Defining Equine Metabolic Syndrome (EMS)

What is Equine Metabolic Syndrome (EMS)?  EMS was first recognized as a problematic health condition of the obese, “easy keeper” or “good doer” type horse in 2002 by Dr P.J. Johnson.  A major advance came in 2010 when a Consensus Statement of the American College of Veterinary Internal Medicine (ACVIM) panel of experts (Veterinarians, Clinicians and Researchers) formally recognized EMS as a clinical syndrome of the horse and provided the veterinary community with information characterizing and defining EMS horses.  The challenge remains in continuing to educate veterinarians and horse owners about the seriousness of the EMS condition.  Thus, our goal is to help everyone better understand and bring awareness to the condition of EMS.

Link: ACVIM Consensus Statement on EMS

While statistics disclosing the percentage of horses suffering from EMS are scarce, one needs only to peruse the popular equine press to locate a myriad of articles on the subject of “obesity” and/or “EMS” to find ample evidence that EMS is a major concern for the horse population.  While not all obese horses are going to be EMS, obesity is observed in the majority of cases. Unfortunately, EMS is a complex disorder with many unknowns remaining to be answered.  To date, there are no epidemiology studies of EMS.  Although, anecdotal evidence suggests that middle aged horses (5 to 15 yrs) are mostly affected and that certain breeds may be predisposed to EMS, such as some pony breeds (Welsh and Shetland) and horse breeds (Morgans, Paso Finos, Arabians, Spanish Mustangs, Quarter Horses and Arabians).

The 3 main criteria for classifying a horse as EMS are as follows:

1) Increased “general” or “regional” adiposity.  General obesity is observed in the majority of EMS horses, but some affected horses will have a leaner overall body condition and regional adiposity or fat accumulation, while others are normal in appearance. Regional adiposity involves fat accumulation on the top of the neck (“cresty neck” appearance) and/or in “fat pads” close to the tail head, behind the shoulder or in the mammary gland region.

Areas of Fat Accumulation with Regional Adiposity

Areas of Fat Accumulation with Regional Adiposity

2) Insulin Resistance (IR) or decreased insulin sensitivity can be simply defined as a failure of insulin to stimulate glucose uptake by metabolically active tissues (muscle, fat and liver) when nutrients are abundant after feeding. Glucose is not readily transported into the cells in animals with insulin resistance. To compensate for insulin resistance, the pancreas of IR animals typically produces and secretes larger amounts of insulin to promote entry of glucose into cells. The high levels of blood insulin associated with insulin resistance is a condition known as hyperinsulinemia which can contribute to increased risk of laminitis or “founder.”

3) A predisposition toward developing Laminitis. Laminitis or “founder” is a devastating condition of the hoof that involves the breakdown of the hoof lamellar interface that connects the coffin bone to the hoof wall. Laminitis results from chronic inflammation and reduced blood flow to the lamellar interface and can lead to euthanasia.  Laminitis in EMS horses may be clinical or subclinical and occurs in the absence of grain overload, colic, colitis, retained placenta or infectious/sepsis.