Equine Metabolic Syndrome

Kaela Schraer, DVM
By Kaela Schraer, DVM on Feb. 16, 2023
Overweight horse

In This Article


What is Equine Metabolic Syndrome?

Equine Metabolic Syndrome (EMS) is one of the top reasons veterinarians are such big sticklers when it comes to a horse’s weight. EMS is a common condition in horses, especially among Quarter Horses, Morgans, Arabs, ponies, and donkeys.

Similar to diabetes in humans, horses with EMS process insulin incorrectly and this leads to problems with their metabolism. Excessive weight is both a key symptom of EMS as well as a compounding factor that can make the disease worse. It is often first diagnosed in young to middle-aged horses.

Symptoms of Equine Metabolic Syndrome

  • Obesity/high body condition score

  • Difficulty losing weight

  • Gaining weight easily

  • Regional adiposity (fatty deposits in specific areas such as the crest of the neck and tail head)

  • Laminitis

Causes of Equine Metabolic Syndrome

The exact underlying cause of EMS is unknown but researchers have found there is at least some genetic component since certain breeds seem to be much more predisposed to it.

How Veterinarians Diagnose Equine Metabolic Syndrome

Any diagnosis of EMS will start with a thorough history and physical exam by your veterinarian. They will estimate your horse’s body condition score and look for evidence of regional adiposity. If your horse has been lame, they will try to determine if they are experiencing laminitis. To do this, they will check to see if they have soreness or heat in their feet or bounding pulses in their pasterns.

If veterinarians are suspicious of EMS, the next step is usually bloodwork. They can check baseline blood glucose and insulin levels as screening tests for the disease. These tests can often result in false positives and negatives depending on a horse’s stress level or if they just ate a large meal. This is typically used a starting point to help guide further diagnostics.

The gold standard blood test for EMS is an oral sugar test. This test involves taking a blood sample prior to giving your horse a high sugar syrup and then taking additional samples 60 and 90 minutes after. This test shows how well the horse’s insulin responds to glucose in the blood before returning back to normal.

Additionally, your veterinarian may want to test for other conditions that can make EMS harder to treat including hypothyroidism and Equine Cushing’s Syndrome (PPID).

Treatment of Equine Metabolic Syndrome

The most important part of treating EMS is diet. It is important to decrease both the calories (if your horse is overweight) as well as the non-structural carbohydrates (NSCs). NSCs come from three main components of a horse’s diet: grain/pelleted feed, hay/roughage, and grass. Each of these sources will need to be adjusted to get the best results when managing a horse with EMS.

  • Grain/pelleted feed: Choose a low carb grain or even switch to a ration balancer.

  • Hay/roughage: Have a hay analysis performed and moving forward use only hay that has the lowest NSC content.

    • You can also soak the hay in water for at least half an hour to remove some of the sugars. This method is less ideal because it also removes other key nutrients that horses need, and these will need to be replaced through a ration balancer or other supplement.

  • Grass: It can be very hard to manage the amount a horse is eating when they are turned out. Decreasing the amount of time your horse is turned out may not be enough. Using a grazing muzzle in addition to limiting the time your horse is out, or turning your horse out in a dry paddock without grass is often required for managing a horse with EMS.

If your horse loses too much weight on their diet, your veterinarian will likely recommend putting the weight back on through fat sources such as vegetable oil, coco soya oil, or fat supplements, because these are safer than carbohydrates for horses with EMS.

If your horse is not having an active episode of laminitis, then exercise is also recommended. Exercise is extremely important because it can help increase the horse’s insulin sensitivity and decrease the effects of EMS.

Additional treatments may be recommended by your veterinarian especially if they have concurrent conditions such as hypothyroidism or PPID that can worsen EMS.

Recovery and Management of Equine Metabolic Syndrome

EMS is a lifelong condition. The symptoms can be managed but there is no cure. It will be important to maintain your horse at a healthy body condition and keep them on a low NSC diet for their entire life. Keeping them in a consistent exercise program can be very beneficial as well.

It will be important to have regular visits with your veterinarian to make sure that the diet your horse is on is still appropriate and to monitor for concurrent conditions like hypothyroidism, PPID, and laminitis.

Equine Metabolic Syndrome FAQs

What are the most common signs of EMS?

  • Obesity

  • Difficulty losing weight

  • Easy keeper (gains weight easily)

  • Cresty neck (regional adiposity)


Morgan, R et al. Equine metabolic syndrome. The Veterinary record vol. 177,7 (2015): 173-9. doi:10.1136/vr.103226

Young, A. UC Davis School of Veterinary Medicine. Equine metabolic syndrome. 2020.

Featured Image: iStock.com/MelissaAnneGalleries


Kaela Schraer, DVM


Kaela Schraer, DVM


Dr. Kaela Schraer graduated from Tufts Cummings School of Veterinary Medicine in 2017 with her doctorate in veterinary medicine. After...

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