Equine Metabolic Syndrome
Managing insulin dysregulation and preventing laminitis in metabolically compromised horses: the latest research-based recommendations from experts
By Lucile Vigouroux, MSc
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Often referred to as the “modern horse’s plague,” equine metabolic syndrome (EMS) is a growing concern among horse owners and veterinarians—and for a good reason. This complex metabolic and endocrine disorder, marked by insulin dysregulation (ID) and obesity, significantly increases the risk of developing the painful hoof disease laminitis. In fact, researchers found that 89% of laminitic episodes admitted to one equine hospital in Finland were linked to underlying endocrine disease.
Modern horse management trends often favor high-sugar and -starch diets, prolonged stall confinement, and limited exercise, making EMS a true epidemic in our barns. We’ve turned to the latest research and recruited the knowledge of three industry-leading experts to help us understand the causes, mechanisms, clinical presentations, and management strategies of EMS, all of which are crucial to mitigating the harmful effects of this all-too-common condition.
EMS TERMINOLOGY
Hyperinsulinemia-associated laminitis (HAL): laminitis linked to insulin dysregulation (ID). Prior to 2024, the Equine Endocrinology Group referred to HAL as endocrinopathic laminitis.
Equine metabolic syndrome (EMS): a disorder that can occur in any equid, characterized by ID, abnormal fat storage, and an increased risk of laminitis.
Glucose: a simple sugar (monosaccharide) that serves as the body’s primary energy source.
Hyperinsulinemia: elevated insulin levels in the bloodstream. This can lead to other metabolic issues, including EMS and an increased risk of HAL.
Insulin: a hormone produced by the pancreas that helps regulate blood-sugar levels by signaling fat, muscle, and liver cells to take up glucose from the blood and store it as glycogen or use it as fuel for tissue energetics.
Insulin dysregulation (ID): hyperinsulinemia and tissue insulin resistance.
Insulin resistance (IR): a condition in which the body’s tissues become less sensitive to the actions of insulin, making it harder for the fat, muscle, and liver cells to transport the glucose out of the bloodstream and store it as glycogen.
The Mechanisms Behind ID and EMS
“EMS is a syndrome characterized by a set of risk factors that predispose horses to hyperinsulinemia-associated laminitis (HAL),” says Dr. Erica Macon of the Department of Animal Science at Texas A&M University. Insulin dysregulation, the central feature of EMS, involves an imbalance in blood-insulin concentrations.
In the healthy horse, insulin regulates blood sugar levels by facilitating glucose uptake into the body’s cells. When ID occurs, the body’s cells become less responsive to insulin, a phenomenon known as insulin resistance (IR). “Most scientists believe the hyperinsulinemia precedes IR, but that has not been solidified scientifically—that is just a working theory,” Macon says.
As Dr. Teresa Burns, who works in equine clinical sciences and research at The Ohio State University, further explains, EMS isn’t one single, straightforward issue: “Insulin dysregulation encompasses a variety of abnormalities of insulin and glucose dynamics, often including excessive insulin secretion from the pancreas and the relative ineffectiveness of this insulin in regulating blood glucose levels and other aspects of metabolism.” Burns highlights ID as a key factor in EMS that also increases the risk of laminitis, “as high levels of circulating insulin have been shown to directly contribute to this debilitating hoof condition.”
Let’s take a closer look at how EMS develops and how it can trigger laminitis in horses.
Erica Macon, MS, PAS, PhD,
is an assistant professor of equine science in the Department of Animal Science at Texas A&M University, in College Station. She specializes in equine nutrition and endocrinology, focusing on endocrine disorders. Her research centers on understanding the pathophysiology of hyperinsulinemia in efforts to develop therapies for hyperinsulinemia-associated laminitis, building on her extensive academic background and postdoctoral training in endocrinology.
Risk Factors and Causes of EMS
Research tells us nature and nurture can both take blame for the development of ID and EMS. “The causes of ID are multifactorial, including genetics, diet, obesity, excessive caloric intake, and physical activity,” Burns explains. Half of that equation—nurture—is within our control as horse owners and veterinarians in the form of strategic nutrition and exercise plans.
“Exercise—or the lack thereof—very much influences insulin sensitivity in both the short and long term,” she cautions. “Horses evolved as grazing animals designed to move and forage extensively throughout the day. In modern settings many are housed in relatively confined spaces with limited movement, which can increase their risk of developing ID and EMS.”
