Equine Metabolic Syndrome

Generalized obesity and regional adiposity in a Morgan horse mare with Equine Metabolic Syndrome

Equine Metabolic Syndrome is both an endocrine and metabolic disorder and key components of this syndrome include enhanced metabolic efficiency, increased adiposity, insulin resistance (IR), and hyperinsulinemia. Most importantly, affected horses and ponies are predisposed to laminitis. This syndrome is more common in ponies, Morgan horses, Paso Finos, Arabians, and Warmbloods, and is likely to have a genetic component. Predisposed horses express the phenotype after gaining weight, so both inherent and environmental factors play a role in the development of EMS. Unrestricted pasture grazing leads to generalized obesity and this is a key feature of EMS in most cases. Regional adiposity also develops as adipose tissues expand within the neck region and other sites throughout the body. Enlargement of the neck crest is a physical characteristic that has been used as a phenotypic marker for EMS, with neck circumference being negatively correlated with insulin sensitivity in horses and ponies. Fat pads can also develop near the tailhead or within the prepuce or mammary gland regions. Many horses with EMS develop laminitis after being turned out on a new pasture or following rapid growth of grass in the spring or late summer. Obesity, regional adiposity, and IR are established risk factors for pasture-associated laminitis in ponies.