Equine Metabolic Syndrome: Signs, Management and Diet

Reviewed by Dr. Ali Ehtisham, DVM

Equine Metabolic Syndrome (EMS) is one of the most significant health challenges facing horses and ponies in the developed world. It is a primary endocrine disorder characterised by insulin dysregulation, regional obesity, and a dramatically elevated risk of laminitis — the painful, potentially career-ending inflammation of the laminar tissue within the hoof. EMS affects horses and ponies of many breeds, but certain types are particularly susceptible, and the condition is strongly influenced by management practices that can be meaningfully modified. Understanding EMS — what it is, how to identify it, and how to manage it effectively — is essential knowledge for owners of ponies and any breed with a tendency toward easy weight gain.

What Is Equine Metabolic Syndrome?

EMS is fundamentally a disorder of insulin regulation. In a healthy horse, dietary carbohydrates — sugars and starches from grass and feed — trigger a measured release of insulin from the pancreas to facilitate glucose uptake by cells. In a horse with EMS, this response is dysregulated: insulin secretion is excessive and/or the body's cells respond abnormally to it, a state described as insulin resistance or, more precisely, insulin dysregulation.

The consequences of insulin dysregulation extend well beyond blood sugar control. High circulating insulin levels have a direct damaging effect on the vascular supply to the laminae — the sensitive connective tissue structures within the hoof that suspend the coffin bone from the hoof wall. Insulin appears to activate insulin-like growth factor receptors in lamellar tissue, triggering an inflammatory cascade that disrupts the lamellar architecture. This is the mechanism by which EMS horses develop laminitis, and it explains why laminitic episodes in EMS horses are often associated with dietary triggers — periods of high grass sugar content, or access to hard feed — rather than the mechanical loading traditionally associated with pasture-associated laminitis.

EMS is distinct from but often confused with Pituitary Pars Intermedia Dysfunction (PPID, commonly called Cushing's disease). Both conditions involve insulin dysregulation and both are associated with laminitis, but they have different mechanisms, different typical presentations, and different treatment approaches. PPID is a progressive neurodegenerative disease primarily affecting older horses that is associated with elevated ACTH levels and characteristic additional signs including hypertrichosis (long, curly coat), muscle wastage, and increased urination. Both conditions can co-exist in the same animal, which is relatively common in older obese horses.

Clinical Signs of EMS

The clinical signs of EMS are variable, and not all affected horses display every feature. The most consistent findings are:

Obesity and abnormal fat deposition are central to the EMS presentation. Affected horses typically carry a body condition score above 6 on the Henneke scale and may appear generally obese. However, the distinctive feature of EMS is the pattern of fat distribution rather than simply generalised obesity. A cresty neck — a pronounced, firm, often asymmetric ridge of fat along the crest of the neck — is the most characteristic sign. Fat deposits behind the shoulder, over the tailhead and loins, and in the sheath or mammary gland area are also typical. These regional fat deposits (also called adiposities) can be present even in horses that are not grossly obese.

Laminitis — recurrent or chronic — is frequently the presenting complaint that brings EMS horses to veterinary attention. Laminitis in EMS horses typically occurs seasonally in spring and autumn when pasture sugar content peaks, though it can occur at any time of year if dietary management is poor. Affected horses show the characteristic signs of laminitis: heat in the hooves, bounding digital pulses, a rocked-back stance to shift weight away from the painful forefeet, and reluctance to move.

Exercise intolerance and lethargy are reported by many owners of EMS horses, though these signs are non-specific. Mares may show irregular oestrous cycles. Hypertriglyceridaemia can develop in horses with severe metabolic dysfunction.

At-Risk Breeds

Native and cold-blooded pony breeds carry the highest risk of EMS, reflecting their evolutionary history of surviving on sparse, poor-quality forage. Breeds with the highest reported prevalence include Welsh Ponies and Cobs, Dartmoor, New Forest, Fell, Connemara, and Norwegian Fjord horses. Among horse breeds, Andalusians, Lusitanos, Morgans, and certain warmblood lines are recognised as having elevated susceptibility. However, EMS is not restricted to these types — any horse can develop the condition if management creates the right environment. The key modifiable risk factors are obesity, a high-carbohydrate diet, and inadequate exercise, all of which are common in domestic horses regardless of breed.

Diagnosis

Diagnosis of EMS requires demonstration of insulin dysregulation through blood testing, combined with a thorough clinical examination. A resting insulin level measured on a fasted blood sample is the simplest initial test, though its sensitivity is limited — some dysregulated horses have normal resting insulin levels. The oral sugar test (OST) is more sensitive: a measured dose of corn syrup is administered orally and insulin is measured 60 to 90 minutes later. An exaggerated insulin response — above the laboratory's reference range — confirms dysregulation and supports an EMS diagnosis. In horses where PPID is also suspected, ACTH measurement and/or TRH stimulation testing is performed alongside. Body condition scoring and assessment of cresty neck score (a separate 0–5 scale for scoring neck fat) complement the laboratory workup. For a comprehensive overview of equine health conditions, explore our full collection of horse health and care guides.