That’s not to say all equids exist on a level playing field when it comes to their risk of metabolic dysfunction. Burns explains that genetic predisposition determines which horses are more likely to develop EMS. “Certain breeds are genetically predisposed to metabolic efficiency, which makes them more vulnerable to ID when managed under conditions of energy excess (i.e., rich diets along with little exercise).”
Teresa Burns, DVM, PhD, Dipl. ACVIM,
is an associate professor of equine clinical sciences and research at The Ohio State University, in Columbus. As an internal medicine specialist, her research interests include endocrine disorders and laminitis in horses.
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A research team in England estimated in 2020 that a whopping 23.3% of their native pony and cob population has EMS1. Along the same lines, the Equine Endocrinology Group (EEG) has found pony breeds, Spanish breeds (i.e., Andalusians), gaited breeds (i.e., Saddlebreds, Paso Finos), Morgans, Miniature Horses, and Warmbloods are all overrepresented, and evidence exists of a genetic predisposition for EMS in Arabian horses2. These breeds have earned a reputation as easy keepers, gaining weight easily and needing very little feed to maintain their body weight and condition, and they are prone to obesity. These horses can quickly develop metabolic problems when kept in environments with abundant food, insufficient exercise, or both.
There’s still more to the equation. “Aside from genetic makeup, diet, and lifestyle, age and seasonality can influence the development and severity of ID,” Burns says. “For reasons that are still somewhat unclear, older horses tend to be at higher risk, and seasonal changes, particularly in the spring and summer, can cause fluctuations in insulin levels that may complicate management.”
The Nature vs. Nurture Debate
Have you ever been asked during a doctor’s appointment if diabetes runs in your family? Equids experience a similar genetic predisposition to ID and obesity, Macon says. “For some equids, genetics simply aren’t in their favor,” she explains. “Ponies and some horse breeds are more prone to being overweight and having ID. On the other hand, some horses that aren’t genetically predisposed can still develop ID due to a sedentary lifestyle and overfeeding.”
Additionally, we know that horses with pituitary pars intermedia dysfunction (PPID, formerly known as equine Cushing’s disease) are more likely to develop ID.
That being said, “there is no known link between EMS and PPID,” says Dr. Janice Kritchevsk of Purdue University’s College of Veterinary Medicine. “EMS is a syndrome, a collection of physical signs and laboratory findings. Some horses with PPID have the clinical signs and lab findings that put them in the EMS category,” she explains. “It is unknown why some horses with PPID are also insulin dysregulated, and others are not.”
Janice E. Kritchevsky, VMD, MS, Dipl. ACVIM
is a professor of large animal internal medicine at Purdue University’s College of Veterinary Medicine, in West Lafayette, Indiana. Her areas of research interest include endocrinology, mineral metabolism, equine pituitary pars intermedia dysfunction, and equine metabolic syndrome.
“There are evidently both genetic and environmental components to the development of ID in equids,” Macon says. The four main risk factors that increase the likelihood of ID include:
- Genetics.
- Lack of exercise.
- Overfeeding.
- Concurrent endocrine disease.
“EMS results from an interaction between genetic and environmental factors, and the risk of laminitis in the individual animal therefore depends on the cumulative effects of these influences,” the Equine Endocrinology Group (EEG) wrote in a 2022 publication titled Recommendations for the Diagnosis and Management of Equine Metabolic Syndrome (EMS)2. “There are high-genetic-risk animals that develop EMS with only mild environmental influences and other horses with lower genetic risk that develop EMS through exposure to improper environments.”
(Note: The EEG released its new recommendations in 2024.)
STORY CONTINUES BELOW
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Recognizing EMS—Clinical Signs
While obtaining a definitive diagnosis for EMS in horses requires blood testing, horse owners and caretakers should familiarize themselves with these common phenotypes (observable characteristics) and clinical signs of EMS:
Body condition score (BCS) of 7 or above
While not all horses with ID are obese, in one study researchers reported phenotypic indicators of obesity present in 95% of horses with basal (fasting) hyperinsulinemia without hirsutism (abnormal hair growth)3.
Localized fat deposits
Beyond generalized obesity, one of the most common clinical signs of EMS is the abnormal accumulation of fat in specific areas of the body, particularly the neck, shoulders, and tailhead. This often leads to the characteristic cresty neck, which is thickened and enlarged due to excessive fat storage. These fat deposits are a hallmark of EMS and often signal that a horse is at higher risk for ID and laminitis.
