For horse owners and barn managers, Equine Metabolic Syndrome (EMS) is a challenging condition to manage. How do you know which hays and feeds are safe and how should pasture turnout be regulated?

Horses and ponies diagnosed with EMS cannot effectively metabolize dietary sugars due to a reduced insulin sensitivity. These horses are often overweight or obese and have an increased risk of laminitis.

Metabolic horses need to be fed a diet with reduced sugars and starches. It’s also important to manage their weight and regulate caloric intake while balancing vitamins and minerals.

Proper dietary management is key to helping horses with EMS live long and happy lives and reducing the risk of laminitis or other complications.

If your horse has been diagnosed with EMS, work with the equine nutritionists at Mad Barn to create a personalized feeding plan that supports metabolic health.

What is Equine Metabolic Syndrome

Equine Metabolic Syndrome is a common condition affecting horses of many breeds. The American College of Veterinary Internal Medicine describes the EMS horse as having: [1]

  • Increased fat deposition throughout (obesity) or in specific locations (e.g. cresty neck)
  • Abnormal insulinemic or glycemic responses to a glucose test (oral or IV)
  • Laminitis (clinical or subclinical) that has developed without a recognized cause

Equine Metabolic Syndrome is not considered a disease, but rather a metabolic type associated with an increased risk for the development of laminitis.


EMS is a complex syndrome that involves insulin resistance and oxidative stress. [2][3]

Horses diagnosed with EMS may also have elevated triglycerides or leptin in the blood. [1]

The overt systemic inflammation observed in human metabolic syndrome is not consistently found in equine studies. [29][30]

Insulin Resistance

Insulin resistance describes an impaired cellular response to the hormone insulin. This hormone is secreted by the pancreas when blood sugar (glucose) is high. Blood sugar levels rise after a meal, particularly when there is high sugar and starch content in the diet.

Insulin helps lower blood glucose by stimulating cells of the liver, muscle, and adipose (fat tissue) to take in glucose from the blood. In a normal horse, blood glucose levels will return to normal by two hours after a meal.

In horses with insulin resistance, the cells of the liver, muscle, and adipose don’t respond well to insulin. Glucose may rise higher and stay elevated in the blood for longer which triggers further insulin secretion.

Horses with EMS have high levels of circulating insulin (hyperinsulinemia) and rarely have elevated sugars (hyperglycemia).


Although not the cause for the development of EMS, obesity is common in horses diagnosed with EMS and contributes to reduced insulin sensitivity.

However, some horses with EMS might appear normal without general or regional fat deposition. [1]


EMS is most commonly observed in obese and senior horses. However, signs of metabolic syndrome such as easy weight gain can begin to appear once the animal has stopped growing.

An estimated 18 – 27% of horses and ponies have insulin resistance, and up to 51% of horses in the United States are considered obese. [4]

Your horse’s risk of equine metabolic syndrome is affected by genetics (breed), diet and exercise level. Careful attention to diet and exercise can help reduce their risk even if they are genetically predisposed to developing EMS.

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How to Feed a Horse with EMS

The first step to managing and treating a horse newly diagnosed with EMS is to make changes to their feeding program.

The diet of an EMS horse should focus on: [5]

  • Reducing sugar and starch intake
  • Paying close attention to calorie supply
  • Providing sufficient but not excess protein
  • Meeting their vitamin and mineral requirements

The overall goal is to achieve or maintain a healthy body condition while providing a well-balanced, low HC diet.

The best way to meet this goal is to feed a forage-based diet that consists of hay that is low in starch and sugar.

Limiting pasture intake and removing high-HC grains and concentrate feeds may also be necessary.

In addition to diet, horses affected by EMS may benefit from regular exercise or medication to improve their body condition and insulin sensitivity. [6][7]

1. Reduce HC intake

Parts of NSC (non-structural carbohydrates) represent components of the diet that trigger insulin secretion. NSC is a combination of sugars, fructans and starch.

Fructans are storage carbohydrates in plants and do not cause a rise in blood sugar. The plant components of interest are ethanol-soluble carbohydrates (ESC – simple sugars) and starch. In physiological terms, these are the hydrolyzable carbohydrates (HC).

On a forage analysis, the NSC can be calculated as WSC plus starch. Hydrolyzable carbohydrates are calculated as ESC plus starch.

If your horse has EMS, it is important to know the HC content of their ration. Some feed tags show this value clearly on the guaranteed analysis, but many feeds do not include this information.

A feed that is high in cereal grain products, such as ground wheat, is likely to have a high NSC and HC content.

The first step to reducing HC content is to remove complete feeds and grains. Avoid any sweet feeds or products that contain molasses. Even some ration balancers may have inappropriately high HC.

2. Choose an Appropriate Hay

All horses and ponies should be kept on a forage-based feeding program. Because forage represents the bulk of the diet, it is important to choose low-HC hay for your EMS horse.

