Diagnosis and management of equine metabolic syndrome

Abstract

Equine metabolic syndrome (EMS) is a prevalent endocrine disorder that increases the risk of hyperinsulinaemia-associated laminitis (HAL), the most common and clinically significant form of laminitis. The central pathological feature of EMS is insulin dysregulation (ID), which encompasses basal or postprandial hyperinsulinaemia and tissue insulin resistance. Although obesity is a frequent finding, EMS can occur in lean animals, and not all obese horses are affected, necessitating objective diagnostic testing rather than reliance on body condition alone. Excessive dietary nonstructural carbohydrates (NSC), reduced hepatic insulin clearance, and impaired insulin signalling contribute to sustained hyperinsulinaemia which induces laminitis. Environmental and management factors, particularly high-NSC diets, unrestricted pasture access and physical inactivity, are the primary drivers of EMS development. Obesity exacerbates metabolic dysfunction through suspected adipose-derived inflammation. Age and genetic predisposition further influence risk, with ponies and certain breeds being disproportionately affected. Diagnosis focuses on identifying ID. Basal insulin measurement is specific but insensitive, while dynamic tests, particularly the oral sugar test, are more reliable for detecting exaggerated postprandial insulin responses and assessing laminitis risk. Tests of insulin resistance, such as the insulin tolerance test, provide complementary information. Management is centred on strict dietary NSC restriction, controlled forage intake and elimination or careful management of pasture access. Regular exercise improves insulin sensitivity but must be adapted to laminitic status. Appropriate hoof care is essential given the high prevalence of chronic and recurrent laminitis. Pharmacological therapy, including sodium-glucose cotransporter-2 inhibitors, may be indicated when nonpharmaceutical measures fail but should be considered adjunctive and individualised. Prognosis is favourable when EMS is recognised early and managed rigorously. Outcomes worsen with recurrent or chronic HAL, underscoring the importance of early detection, sustained management and close collaboration between veterinarians, farriers and owners.