Laminitis
In horses with EMS, elevated insulin levels lead to a breakdown in the normal functioning of the laminae, which are the sensitive connective tissues that attach the coffin bone (P3) to the inside of the hoof wall. This results in inflammation, pain, and, in severe cases, irreversible damage that necessitates euthanasia. Again, the risk of laminitis—a condition that can be considered both a clinical sign and a result of EMS—increases with ID and hyperinsulinemia3.
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Where We Stand on EMS Diagnostic Testing
1. Clinical signs
Again, horses with EMS often show signs of obesity, abnormal fat deposits, and potentially lameness associated with laminitis. A cresty neck and generalized obesity can be strong indicators of ID and EMS. However, both false positives and false negatives are possible, Macon says.
“We now recognize new phenotypes that maintain a normal or healthy body condition score but still have resting hyperinsulinemia,” she explains. “These cases are particularly challenging to identify because, outwardly, the horse appears healthy.”
On the other hand, Macon has also seen morbidly obese draft horses with cresty necks that, to her surprise, had normal insulin levels, which she says can be quite baffling.
“The most perplexing cases are senior horses that are skinny but have abnormally high insulin concentrations,” she says. Because these misleading body types exist, relying on appearance alone isn’t enough to diagnose or rule out metabolic problems in horses, making blood testing necessary.
2. Oral sugar test (OST) and insulin tolerance test (ITT)
3. Measuring hyperinsulinemia
“Probably the most important concept that’s crystallized over the last 10-15 years is the primacy of hyperinsulinemia as the most important (known) risk factor for … HAL in horses and ponies with EMS,” Burns says. “Insulin concentration has become the biomarker that we monitor to assess a patient’s risk of laminitis and the most important target of therapeutic and management strategies we can test.”
4. Hoof radiographs
Because laminitis is a potential complication of EMS, veterinarians might take hoof radiographs to detect early signs of the condition, visible as rotation or sinking of the coffin bone. Establishing a baseline radiographic appearance of a horse’s front feet can also be valuable when evaluating potential bony changes as the disease progresses.
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Prevention and Management Strategies
Keeping the nefarious effects of EMS at bay involves a combination of careful monitoring, proper nutrition, appropriate exercise, and regular veterinary care. Some of the key strategies for preventing and managing EMS include:
1. Low-sugar/-starch diets
Experts agree that feeding a horse only the calories it needs is the most effective way to prevent ID and metabolic disorders. A calorie deficit leads to weight loss, and feeding EMS horses a diet low in the nonstructural carbohydrates (NSC) starch and sugar helps prevent harmful insulin spikes. “Low-carbohydrate, high-fiber diets are recommended for EMS horses,” says Kritchevsky.
2. Exercise
Regular physical activity plays a crucial role in managing EMS. Beyond supporting weight loss goals, “exercise is effective in improving insulin sensitivity,” Burns says. “As long as the horse is sound to work, regular aerobic exercise—such as riding, driving, or longeing—can promote weight loss, which is almost always one of our treatment goals for cases of EMS, at least initially.
“But even in the absence of an ounce of weight loss, peripheral insulin sensitivity is improved for at least two to four hours after a bout of exercise,” she continues. “As such, we should be prescribing exercise for these patients as an important part of their recovery, as long as they’re sound enough to do it.”
Realistically, though, acute laminitis often limits exercise for many horses with EMS.
3. Body condition and weight management
For overweight horses not yet diagnosed with metabolic disease, a gradual weight-loss plan supervised by a veterinarian or equine nutritionist can help reduce the risk of ID and laminitis. “If the horse is overweight, we should focus on reducing their overall calorie intake,” Kritchevsky says.
STORY CONTINUES BELOW
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The Link Between EMS and Laminitis
While EMS brings its health risks, its biggest threat to horses comes from its potential to cause laminitis. “Laminitis is definitely the most consequential concern for the life and soundness of the EMS-affected horse,” says Burns.
“Researchers Rumfola et al. (2022) stated that HAL is now the most common form of laminitis5,” Macon adds. “This finding aligns with the research of Karikoski et al. (2011), who reported that 89% of laminitis cases submitted to an equine hospital were linked to underlying endocrine disease3.”