The only way to know the HC and energy content of hay is to obtain a hay analysis. Ideally, the HC content (ESC + starch) of the hay should be no greater than 10% on a dry matter basis. [8]

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Type of Hay

Typically, grass hay cut at a mature growth stage will have lower energy and HC content than young grass. Look for grass hay such as timothy or orchardgrass that has relatively rigid stems and seedheads showing.

Because alfalfa hay tends to be energy-dense, it is not recommended for EMS horses. Anecdotally, some horses with EMS may experience laminitis when fed alfalfa, although the reason is unclear.


Although mature grass hay is preferred, you may be in a situation where early growth hay that is high in calories and HC is the only forage available. In such cases, mixing in straw chopped straw can dilute the energy and HC content of the total diet.

There are several considerations with feeding straw:

  • Ensure the straw has no seedheads present as these will contain high levels of starch.
  • Monitor your horse’s foraging behaviour to ensure they are eating the straw and make adjustments if they are selectively avoiding it
  • Ensure protein requirements are still met

Amount of Hay

Mature grass hay is ideal for supporting insulin sensitivity and weight loss while maintaining appropriate hay intake.

For many horses with EMS, free choice access to hay usually leads to excess intake as their appetite may be dysregulated. [4]

Restricted forage access may be necessary to support weight loss and insulin sensitivity. It is commonly recommended to restrict forage to 1.5% of body weight. For a 500 kg, 1100 lb horse this equates 7.5 kg (16.5 lb) of hay dry matter. Once the horse has reached target weight, you can try feeding 2% of that body weight.

Consider Soaking the Hay

If your horse’s forage hay has not been tested or is high in ESC and total HC, soaking the hay is recommended to reduce sugar content. Hay can be soaked for 30 minutes in warm water or 1 hour in cold water.

Soaking hay can reduce sugar content by up to 50%, resulting in lower glycemic and insulinemic responses post-consumption. Soaking will also reduce the energy content of the hay, which will help support weight loss and weight management. [9]

3. Reduce or Eliminate Pasture Intake

Although horses and ponies should be kept on a forage-based program, restricting their pasture intake is recommended to reduce the risk of pasture-associated laminitis and to promote weight loss.

Pasture grass can be very high in sugar, especially when the grass is young and growing (i.e. in the Spring) or has been exposed to frost. [10] Besides putting the horse at risk of laminitis, high sugar intake also contributes to weight gain.

If the horse cannot be turned out in a dry lot, pasture intake can be limited through the use of a grazing muzzle. A grazing muzzle can reduce pasture intake by up to 80%. [11][12] Some muzzles can be completely sealed off to grass but still allow water intake

Turning your horse out at night may also be an option, as the sugar content in grass tends to be lower through the night than during the day. [13] Sugar peaks in late afternoon, drops overnight and is lowest just before dawn. [32]

Pastures that are allowed to grow to full height and drop their seed have the lowest HC content. [33]

4. Carefully Choose Grains and Concentrate Feeds

To reduce HC and energy intake, remove grain and concentrates from the diet. Most grains and concentrate feeds are high in HC and are not the best choice when feeding an EMS horse.

Complete feeds may also contain supplemental fat, which is calorie dense and should be avoided for overweight horses.

If your horse has higher energy demands, grass hay pellets or cubes may be added. Pay careful attention to their nutritional analysis to ensure they have a safe level of starch and sugar.

Many other low HC feeds are appropriate for adding energy to the EMS horse’s diet. Choose fermentable fiber sources or fat supplements, such as:

5. Provide Vitamins and Minerals

Forages alone will not meet all your horses vitamin and mineral requirements.

Vitamins and minerals are key micronutrients that support enzyme function and metabolic processes, such as sugar and fat metabolism. These nutrients are also involved in antioxidant processes, which protect against oxidative stress and inflammation. [14][15]

Some examples of vitamins and minerals critical for metabolic health include: [16][17][18][19][20]

  • Zinc, Copper & Manganese: Required for the antioxidant enzyme superoxide dismutase
  • Selenium: Required for the antioxidant glutathione
  • Magnesium: Supports insulin signaling
  • Chromium: Supports insulin signaling, provide anti-inflammatory and antioxidant benefits
  • Vitamin E: Potent anti-oxidant

When choosing a vitamin and mineral supplement for EMS horses, concentrated products with a low feeding rate are more appropriate than complete feeds or ration balancers.

Mad Barn’s AminoTrace+ is a vitamin and mineral specifically formulated to meet the nutritional needs of horses with EMS, insulin resistance, and/or laminitis by addressing the most commonly seen excesses and deficiencies. This low-HC formula contains organic trcace minerals with high bioavailability and high levels of magnesium and chromium.