Management: Diet and Grazing

Dietary management is the single most impactful intervention for EMS, and it must be maintained consistently and year-round — not just when the horse shows signs of laminitis. The core principle is reducing dietary water-soluble carbohydrate (WSC) intake to a level the dysregulated insulin system can handle.

Pasture restriction is non-negotiable for most EMS horses. Lush, rapidly growing grass — particularly spring flush grass and autumn regrowth — is extremely high in sugars and fructans and is the most common trigger for laminitis episodes. EMS horses should not have free access to pasture without restriction. Strip grazing divides pasture into small daily allocations that reduce intake while maintaining some turnout and natural behaviour. A well-fitted grazing muzzle reduces grass intake by 30 to 80 percent while allowing the horse to be turned out for exercise and social interaction. Bare paddocks or track systems are often the safest environments for severely affected horses during the highest-risk seasons.

Hay and forage should be tested for WSC content where possible; values below 10 percent WSC on a dry matter basis are recommended for EMS horses. Soaking hay in cold water for 30 to 60 minutes reduces WSC content by up to 30 percent and is a practical tool when hay analysis is not feasible. Hard feed should be limited to a low-sugar, low-starch vitamin and mineral balancer — not a calorie-dense compound feed. All molassed products, high-starch cereal feeds, and high-sugar treats should be eliminated.

Exercise and Medication

Regular exercise has multiple benefits for EMS horses: it improves insulin sensitivity, promotes weight loss, and maintains cardiovascular and musculoskeletal health. Even gentle, regular exercise — daily in-hand walking, light ridden work — produces measurable improvements in insulin regulation over time. Exercise must be contraindicated during active laminitis episodes — working a horse through laminitis causes further structural damage — but should be resumed progressively as soon as veterinary clearance is given following recovery.

Levothyroxine sodium is sometimes prescribed for EMS horses where dietary and exercise management alone has not produced adequate improvement. It accelerates metabolism, promotes weight loss, and has been shown to improve insulin sensitivity in equine studies. It is used for defined treatment periods of three to six months and requires veterinary supervision and monitoring. Metformin, widely used in human type 2 diabetes, has limited oral bioavailability in horses and variable clinical evidence; its use is less common in equine practice than levothyroxine. Medication supports but does not replace dietary management — a horse on levothyroxine that continues to consume high-WSC pasture will not improve.

Laminitis Prevention

For EMS horses, laminitis prevention is a year-round management commitment. The practical components are: maintaining appropriate body condition (BCS 4.5 to 5 maximum); restricting pasture access during the highest-risk periods (spring growth and autumn flush, particularly in cool-but-bright weather when grass accumulates non-structural carbohydrates); feeding low-WSC hay and eliminating all high-sugar feed; providing regular exercise; monitoring digital pulses and hoof temperature routinely so that any deterioration is detected early; and scheduling regular veterinary check-ups including repeat insulin testing to assess whether management is maintaining adequate control.

Frequently Asked Questions

What is the difference between EMS and PPID (Cushing's disease) in horses?

EMS is a primary insulin dysregulation disorder associated with obesity, affecting horses of any age. PPID is a progressive neurodegenerative pituitary gland disease primarily affecting older horses over 15 years, characterised by elevated ACTH and additional signs including a long curly coat, muscle wastage, and increased urination. Both involve insulin dysregulation and laminitis risk; both can occur in the same horse.

Which breeds are most at risk of Equine Metabolic Syndrome?

Native pony breeds — Welsh, Dartmoor, Fell, New Forest, Connemara, Norwegian Fjord — carry the highest prevalence. Among horse breeds, Andalusians, Morgans, and some warmbloods are also recognised as higher risk. However, any horse managed with high-carbohydrate diet and insufficient exercise can develop EMS regardless of breed.

How is Equine Metabolic Syndrome diagnosed?

Diagnosis requires blood testing to demonstrate insulin dysregulation. Resting insulin measurement is the initial test; the oral sugar test (OST) is more sensitive and is used when resting insulin is normal but EMS remains suspected. Clinical examination including body condition scoring and cresty neck assessment complements the laboratory workup.

What should an EMS horse eat?

The dietary foundation is low-WSC hay or haylage, ideally tested below 10 percent WSC on a dry matter basis or soaked before feeding. Pasture must be strictly restricted, particularly during high-risk spring and autumn periods. Hard feed should be limited to a low-calorie vitamin and mineral balancer. All high-sugar feeds, molassed products, and starchy cereals should be eliminated.

Is medication necessary for all horses with EMS?

No — most EMS horses can be managed effectively through diet and exercise alone. Medication (levothyroxine or metformin) is considered when dietary and lifestyle management has not produced adequate improvement over three to six months, or when severe or recurrent laminitis demands more aggressive intervention. Medication supports but does not replace dietary management.

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Disclaimer: This article is for educational purposes only and does not constitute veterinary advice. Always consult a licensed equine veterinarian for diagnosis and treatment.