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Equine Metabolic Syndrome (EMS)

Equine Metabolic Syndrome (EMS) is a hormonal disorder similar to Type 2 diabetes in humans.

  • Last reviewed: 28th June 2022
Horses Heads In Stable Shutterstock 64999777 Horses Heads In Stable Shutterstock 64999777

Any horse or pony is at risk, although it is seen much more often in overweight animals, as obesity is the main known risk factor for EMS1. The main disorder of EMS is insulin resistance, and as a consequence, this puts the horse at risk of laminitis and many other complex disorders2.

Advice specific for donkeys is available from The Donkey Sanctuary.


  • One of the most common signs of EMS is the development of abnormal fat deposits (pockets/bulges/pads), usually seen around the crest, behind the shoulder, the hind quarters (especially at the tail head) and above the eyes.
  • Difficulty losing weight
  • Recurring episodes of acute laminitis
  • Increased drinking and urination
  • Lethargy (lack of energy)
  • EMS has been associated with infertility in mares3.
The role of Insulin

Insulin is a hormone and has an important task of regulating glucose (sugar) metabolism. Glucose is taken from the bloodstream to be used as fuel (for example movement of muscles) or stored as fat. Therefore, insulin plays a major part in regulating blood sugar levels.

However, problems occur when hormones produced by excessive fat cells prevent insulin from carrying out its vital task, leading to insulin resistance and elevated blood sugar levels. The body responds and starts to compensate by producing more insulin which ends up circulating in the horse’s bloodstream. This is known as hyperinsulinemia. 

It is because of these hormonal changes that EMS is commonly linked to causing laminitis, although the exact mechanisms of how this happens is not yet fully understood2

Blue Cross Pony
Photo credit: Blue Cross


Diagnosis and management of EMS before laminitis develops is key to preventing chronic, recurrent laminitis.

As well as looking out for the clinical signs, blood testing is another way of diagnosing EMS in your horse. Samples will generally be taken to measure the levels of insulin and glucose in the bloodstream2. If high levels of both substances are detected, this is a clear sign of EMS.

If you suspect your horse is suffering with EMS, speak to your vet for further guidance on diagnostic testing.


The good news is that EMS can be reversed. Due to the complex nature of EMS, there is likely to be weight loss resistance. For horse owners this can be disheartening so it is vital to seek the support of your vet, nutritionist, and if you have lessons, a BHS Accredited Professional Coach, to help tailor an individual plan to meet the specific needs of your horse.

Reducing calorie intake and increasing physical activity are key to reducing weight and improving insulin sensitivity1,2, which is a primary goal in the treatment for EMS. Exercise significantly improves the uptake of glucose by muscles and decreases blood sugar levels.

However, exercise can be limited in horses with EMS if they have acute or chronic active laminitis. Ideally, as soon as the horse is comfortable and with veterinary advice, a controlled exercise programme may begin. The exercise should be tailored to the individual horse, taking into account their level of fitness, current condition, age and the facilities available to you. See our advice on horse health and fitness.

A variety of medications and supplements are also available for horses suffering with EMS – seek veterinary advice.


EMS is a complicated disorder and any horse or pony, regardless of their weight, can be affected. However, the condition is seen much more frequently in overweight animals, meaning the risk of developing EMS significantly increases if your horse is overweight or obese. It is therefore important to keep your horse at a healthy weight to help decrease the risk. 

Tips to keep your horse’s weight healthy

Monitor your horse’s weight

Monitor your horse’s weight closely and react to any changes. Use a weigh tape and get hands-on by fat scoring (body condition scoring). 


Don’t keep an overweight horse unnecessarily rugged through winter as this time of year can be used as an advantage to help the horse lose weight. Instead of un-used calories being laid down as excess fat, the horse can use the calories to keep warm.

Learn how your horse naturally keeps warm and find information on to rug or not to rug.

Fewer calories

Weighing your forage and feed, according to what your vet or nutritionist has advised, allows you to know exactly what your horse needs and limits the intake of any unnecessary calories!

Get your forage analysed so you know exactly what calories your horse is eating and consider soaking your hay to reduce the calorie content further. Recommendations for how long you should soak hay for varies, but ideally it should be soaked for at least six hours in cold water although less time may be needed in warmer weather4. You may also consider feeding a lower calorie forage. Feeding your horse 50% hay and 50% barley straw will contribute to weight loss5. However, always make these changes gradually and ensure your horse’s teeth are in good shape  before introducing straw as it does take more chewing - this will also reduce the risk of colic.

Restricting grazing

Grass is a major contributor of calories in a horse’s diet. Grazing can be restricted by using electric fencing to strip graze, setting up a track system or by using a grazing muzzle. 

Turning out on a woodchip paddock is ideal for a horse suffering with EMS, as their calorie intake can be tightly controlled. It is important that horses are not left for long periods of time without food, and they should never be starved. Such actions could lead to a serious condition called hyperlipemia. It is very important that a food management plan is produced in partnership with your vet or nutritionist.

Get your horse moving

Exercise programmes should be built up gradually and even if your horse cannot be ridden, taking them on a daily walk in-hand can be a great form of exercise and helps keep them active. If you struggle with time constraints, buddying up can be an effective way to give your horse more time for exercise, whilst also providing a support mechanism.

Learn more about safely developing your horse's fitness.


Using enrichment helps to reduce the rate of consumption, while making feeding interesting; for example consider using trickle feeders or hay balls. This will also provide some additional movement for the horse.

Learn how to introduce enrichment safely to your horse.


1) Morgan, R. Keen. et al. (2015). Equine Metabolic Syndrome. Veterinary Record. 177(7). pp. 173-179. 

2) Durham, A, E. et al. (2019) ECEIM consensus statement on equine metabolic syndrome. Journal of Veterinary Internal Medicine. 33(2) pp. 335–349. 

3) Keen, J. (2013) Equine Metabolic Syndrome/Insulin Resistance Syndrome in Horses. John Wiley & Sons, Ltd. pp. 217-228 

4) Rendle, D. et al. (2018) Equine Obesity: current perspectives. UK Vet Equine 2(5) 

5) Dosi, al. (2020) Inducing weight loss in native ponies: is straw a viable alternative to hay? Veterinary Record 187, e60. 

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