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  • Complete mineral balance
  • Supports metabolic health
  • Formulated for IR/Cushing's
  • Hoof growth

Additional Dietary Considerations

Feeding your EMS horse a well-balanced forage-based diet with low HC content is the best way to support their health.

However, additional supplements may also be warranted and are supported by research studies in horses and other animals.

Treats for Metabolic Horses

Treats high in sugar should be removed from the diet to support weight loss. Avoid molasses-rich commercial treats, fruits, vegetables and grain.

However, if treats are needed as part of your training program, grass hay pellets or peanuts (in shell) are appropriate and convenient for EMS horses and ponies.

There are also many low NSC commercial treats on the market which may be appropriate.

Omega-3 Fatty Acids

Although not as extensively researched in horses, omega-3 fatty acids are often recommended for humans with metabolic dysfunction. Omega-3s are believed to reduce overall inflammation and improve insulin sensitivity. [21][22]

A pilot study involving 10 EMS horses found that 16 g per day of the omega-3, docosahexanoic acid (DHA), decreased the insulin response to an oral glucose test, as compared to the horses that were not supplemented.

The DHA supplement also appeared to reduce inflammation, lower serum triglycerides, and improve several markers of metabolic health. [23]

DHA is not found in plant oils but can be found in high concentrations in fish oil or algae. Mad Barn’s w-3 oil contains microalgae, which provides DHA without a fishy smell. This makes W-3 oil a palatable source of DHA for horses.

w-3 Oil

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  • Promotes joint comfort
  • Helps to fight inflammation
  • Skin & coat condition
  • Palatable source of Omega-3's

However, feeding any oil introduces additional calories to the diet. Consult with an equine nutritionist to help you determine how much omega-3 to feed to your EMS horse.

Additional Supplements

Many herbal supplements are purported to support metabolic health. While some have limited research in horses, many rely on research in animal models and humans to provide evidence of beneficial effects.

Some supplement ingredients commonly fed to horses with EMS and their suggested effects include: [24][25]

  • Milk thistle: provide antioxidants, support liver function
  • Chasteberry: alter hormone levels, may benefit horses with Cushing’s / PPID. However, note that this herb may interfere with pergolide. [31]
  • Turmeric: normalize blood sugar, enhance insulin sensitivity
  • Aloe vera: may slow carbohydrate absorption
  • CoQ10: antioxidant, supports mitochondrial function
  • Lipoic acid: supports mitochondrial function

Feeding to Support Weight Loss

Weight management is a very important consideration for improving the overall health and quality of life of EMS horses.

Healthy weight loss will support metabolic function by improving insulin sensitivity and overall glycemic response. [26] Strategies for supporting weight loss include: [8][27]

Rationing the Hay

Offer between 1.5-2% of your horse’s body weight in hay, depending on the energy density of your hay.

Weighing the Hay

Not all flakes of hay are the same. Weighing your hay will help you accurately feed a precise quantity.

Soaking the Hay

Reducing the sugar content of the hay by soaking will also reduce its energy content.

Removing Concentrate Feeds and Grain

Concentrates and grain-based feeds tend to be energy dense. Removing these will reduce excess energy in the diet so your horse is not exceeding their calorie requirements.

Increasing exercise

Aim for light to moderate exercise of at least 30 minutes five times per week (or as much as possible) to encourage weight loss and improve insulin sensitivity. Short bouts of intense exercise can also improve insulin response.

Using a Hay Net

You can consider using two hay nets (i.e. doubling up) to increase feeding time by minimizing mesh size. There are also very small mesh hay nets available. Using a hay net will ensure your horse eats an appropriate amount of hay while avoiding behavioural issues associated with restricting hay.

Feeding Chopped Straw

If you need to dilute high-quality hay, consider mixing it with chopped straw (chaff) to reduce the overall energy content of the forage.

Monitoring Body Condition

After balancing the diet to support weight loss, monitor your horse’s progress regularly. Ideally, record your horse’s body weight and body condition score weekly. [28]

This will help you track whether your horse is losing weight over time so you can determine if further changes are needed to their feeding program.

Aim for a body condition score (BCS) of 5 out of 9 and a weekly rate of weight loss between 0.5 – 1% of the horse’s body weight. [8][27]


In addition to regular exercise, metabolic horses require an appropriate diet to support insulin sensitivity and weight loss.

An optimal feeding program will reduce the risk of laminitis and improve the overall health and quality of life in horses diagnosed with EMS.

Submit your horse’s diet for a free analysis from Mad Barn’s team of qualified equine nutritionists. Our nutritionists will work with you to create a well-balanced, forage-based diet tailored to the needs of your horse or pony diagnosed with EMS.

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  3. Marycz, K. et al. Excessive Endoplasmic Reticulum Stress Correlates with Impaired Mitochondrial Dynamics, Mitophagy and Apoptosis, in Liver and Adipose Tissue, but Not in Muscles in EMS Horses. Int J Mol Sci. 2018.
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