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Equine Metabolic Syndrome


EMS is present in horses, ponies or donkeys that have a combination of characteristics including obesity, insulin resistance, high blood pressure and genetic predisposition. Equines suffering from EMS have an imbalance of the hormones that regulate glucose in a similar way to people with type II diabetes. It can cause uncontrollable, very painful laminitis.


Typical stance of a pony suffering with laminitis

Cause: Fat is no longer thought to be just a store of energy and is now recognised as a metabolically active substance that produces hormones. Susceptible individuals that acquire too much fat and develop obesity (particularly native breeds) often go on to develop insulin resistance and are then said to have equine metabolic syndrome. The initial cause of obesity is inappropriate diet and lack of exercise.  There may be a genetic predisposition.


The scientific bit….

Obese ponies have an increase in the total number of fat cells, called adipocytes. Adipocytes produce several hormones including adipokines and cortisol which are produced in excess in obesity. Both of these hormones inhibit insulin which results in hyperglycemia (high blood sugar levels). To compensate the pancreas produces more insulin so there is actually a greater than normal amount of insulin circulating in the blood but the body is not receptive / responding to it.



  • Obesity
  • Abnormal fat distribution (crest of neck and tail head) 
  • Recurrent laminitis (see our laminitis information sheet)
  • Excessive drinking and urination
  • Abnormal cycling and infertility in mares



Equine metabolic syndrome may be strongly indicated by the presence of symptoms but the same symptoms are also seen in horses with Cushings syndrome and it is important to differentiate between the two. One important difference is that Cushings syndrome frequently occurs in older horses (usually over 10 years) where as EMS can occur at any age. 

The best way to confirm EMS is to take a fasting (starved for at least 10 hrs) blood sample and measure the levels of glucose, insulin and ACTH (adrenocorticotrophic hormone).  If a horse has EMS, the glucose and insulin will be high indicating insulin resistance. These may also be high if the horse has cushings induced insulin resistance, so ACTH can also be measured.  ACTH is abnormally high if they have Cushings disease but normal in horses with EMS. 

Like all blood tests for hormonal disease there will be a small number of horses that test negative but we are still strongly suspicious of having the disease. In such cases we would run further blood tests to try and improve the accuracy of the results. Such tests might include a glucose stimulation test which involves feeding the horse with glucose after an overnight starve, and taking a blood sample 2 hours later to measure insulin and glucose. An excessive release of insulin supports the diagnosis of EMS.

Blood tests are not just important for diagnosis but also help  to monitor the response to treatment. It is also important to remember that hormones have a huge range of effects on the body and any imbalance can upset other body systems e.g. Liver so routine blood tests should also be run.



The aims of treatment are to improve insulin sensitivity and reduce body weight by improving the horse’s diet and increasing exercise. In our experience it can be very difficult for horses with EMS to lose weight by changing the diet alone so implementing the full range of therapies is important.


  • Metformin is a drug we give to EMS sufferers to help improve insulin sensitivity, it is used in humans to help manage diabetes type II. Metformin comes in tablet formulation and is given in feed twice a day.
  • Maintain a high plain of nutrition by feeding good quality fibre (Happy-hoof or HiFi lite) but low amounts of sugars and carbohydrates to reduce laminits risk. Glycaemic feeds such as cereal, carrots and apples should be avoided. Vitamin supplementation including Vit C is advised due to reduced intake of fresh feedstuffs.


  • It is important that EMS sufferers are exercised every day for at least 30 minutes. Even if all that can be managed is lunging or leading out exercise is important for weight loss and normal utilisation of glucose. (Obviously a horse suffering from laminitis should not be exercised but kept on strict box rest until recovered).
  • Due to their high risk of laminitis fresh grass should be avoided during the day. Grazing should only be allowed on very short pasture in a confined space. Use of grazing muzzles can also help.
  • Regular use of a weighband


Candy (aged 5 years) before and after treatment for EMS