Equine Metabolic Syndrome (EMS)








Equine metabolic syndrome (EMS)








What is Equine Metabolic Syndrome?


Equine metabolic syndrome (EMS) has recently been defined as a syndrome of obesity, insulin resistance and laminitis.  

Essentially EMS may be defined as “a collection of risk factors that are associated with an increased susceptibility to laminitis”.

EMS usually affects young to middle aged horses and is more common in native pony-type breeds. A horse with EMS is typically a “good doer”, i.e. easily becomes  obese and seems to gain weight on very little food intake. 

Obesity is one of the predisposing factors for development of insulin resistance; however, some of the native ponies can develop insulin resistance without being obese (there is likely to be an underlying genetic predisposition). 



What is Insulin Resistance?

Insulin resistance is a reduction of the horse’s ability to respond appropriately to the hormone insulin. Insulin is involved in the uptake of glucose from the bloodstream following eating and it’s storage in cells; therefore, with insulin resistance this very important mechanism no longer functions properly. The body tries to counteract its own insensitivity to insulin by producing more and more insulin, and it is this elevated level of insulin that tells us that insulin resistance is occurring.  

Obesity, as a direct result of excessive calorie intake, is the primary cause of insulin resistance in horses (as with people). It is now known that fat cells can produce a wide range of hormones and inflammatory mediators. These hormones down-regulate the sensitivity of tissues to insulin, which is a normal body function. However, if they are produced by larger than normal deposits of fat, their down-regulatory action is too much for the body to cope with and insulin resistance occurs. The excessive production of inflammatory mediators by the fat tissue also leads to a constant state of low grade inflammation. 


Clinical aspects include:


  • Laminitis (ranging in severity from a predisposition to seasonal episodes, to the development of laminitic rings to persistently recurrent painfullaminitis despite good management and veterinary care)

  • Obesity (this can be only “regional obesity” rather than generalised obesity, e.g. deposits of fat in the neck (“crest”) and base of the tail is widely recognised phenotype of laminitis-prone individuals)



A “cresty neck score” was proposed, which found that scores >3/5 were associated with Insulin Resistance and risk of laminitis:





The disease is essentially one that has developed from adaptation to the seasonal diet of naturally pastured horse with the ability to store fat during the summer months and survive a very poor plane of nutrition during the winter months. Ponies now have access to far more calories that they were designed to cope with due to the improved pastures they now graze on, haylage and feeding of concentrates. 

  • The earliest spectrum of insulin resistance occurs when the horse becomes overly obese and/or insulin resistant during the summer months and this result in seasonal hyperinsulinaemia and risk of summer pasture-associated laminitis (this has also been called “pre-laminitic metabolic syndrome or PLMS”)
  • The other end of the spectrum is where insulin resistance and hyperinsulinaemia are present year round and not dependent on access to lush summer pastures and laminitis can occur at any time of the year. 



How is EMS diagnosed?


  • Your vet can make provisional diagnosis after clinical examination and collecting history (in particular looking at risk factors for laminitis and obesity – e.g. diet, exercise, body condition scoring and other assessments of body fat and its distribution); however, it’s not always possible to clinically distinguish Equine Metabolic Syndrome from Equine Cushing Syndrome, so further testing is usually necessary

  • To reach definite diagnosis of EMS it is necessary to do blood test to confirm insulin resistance:

1. Baseline serum insulin (high serum insulin is strongly suggestive of Insulin resistance and further testing is usually not necessary)


2. Dynamic testing for insulin resistance – this is necessary in cases where the baseline serum insulin is only slightly elevated (‘grey zone’) or in the cases where the EMS is suspected, but the baseline serum insulin is within the normal range. For this test, the horse is fasted overnight (12 hours), then it is fed chaff with 1g/kg bodyweight dextrose powder in the morning, and the blood test is taken 2 hours later. The horses that suffer with EMS will have abnormally high insulin. 


3. ACTH test or Dynamic dexamethasone suppression test may be performed to rule out Equine Cushing Syndrome (especially in older horses that have clinical signs consistent with ECS, e.g. hirsutism) 


  • Assessment of laminitis with radiographs is important part of clinical evaluation (please see article about laminitis for further information)


Treatment and management of EMS:


Management of EMS involves management of the underlying metabolic disorder of insulin resistance and management of laminitis. Detection, monitoring of and reduction of the obesity is a major aim:



  • Dietary management involves reduction of total caloric intake as well as the non-structural carbohydrate intake. Mild cases of seasonal laminitis may only require seasonal pasture restriction, while severe cases of EMS may require a strict weight loss programme
  • In all cases, the first step is to remove all grain-based concentrates from the diet (including treats!)
  • Feeds containing high non-structural carbohydrates have been shown to induce more insulin resistance than other feeds in horses. Pastures can be very high in non-structural carbohydrates, especially spring pastures, and even when dried into hay or haylage can still be very high. Pasture access restriction is usually required. 
  • Soaking hay has been shown to reduce the starch and sugar content. Regardless of the soaking time, there is always a loss of calories from the hay; however the longer the leaching time the greater the loss and 12 hours is often recommended so that the owner can still feed up to 2.5% bodyweight to minimise the welfare consequences of reduced dry matter intake. 
  • To calculate the amount of total forage fed to induce weight loss in an obese horse, the initial aim is to feed 1.5% of the horse’s body weight. If this is insufficient this can be reduced to 1% of bodyweight, however this should be monitored carefully. With severe feed restriction some horses may develop behavioural changes.
  • It is important to ensure the horse has adequate protein, vitamin and minerals as a forage-only diet, especially with soaked forage, will not provide adequate amounts of these nutrients. A low calorie commercial ration balancer will need to be also fed (e.g. Dodson & Horrell Ultimate Balancer).


  • Exercise is extremely important in managing EMS as it helps to improve insulin sensitivity and reduce hyperinsulinaemia, and it helps reduce weight in obese horses
  • Your vet/farrier will advise you when the hoof lamellae are strong enough to withstand exercise – do not force your horse to exercise in early stages of laminitis!!
  • Exercise can be commenced on a soft surface, ideally sand school, and gradually increased with close monitoring for worsening of lameness
  • Exercise intensity does not have to be high, but the aim is for consistent exercise of 30 minutes or more daily once the hooves are stable

Medical therapy

  • Medication, such as Metformin are prescribed in some cases of EMS with the hope to increase insulin sensitivity; however,  there have been mixed results seen and the response to this medication is very individual

Copyright. East Kent Equine Ltd. 2014