Equine Metabolic Syndrome (EMS) is a complex endocrine disorder characterised by insulin dysregulation (ID), regional adiposity, and predisposition to endocrinopathic laminitis. It represents one of the most significant welfare challenges in native pony breeds and easy-keeping horse types kept in modern management systems.
Pathophysiology
EMS involves dysregulation of insulin signalling — affected horses and ponies show exaggerated insulin responses to dietary carbohydrate (non-structural carbohydrate, NSC) intake. Persistently elevated insulin levels trigger laminar events in the hoof, causing laminitis without the classic inflammatory triggers. Regional fat deposition — particularly the cresty neck score (CNS), shoulder pads, and tailhead — is characteristic. Leptin resistance and hypothalamic-pituitary axis changes are also involved.
Susceptible Breeds
Native breeds — Welsh Ponies, Dartmoor, New Forest, Shetland Ponies, Thoroughbred crosses, Andalusians, Paso Finos, and Morgans — are disproportionately represented. These breeds evolved on sparse, high-fibre, low-NSC forage and are physiologically mismatched to the calorie-dense feeds and rich pasture typical of modern horse management.
Clinical Signs
- Obesity or regional adiposity (cresty neck score ≥3)
- Recurrent or chronic laminitis (most important welfare consequence)
- Increased dietary carbohydrate sensitivity — laminitis triggered by grass access or dietary changes
- Polydipsia and polyuria in some cases
- Reproductive abnormalities
Diagnosis
Oral sugar test (OST) using Karo syrup: samples blood glucose and insulin at 0, 60, and 90 minutes post-administration. Elevated insulin at 60–90 minutes confirms ID. Resting insulin and glucose may also be measured. Differentiating from PPID (Pituitary Pars Intermedia Dysfunction, "Cushing's disease") is important — many horses have both conditions.
Management
Dietary management: Primary intervention. Restrict access to high-NSC pasture — strip grazing, track systems, or dry lot management with hay (soaked if high sugar). Target hay NSC <12% DM; soaking hay for 30–60 minutes in cold water reduces NSC by 20–30%. Eliminate hard feed concentrates unless nutritional supplementation is needed for specific deficiencies.
Weight management: Achieve BCS of 4–5/9 (UK 2.5–3/5) through controlled hay rationing (1.5% BW/day DM for weight loss).
Exercise: Regular moderate exercise improves insulin sensitivity — essential component of EMS management unless limited by active laminitis.
Welfare Significance
EMS-associated laminitis causes severe, often chronic pain — it is one of the leading causes of equine euthanasia. Proactive management of susceptible breeds — restricting pasture access, monitoring body condition, and early dietary intervention at first signs of cresty neck development — prevents laminitis and dramatically improves welfare outcomes.