“While EMS and its associated endocrine abnormalities usually develop gradually, almost imperceptibly over time (with age, with increasing adiposity, likely with many other factors), the clinical signs of (HAL) often present more acutely,” Burns says. “That said, of the big three types of laminitis (sepsis-associated laminitis, supporting-limb laminitis, and HAL), (HAL) is the most likely to be occult (not visible or easily detectable) or subclinical, slowly progressive over time with very little obvious clinical lameness until lamellar damage within the foot is more advanced.” This characteristic makes EMS a dangerous silent killer.
The Link Between EMS and Corticosteroid Joint Injections
“We know that certain degenerative disorders like osteoarthritis are common in performance horses, particularly as they age,” Dr. Teresa Burns says. “Joint therapies, such as biologics and corticosteroids, are often used to manage osteoarthritis (OA). The corticosteroid bit of that equation, however, has important effects on insulin and glucose dynamics, inducing (usually mild) insulin dysregulation for several days after administration.
“If the patient also has EMS, this effect is amplified, and management of OA now may represent a risk for a flare” of HAL, she continues. For these types of patients, veterinarians often turn to non-steroidal regenerative orthobiologics instead.
Insulin Resistance During Pregnancy is Normal
“As in most other mammalian species, pregnancy in horses is associated with gradual, acquired tissue insulin resistance over time,” Dr. Teresa Burns explains. “This is normal and represents a mechanism of maintaining an appropriate glucose supply to the developing fetus as it grows.”
However, as one might expect, in mares with EMS and IR before they become pregnant, this gestational exacerbation of ID can be enough to induce clinical laminitis, she explains. Ensuring metabolic health and normal body condition prior to breeding plays a crucial role in minimizing laminitis risk for broodmares.
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Advancements in Treating Insulin Dysregulation and EMS
Just as with human prediabetes, there isn’t a cure, per se, for EMS, and veterinarians’ focus remains on prevention and management. Recently, however, researchers have provided an important piece of the puzzle regarding the role of dopamine in insulin regulation, Macon says.
“Two studies recently published revealed that dopamine receptors are present on pancreatic beta cells, and that dopamine plays a role in inhibiting insulin secretion,” she explains. “Although these studies were conducted in healthy horses and need to be replicated in horses with endocrine diseases, the findings are groundbreaking.
“That’s primarily because there is currently no drug therapy specifically targeting insulin secretion, which is the primary issue for horses suffering from hyperinsulinemia,” Macon continues. “Unlike humans with prediabetes or Type 2 diabetes, horses rarely experience altered glucose homeostasis; they primarily exhibit hyperinsulinemia. As a result, treatments like metformin, which are effective in humans with prediabetes and diabetes mellitus, have proven less effective in horses with this condition.”
A promising area of research involves using sodium-glucose cotransporter-2 (SGLT2) inhibitors, say both Macon and Burns. This drug class encompasses the human diabetes medications canagliflozin and ertugliflozin, which—at least in people—reduce blood sugar through increased glucose excretion in urine. In a 2025 study, researchers found that these SGLT2 inhibitor drugs can reduce hyperinsulinemia in horses8. “One case study of a pony suffering from EL was seen running around without lameness after treatment with an SGLT2 inhibitor,” Macon reports. “An exciting and promising outcome!”
“SGLT2 inhibitors really burst onto the scene a few years ago and seem poised to revolutionize the acute and chronic care of (HAL),” Burns agrees. “Horses with (HAL) are now candidates for rehabilitation and recovery.”
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Final Thoughts
What’s the long-term prognosis for a metabolically compromised horse? “There’s hope for (HAL) patients,” says Burns. “These horses aren’t done for, and that mindset is probably one of the most important ways our understanding of EMS has evolved over the past decade.
“That being said, given the reliable genetic predispositions to EMS, it would probably be a misstep to say that EMS can be cured,” she adds. “The clinical signs and metabolic abnormalities can be managed to a point at which they are normalized or no longer detectable—in that case, the clinical syndrome could be said to be reversed. But the underlying genetic predisposition likely remains.”
This highlights the need for lifelong management and monitoring of horses with equine metabolic syndrome. As research into ID continues to evolve, our sources say promising new treatment options might become available, offering hope for improved health and quality of life for our metabolically challenged equids.
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Credits
Lucile Vigouroux, MSc,
is a New-York-based freelance author with a passion for equine health and veterinary care. She holds a master’s degree in equine performance, health, and welfare from Nottingham Trent University, in the U.K., and an equine veterinary assistant certification from AAEVT. Vigouroux also runs a small equine PEMF therapy business.
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