Horse Equine Metabolic Syndrome (EMS) and Welfare

Equine metabolic syndrome is a common hormonal disorder in horses and ponies, closely linked to obesity and pasture management. Its most serious welfare consequence is recurrent laminitis.

Key Facts

Equine metabolic syndrome (EMS) is characterised by insulin dysregulation (previously called insulin resistance) and a predisposition to pasture-associated laminitis
Affected horses and ponies often show regional adiposity — fat deposits at the crest of the neck, behind the shoulder, around the tailhead, and in the sheath of male horses
Native and draft breeds (Welsh Ponies, Connemara, Highland, Dartmoor, Shetland, Andalusian, Morgan) are particularly predisposed — these breeds evolved on sparse forage and are physiologically ill-adapted to modern rich pasture
The key mechanism: non-structural carbohydrates (NSC) in pasture (particularly spring flush and autumn regrowth) trigger exaggerated insulin responses in EMS-affected horses, which activates laminitis cascades in the hoof
Diagnosis involves dynamic insulin testing (the oral sugar test, OST): blood insulin measured 60–90 minutes after corn syrup administration; elevated insulin confirms insulin dysregulation
Management involves strict dietary NSC restriction, appropriate exercise (when not laminitic), weight management, and in some cases medication (levothyroxine, metformin, pergolide if PPID co-exists)
EMS frequently co-exists with Pituitary Pars Intermedia Dysfunction (PPID/Equine Cushing's) in older horses — both conditions predispose to laminitis through different mechanisms
Prevention through appropriate body condition management and restricting access to high-NSC pasture is more effective and welfare-positive than managing repeated laminitis episodes

Welfare Considerations

EMS is a welfare-critical condition primarily because of its role in recurrent laminitis — one of the most painful conditions in equine medicine. The chronic pain of laminitis, the repeated acute crises, and the potential for permanent structural hoof damage (rotation and sinking of the pedal bone) cause profound suffering. Many EMS horses cycle through repeated laminitis episodes for years before adequate diagnosis and management are implemented. The welfare challenge is that management requires significant owner commitment to pasture restriction, dietary change, and often permanent lifestyle modification — including limiting or eliminating grazing for pasture-sensitive individuals. Adequate analgesia during laminitis episodes and proactive prevention through appropriate body condition management are the two most important welfare priorities.

What You Can Do

Learn to body condition score your horse regularly — aim for BCS 4–5/9 in native and draft breeds prone to EMS
Restrict pasture access during high-risk periods (spring flush, autumn regrowth) for susceptible breeds
If laminitis occurs, pursue insulin testing to identify and manage underlying EMS alongside the acute episode
Implement soaking or steaming hay to reduce NSC content for horses on restricted diets
Discuss whether concurrent PPID should be tested and managed alongside EMS in horses over 15 years old