syndrome in Performance Horses: Why Even Fit Competition Horses Are at Risk—and How Steroids Can Exacerbate It

Equine Metabolic Syndrome (EMS) is no longer considered a condition limited to easy-keeping, inactive horses. Research shows it’s increasingly diagnosed in performance horses that appear lean and are in regular work.

In many cases, EMS in performance horses remains undiagnosed until a laminitic episode occurs or a routine corticosteroid treatment triggers a metabolic response.

In this article, we explore why fit horses remain at risk for insulin resistance, how steroids can exacerbate EMS, and the practical nutrition and management strategies that help protect long-term soundness and metabolic health.

Understanding Equine Metabolic Syndrome

Equine Metabolic Syndrome (EMS) develops when a horse’s body no longer responds normally to insulin. This results in insulin dysregulation and persistently elevated insulin levels (hyperinsulinemia)—even when blood glucose appears normal. After consuming high-starch or high-sugar feeds, affected horses experience exaggerated and prolonged insulin spikes that contribute to ongoing metabolic dysfunction.

One of the most serious consequences of EMS is laminitis. Sustained high insulin levels damage the sensitive lamellae within the hoof, weakening the attachment between the hoof wall and coffin bone. 

Laminitis may appear suddenly, sometimes after diet changes or medical treatments. In severe cases, metabolic imbalance can also lead to complications such as hyperlipemia—a dangerous buildup of fat in the bloodstream—if excessive fat mobilization overwhelms the liver.

EMS in Performance Horses: Genetic Risk and Why Body Condition Alone Doesn’t Prevent Insulin Dysregulation

EMS has traditionally been associated with overweight, inactive, or easy-keeping horses. However, it is now increasingly recognized in fit, actively working horses.

EMS stems from insulin resistance in horses, not just excess body fat. Because of this underlying metabolic dysfunction, even moderate-weight or leaner performance horses can develop abnormal insulin responses.

Dismissing EMS based on body condition alone often delays diagnosis and increases the risk of preventable complications, including laminitis. This helps explain why EMS in performance horses can appear unexpectedly, especially following diet changes or medical treatments such as corticosteroids. Because corticosteroids and insulin resistance are closely linked, steroid use can trigger metabolically susceptible horses and further elevate laminitis risk.

As awareness has expanded, veterinarians now assess metabolic risk more comprehensively. Rather than focusing solely on obesity, clinicians watch for subtle signs of chronic laminitis and screen earlier for insulin dysregulation—especially when diet shifts or steroid use are involved. 

Genetics & Breed Risk

Some horses—particularly certain breeds—are genetically predisposed to metabolic dysfunction, and genetic risk does not exclude athletic individuals. That’s why managing EMS in competition horses requires careful attention to both inherited predisposition and environmental influences

Even in breeds traditionally considered lower risk—such as Thoroughbreds and Standardbreds—weight, dietary factors, and management practices can still trigger metabolic issues.

Breeds with a higher risk of insulin dysregulation include:

  • Ponies such as Welsh, Shetland, and Dartmoor ponies
  • Andalusians, Lusitanos, and other Iberian breeds
  • Arabians
  • Morgans
  • Saddlebreds
  • Quarter Horses
  • Donkeys
  • Mustangs
  • Miniature horses

Diet

Diet plays a major role in the development of insulin resistance in horses. High intake of non-structural carbohydrates (NSCs)—sugars and starches—can worsen metabolic instability and increase the likelihood of developing EMS in predisposed horses. Even in fit athletes, repeated insulin spikes after high-starch meals can contribute to persistent hyperinsulinemia in horses.

Some horses maintain a normal Body Condition Score (BCS), including appropriate rib coverage, yet still develop abnormal fat deposits along the crest, tailhead, or behind the shoulders. Others remain lean but still metabolically sensitive.

Strategic nutrition for insulin-resistant (IR) performance horses focuses on reducing NSCs—sugars and starches. Instead, high-fat and high-fiber ingredients provide “cool calories” to support athletic performance.

This approach provides the needed energy while limiting insulin spikes and reducing the risk of laminitis, helping prevent metabolic issues in performance horses.

Performance Stress and Competition Demands

Competition demands can further strain metabolic balance. Travel, frequent showing, intense conditioning, and changes in routine elevate cortisol and other stress hormones. Over time, these hormonal shifts influence glucose metabolism and may reduce insulin sensitivity, increasing the risk of EMS even in fit, active horses.

While regular exercise can improve insulin sensitivity, it does not override genetic predisposition—some horses remain metabolically vulnerable despite being in full work. When chronic stress combines with high-energy diets or medical treatments that affect glucose regulation, it can tip a horse toward insulin dysregulation.

How Corticosteroids Can Trigger or Exacerbate EMS

Steroid use is common in performance horses, but understanding the link between corticosteroids and insulin resistance is vital when managing Equine Metabolic Syndrome.

Steroids—whether given systemically, injected into joints, inhaled, or applied topically—can worsen metabolic instability and increase the risk of steroid-induced laminitis in horses, particularly in those with underlying insulin dysregulation.

