Fat, Foundered Horses: What Is Equine Metabolic Syndrome?

Middle-aged obesity (body condition score 7-9 on a scale of 1 to 9) accompanied by insidious-onset laminitis is a syndrome that has been recognized by equine practitioners for decades. Equine metabolic syndrome (EMS) is a recently coined name that has gained acceptance to describe this condition. Clinical signs of laminitis commonly develop while horses are grazing spring pasture but can also occur at other times of the year and in horses without pasture access. Affected horses tend to be aged between 10-to-20 years and there does not appear to be a sex predilection. Pony breeds, domesticated Spanish mustangs, Peruvian Pasos, Paso Finos, Andalusians, European Warmbloods, American Saddlebreds, Arabians, and Morgan horses are more commonly affected than Thoroughbreds, Standardbreds, and Quarter Horses. This breed disparity is supportive of a genetic predisposition. In the past, this syndrome was commonly attributed to hypothyroidism or pituitary pars intermedia dysfunction (PPID or classic equine Cushing’s disease); however, most affected horses do not manifest additional clinical signs or endocrinologic test results to support these conditions. It is now recognized that insulin resistance is the primary endocrinopathy induced by obesity in EMS-affected horses. [...]