Equine Metabolic Syndrome 

What is Equine Metabolic Syndrome?  

Equine Metabolic Syndrome (EMS) is a hormonal disorder in horses which is characterised by obesity, insulin dysregulation, and laminitis.  

What causes EMS? 

Both the horse’s genetics and their environment can cause EMS, as the biggest risk factor in developing it is obesity. Horses at risk of obesity may have a predisposition due to their breeding and genetics but obesity is also influenced by the horse’s environment and provision of a suitable diet. To find out more about managing horse’s weight and how obesity can affect horses, please see our Weight: Is your horse the right weight? Advice page.  

It is worth noting, horse’s who aren’t overweight, have high fat scores or have any signs of insulin dysregulation can develop EMS. For native breeds or for horses at greater risk, insulin testing is a valuable tool to assess the risk of a horse developing laminitis and EMS. The results will help owners and those caring for horses take appropriate early action to prevent either condition.

Insulin is the hormone responsible for removing glucose from the horse’s bloodstream to store it as energy for later use.  Horses with substantial fat deposits (e.g., those with a fat score of 4 to 5 out of 5) are more likely to suffer from insulin dysregulation because other hormones released by the fat lead to more insulin being produced than the horse needs. This is known as hyperinsulinemia and it is linked to higher risk of the horse developing laminitis, although the exact mechanism has not yet been identified. 

Become a member and get insured

World Horse Welfare membership with insurance gives you peace of mind for the horses you love while helping the world’s most vulnerable horses. Join today

What are the signs of EMS?  

Typical signs that a horse has EMS include: 

• Excess weight (a body condition/fat score of 4 or more out of 5) 
• Abnormal fat deposits (e.g., pockets/bulges/pads of fat around the crest, behind shoulder, at the tailhead, above the eyes, around the sheath or mammary glands) 
• Resistance to losing weight despite appropriate diet and exercise 
• Lethargy
• Current or history of laminitis 
• Infertility in mares 
• High insulin levels (determined by a blood test)  

What are the treatments for EMS?  

Weight loss is the primary treatment for EMS. This includes feeding a high fibre, forage- based diet. To feed for weight loss, it’s recommended to feed 1.5% of the horse’s body weight in forage per day. This should be done under veterinary supervision, and the horse should be regularly weighed and fat scored to track progress.  

There are now pharmaceutical options for promoting weight loss such as the use of ertugliflozin.  Whilst the risk of side effects is very low, these drugs are not without risk and should only be used in horses where the risks of laminitis outweigh any risk of using the drugs and/or where diet and management change have been insufficient to control EMS. Please speak to your vet for more information.

Regular exercise is another key element of a weight loss programme and can include increasing the time spent moving and walking for those requiring lower intensity exercise, up to higher intensity exercise as the horse’s fitness improves.  

We have a dedicated advice page all about weight management strategies for overweight horses, if you’d like more information on safely managing your horse’s weight loss. 

Equine Metabolic Syndrome Fast Facts 

This fast facts guide includes further information on:  

• Risk factors and management of EMS 
• When to call the vet and treatment of EMS 

Download PDF