Equine metabolic syndrome

Equine metabolic syndrome (EMS) is an endocrinopathy affecting horses and ponies. It is of primary concern due to its link to obesity, insulin dysregulation, and subsequent laminitis. There are some similarities in clinical signs between EMS and pituitary pars intermedia dysfunction, also known as PPID or Cushing's disease, and some equines may develop both, but they are not the same condition, having different causes and different treatment. The cells of adipose (fat) tissue synthesizes hormones known as adipokines. In humans, dysfunction of adipose tissue, even in cases without obesity, has been associated with the development of insulin resistance, hypertension, systemic inflammation, and increased risk of blood clots (thrombosis). The inflammation produced by these hormones are thought to inflame adipose tissue, leading to the production of more adipokines and perpetuation of the cycle, and a constant low-level, pro-inflammatory state. Although it is suspected that a similar mechanism occurs in horses, further research is needed. Insulin dysregulation is commonly seen in horses with EMS, and is associated with obesity. This is similar to type II diabetes in humans, where the action of insulin is impaired, despite often elevated concentrations. It is of interest primarily because of its link to laminitis. Horses with EMS will have an increased insulin response after they are given oral sugars, which will cause a subsequent rise in blood insulin levels, or hyperinsulinemia. Hyperinsulinemia results in decreased tissue sensitivity to insulin, or insulin resistance, especially by the skeletal muscle, liver and adipose tissue. Tissue insulin resistance causes increased insulin secretion, which perpetuates the cycle. There does appear to be a strong link between decreased insulin sensitivity in obese animals; however, it is unknown which syndrome is the cause and which is the result. It is possible adipokines and cytokines made in adipose tissue down-regulate insulin pathways.