Insulin levels rise within 24 to 48 hours after a single steroid dose, sometimes reaching ranges associated with laminitis risk. While healthy horses often recover quickly, horses with insulin resistance or persistent hyperinsulinemia may experience a more severe and prolonged response, increasing the risk of laminitis.

Treating and Managing EMS in Active Performance Horses

Proactive management remains central to the care of EMS in performance horses. Once diagnosed, the focus shifts to maintaining long-term metabolic stability through careful monitoring and targeted nutrition while still supporting athletic demands.

While nutrition is the foundation of management, some horses require medical support. In more severe cases, medications may help regulate insulin response.

There is also growing interest in SGLT2 inhibitors to reduce hyperinsulinemia and hyperglycemia, with ongoing research evaluating their role in improving safety for horses receiving corticosteroid therapy and their place in EMS management.

Diet & Nutrition

Managing EMS in actively training or competing horses requires balancing metabolic control with adequate energy intake.

A forage-first approach should prioritize tested low-NSC forage (ideally below 10–12%) as the foundation of the diet. When needed, soaking hay can further reduce the water-soluble carbohydrate content. Pasture grass—especially in the spring and fall—may also need to be limited, as it can contain higher levels of sugar that increase insulin response and laminitis risk.

Additional calories and nutrients for horses in work can be supplied through carefully selected concentrates with controlled NSC levels rather than high-sugar, high-starch feeds. In some cases, ration balancers can be used instead of grain concentrates to meet essential nutrient requirements without adding excess NSCs or unnecessary calories.

Reducing EMS Risk During Steroid Treatment

In some cases, steroid use in horses is necessary—or even life-saving. Corticosteroids remain essential for managing serious conditions such as asthma, osteoarthritis, and immune-mediated disease. As a result, the focus has shifted from avoiding steroids altogether to carefully mitigating metabolic risk when they are required.

For horses already at metabolic risk, the goal is to minimize the chance of triggering laminitis. When higher doses of steroids are necessary, dietary management becomes even more critical.

Feeding only tested, low-NSC hay, and managing pasture grass intake combined with careful concentrate selection can help limit the risk of steroid-induced laminitis in insulin-sensitive horses. Because steroids independently raise blood glucose and insulin levels, combining them with high-NSC feeds significantly increases metabolic risk.

After steroid treatment, owners and trainers should closely monitor for subtle warning signs such as weight shifting, stronger digital pulses, or increased hoof warmth. Endocrinopathic laminitis often develops gradually and can be easy to overlook without careful observation. 

Blood Testing Before Steroid Use

For horses with known risk factors for insulin dysregulation, proactive testing and careful planning can significantly reduce risk during steroid treatment. The decision to perform pre-steroid screening should be based on individual factors such as age, breed, discipline, and metabolic history.

While universal testing is not always necessary, horses in higher-risk categories benefit from blood testing before corticosteroid use. Early identification of insulin resistance in horses allows veterinarians to adjust treatment plans or consider alternatives when appropriate. Advances in stall-side insulin testing have also made screening more accessible and practical.

Tribute Equine Nutrition: Supporting Performance Horses with EMS

Managing Equine Metabolic Syndrome in active horses means balancing insulin control with the energy demands of performance. Horses with insulin dysregulation still require adequate calories, quality protein, and digestible energy—the key is meeting those needs while minimizing hyperinsulinemia.

When extra energy is needed, fat and highly digestible fiber can replace high starch grains to support performance without exacerbating insulin dysregulation. Tribute’s horse feed formulations feature controlled NSC levels, quality fat, and balanced amino acids to maintain muscle and metabolic stability. 

Tribute follows a forage-first approach as its foundation, with carefully selected concentrates to create a balanced, performance-supporting diet. For horses in work that require additional calories without excessive NSCs, Tribute offers several appropriate options:

  • Kalm ‘N EZ® – A low-NSC, controlled-starch feed designed to support horses with metabolic concerns while still providing performance-level nutrition. Its higher fat and fiber content supplies energy without triggering large insulin spikes, making it well-suited for managing EMS in competition horses.
  • Synergize® – A high-fat and fiber, controlled-starch performance feed formulated to support muscle development, topline, and sustained energy. It provides calorie-dense nutrition with lower starch levels than traditional grain-based feeds, making it appropriate for many performance horses.
  • Seniority® Low NSC – Ideal for metabolically sensitive horses that benefit from highly digestible fiber and controlled sugar and starch intake. Though formulated for seniors, it works well for horses of any age requiring metabolic support.
  • Essential K® or Wholesome Blends Balancer® – Ration balancers that deliver concentrated vitamins, minerals, and amino acids without unnecessary calories or NSCs, ideal for easy keepers maintaining weight on forage.

Because each horse’s workload and metabolic sensitivity are unique, Tribute Equine Nutrition offers a free, personalized feeding plan to help fine-tune nutrition and support long-term soundness in performance horses with EMS.

References

Article By:
Chris Mortensen, Ph.D.
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