Equine Metabolic Syndrome (EMS) is a cluster of metabolic disorders including obesity, abnormal fat deposition around the body, insulin resistance (IR) and high levels of insulin in the blood stream. It is similar, but not identical, to Type II Diabetes in humans.


The outward clinical signs of EMS include changes in body condition and problems seen due to the medical complications seen with this syndrome. Clinical signs associated with EMS include: 

  • Obesity, though not all cases of EMS have an overall increased body condition.
  • Regional adiposity: Fat depositions in the crest of the neck, around the tailhead, in the sheath or mammary area, above the eyes and behind the shoulders and withers.
  • Laminitis that is often chronic and seen associated with high sugar meals and the increased sugar content in the grass each spring and fall.
  • Decreased fertility, prolonged winter anestrus and increased early embryonic loss.
  • Early onset of Cushing’s Disease, normally seen in horses older than 20 years, horses with EMS can develop Cushing’s Disease as early as 10 years of age.


EMS is a complex of problems stemming from several causes:

  • Genetic predisposition. Certain breeds (all ponies, Morgans, warmbloods, TWH, Arabians, Paso Finos, Fjords and more) are genetically programed to become obese easily and have difficulty maintaining a normal weight without strict diet and exercise.
  • Overfeed and Underworking. We tend to overestimate the amount of work our horses truly do and many times a herd-feeding mentality means we are not feeding the individual horse leading to excessive calories for some.
  • Feeding grains that are too high in sugar and starch. Sugar and starch cannot be properly digested in large quantities and lead to spikes in insulin and glucose levels that lead to obesity and insulin resistance. Traditional horse feeds like corn and oats are extremely high in sugar/starch compared to the newer formulated feeds that provide the right amount of nutrients with lower levels of sugars.


Some cases of EMS can be diagnosed based on physical appearance and history of laminitis. However it should be our aim to diagnose and treat these cases before they become so severe that they are showing signs of the devastating complications. Diagnostics that can be performed by your veterinarian include:

  • Fasting levels of insulin and glucose. A simple blood test taken after a short fast.
  • Oral Sugar Test measuring the insulin and glucose response to an oral dose of sugar (Karo syrup).
  • Combined Glucose-Insulin Test; monitoring the blood insulin and glucose levels after an intravenous dose of dextrose and insulin. This test runs the risk of causing mild hypoglycemia and should only be performed if a veterinarian can be present for the entire test (~2hours). Mainly reserved for use in clinics and for research.


The mainstay of treatment includes diet and exercise. Medications are available but should be reserved for the very severe cases that do not respond to diet and exercise alone.

  • Limit or eliminate access to pasture. Place on a dry lot or use a grazing muzzle to limit the intake of sugary grass.
  • Feed grass hay only. Alfalfa is very high in sugar.
  • Only feed a formulated grain that is low in sugar/starch that provides a balance of vitamins and minerals while being low in calories and sugar.
  • Institute an exercise program with the help of your veterinarian. Slowly increase work as your horse becomes more fit. Horses experiencing episodes of laminitis should not be exercised, making dietary changes all the more important.
  • Levothyroxine (Thyro-L) is a thyroid hormone supplementation that increases metabolism and helps aid in weight loss and reversal of insulin resistance. It should only be used in severe cases and must be used in combination with diet and exercise. Treatment should only continue until optimum weight is achieved, then the horse should be weaned off the medication and maintained on a controlled diet and exercise protocol.


With hard work and diligence on the part of the owner and the horse, obesity can be reversed and insulin resistance corrected. While these horses can be “cured” they will remain prone to obesity and could develop EMS again. It is important that once these horses return to normal that their diet and exercise regime is monitored closely throughout their lives.