Equine Metabolic Syndrome or ‘EMS’ is a hot topic amongst horse owners and scientists alike. However, as there is no widely accepted definition of, or set of criteria for diagnosing EMS, many researchers believe it is a condition that is still open to misinterpretation. In this blog, we set out some of the current thinking on EMS, alleviate some of the misunderstandings and share our latest research as we strive to improve our understanding of this condition…



What is EMS?

The term EMS was first introduced by Johnson (2002) after similarities were seen between horses at risk of laminitis and the human ‘metabolic syndrome’ which describes a collection of risk factors for type 2 diabetes and cardiovascular disease. Initially, EMS was defined as the combination of obesity or regional fat depots, current or previous laminitis and insulin resistance. As research continues, the definition of EMS has continued to evolve and today can perhaps be best described as being a collection of risk factors associated with an increased risk of laminitis including ‘insulin dysregulation’ (as opposed to insulin resistance). Although affected horses are typically overweight/ obese, EMS also occurs in lean or underweight horses.


Insulin dysregulation (ID)

Insulin is a hormone produced by the pancreas. The release of insulin, signals cells, especially in the muscle and liver to absorb glucose from the blood. The exact link between abnormalities in insulin regulation and laminitis remains unclear.  A high level of insulin in the blood (hyperinsulinemia) may or may not be accompanied by insulin resistance (failure of cells to respond to insulin). This is why a new term insulin dysregulation is now used and refers collectively to excessive insulin responses to sugars, fasting hyperinsulinaemia and insulin resistance, which are all components of equine metabolic syndrome.


EMS is not the same as diabetes!

Although diabetes mellitus (type 2 diabetes) may occur as a complication of EMS, it is extremely rare in horses. In cases of diabetes or ‘uncompensated insulin resistance’, the pancreas secretes insufficient levels of insulin or in some cases stops secreting completely, resulting in poor glucose regulation.  In cases of ‘compensated insulin resistance’, the most common form in horses, high levels of insulin are produced in order to compensate for reduced tissue sensitivity. As a result, insulin levels in the blood are high but blood glucose is maintained within a relatively normal range.


Good doer


How is EMS diagnosed?

Diagnosis is based on a combination of physical examination, clinical history and assessment of insulin regulation. Various tests have been recommended for diagnosing 'EMS', each of which include aspects of ID. These most commonly include:

  • The oral sugar test (OST) - the horse or pony is fasted and then given ‘Karo syrup’ by syringe. Blood samples are then taken at set time points e.g. 60 and 90 minutes later to measure glucose and insulin response (the new higher dose introduced this year does not require fasting).
  • The in-feed oral glucose test - the horse or pony is fasted overnight and then given glucose powder in a small low/ non-glycaemic feed. A blood sample is taken 2 hours later to measure glucose and insulin response.
  • The combined glucose insulin test (CGIT) – the horse or pony is fasted overnight and then given an intravenous (IV) glucose infusion followed by IV insulin infusion. Blood samples are taken at multiple time points to measure glucose and insulin response.


New research

New research published in collaboration with SPILLERS has investigated how we can improve the usefulness of  the OST and CGIT in ponies.


  • Study 1: Repeatability of the combined glucose/ insulin test in ponies of the same breed and gender, across time. The current threshold levels used in the CGIT were validated in horses so in order to evaluate whether these levels are reliable in ponies, CGIT were carried out in 6 Welsh Mountain ponies on four separate occasions. The high degree of variability within individual ponies showed that the current reference values used to diagnose insulin dysregulation need to be amended for use in ponies.


  • Study 2: Use of the oral sugar test in ponies when performed with or without prior fasting. Fasting prior to the OST is not always practical for horses and ponies living out at pasture. In this study, OST’s were performed in 10 native ponies on 4 separate occasions, 2 fasted and 2 without fasting. Fasting and non-fasting results were similar in terms of being either ‘positive’ or ‘negative’ suggesting that future OSTs could be performed in grass kept horses and ponies. However absolute results showed poor repeatability which means they should be interpreted with caution when used to confirm a diagnosis.


  • Study 3: Effect of Varying the Dose of Karo Light Syrup on the Insulin Response to the Oral Sugar Test. Previously only one dose rate of Karo syrup had been validated for use in the OST. However results of this study showed that a higher dose may be able to identify whether or not ponies have previously suffered from laminitis.

Management advice

When it comes to preventing laminitis, the best advice is to manage as many of the risk factors as possible, regardless of whether or not your pony has been diagnosed with EMS. This includes:

  • Maintaining a body condition score of 4.5-5/ 9
  • Choosing feeds low in starch and sugar
  • Feeding a low (<10% dry matter) WSC hay or a hay replacer
  • Restricting or removing grazing


Grazing Muzzle


For more advice on feeding a horse or pony with EMS contact the SPILLERS Care-Line


Morrison P.K., Dugdale A.H.A, Grove-white DH, Harris P.A., Barfoot C.F & Mcg Argo C (2017) Repeatability of the combined Glucose/insulin test in ponies of the same breed and gender, across time Journal of Equine Veterinary Science, 52, p57.

Knowles, E. J., Harris, P. A., Elliott, J., & Menzies‐Gow, N. J (2017). Use of the oral sugar test in ponies when performed with or without prior fasting. Equine Veterinary Journal 49 519 – 524.

Jocelyn N.A., Harris P.A., MEnzies Gow N.J. (2017) Effect of varying the dose of karo light syrup on the insulin response to the oral sugar test . In    the Havemeyer International Equine Endocrinology summit Florida. P30.