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What is Equine Metabolic Syndrome?

Equine Metabolic Syndrome (EMS) is a condition that is associated with 3 main features: obesity or regional adiposity (fat pockets on various parts of the horse’s body, such as the neck and ribs), insulin resistance or insulin regulation issues, and laminitis.


What causes EMS and where did it come from?

EMS is believed to be caused by genetic factors. Because certain breeds, such as ponies, donkeys, and Arabians are predisposed to developing EMS, some believe that gene associated with EMS was evolutionarily developed to help equines in food scarce climates be able to more efficiently store carbohydrates and maintain their weight to prevent starvation when food was not available.

However, a horse’s environment can play a factor in a prone breeds development of EMS- such as rapid pasture growth, or unregulated access to a pasture (where they may experience hyperphagia: a hunger to eat non-stop).


Regardless of the origins of EMS, it is important to know that EMS affected horses produce high levels of insulin when they eat meals that have high levels of specific carbohydrates, and these insulin levels are slow to return back to a normal level.


Laminitis and Other Affiliated Conditions

One of the largest concerns regarding EMS is that it increases a horse’s likelihood of developing laminitis, which is an extremely painful (and in severe cases, potentially life threatening) condition where an animal’s hoof separates from the underlying coffin bone. This can make it painful and difficult for your horse to walk and stand, which can restrict their mobility and access to necessary resources, such as food and water.

Horses with EMS may also be more prone to developing hyperlipemia, which is a condition where the blood stream passes too much fat to the liver, and therefore causes the liver to become diseased and function less efficiently. Hyperlipemia can cause EMS to worsen significantly, because it can affect a horse’s desire to eat, which, in turn, affects insulin levels.

In addition to laminitis and hyperlipemia, another cause for concern is the increased likelihood of developing PPID (also known as pituitary pars intermedia dysfunction- say that five times fast), obesity, and infertility.


What should I do if I think my horse has EMS?

First, talk to your vet. Your vet should be able to run blood tests that can determine the glucose and insulin levels of your horse. It is quite likely that the vet will want to come to where the horse is and take the tests there- this is because glucose levels can also be affected by other factors- such as stress, or diet changes. Keeping your horse in the place that it considers home is important for an accurate test.

If your horse tests positive for EMS, the likely methods of treatment are dietary management, non-structural carbohydrate restriction, gradual calories restriction (emphasis on the term gradual: from 1.5% of their body weight to 1.25%, and then after some time, down to 1% until they reach their ideal body weight- this is important because sudden restrictions can worsen EMS), eliminating/restricting pasture access, increasing exercise, and if all else fails, possible Thyroxine or Metformin supplementation. Non-structural carbohydrate restriction may come in multiple forms: the preferred method is to run a feed analysis so that your vet can have an in-depth understanding of your horse’s current nutrient intake.

If a feed analysis is not a good option for you and your horse, they may suggest soaking your horse’s hay, which will lower the levels of non-structural carbohydrates. Should you choose this option, please know that is important to add vitamin and mineral supplements because the soaking process can also leech much of the nutritional value in hay.


Kritchevsky, Janice. (2019, April). Overview of Equine Metabolic Syndrome. Merck Veterinary Manual.

Young, Amy. (2020, March 23). Equine Metabolic Syndrome. UC Davis Veterinary Medicine Center for Equine Health.

University of Minnesota College of Veterinary Medicine: Leatherdale Equine Center. Equine Metabolic Syndrome.

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