Equine Metabolic Syndrome (EMS) and Insulin Resistance in horses.


Equine Metabolic Syndrome is a condition in horses that is characterized by Insulin Resistance (IR), obesity, and laminitis. Pituitary Pars Intermedia dysfunction (PPID), also known as Cushing’s disease, is also a metabolic disorder, and can also include Insulin Resistance, but is not the same as EMS.


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What is Insulin Resistance in horses?

  • Insulin is the hormone in horses that takes glucose, which powers your horse’s cells, from the bloodstream into the cells to be used as fuel.


  • Glucose is a suger, which your horse makes from the carbohydrates in his diet. Your horse’s response to glucose in his body is insulin, and the horse with EMS produces too much insulin. When a horse is Insulin Resistant, or in a compromised state, your horse won’t respond properly to insulin, so your horse generally keeps producing more and more and more insulin to get the job done.



  • It’s widely thought that insulin can directly affect the laminae in your horse’s hooves, and increased levels of insulin create at the perfect storm for laminitis to set in. This is possibly due to a change in blood flow to the hoof caused by insulin. In a clinical setting, laminitis can be induced when horses are on IV drips of insulin. There is still a lot more to know about insulin and the hooves, but we do know that IR is a massive risk factor for laminitis. MASSIVE.


  • Insulin resistance is roughly equivalent to Type II diabetes in humans, and much like Type II diabetes, diet and exercise and lifestyle are key factors to change here!


very fat pony on short pasture grass

Cute, but basically a walking time bomb for laminitis and EMS.


The signs of EMS and Insulin Resistance in horses


  • Generally, horses and ponies from age eight and older are affected by EMS. Some research suggests that horses can be as young as five! FIVE.


  • Overweight horses are at risk! You might see a horse that is generally overweight, or you might see a horse that has fat deposits on certain parts of his body. You see these fat deposits on your horse’s neck and crest, above the eyes, behind the shoulder, the flank, and near the tail head.


  • A word of caution – weight alone is not a definitive diagnosis of EMS. Horses that are not obese or overweight can have EMS, and obesity is not a guarantee of this particular metabolic condition. Weight is just one factor to look at.


horse weight tape

Super easy to use. Takes mere moments and can alert you to extra pounds before your eyes ever notice any.


  • Horses that have a history of laminitis are at risk for EMS. Your horse doesn’t have to have a massive attack of laminitis, there are plenty of subclinical indications of laminitis that occur.


  • Your horse might get foot sore after grazing, a farrier visit, or hard work. This might be a sign that your horse has EMS, or you need to make some changes to how you manage your horse’s hooves.



  • You might also find changes to a horse’s fertility and an overall increase in appetite. Seriously? An increase in appetite? Don’t all horses act hungry all the time?



How is EMS diagnosed in horses?



  • Your horse’s vet can help determine if your horse has EMS, or is at risk of developing EMS. A body score evaluation can address your horse’s weight, as can regular weight checks with a weight tape. You can do these evaluations at regular intervals!


  • Your Veterinarian can also perform laboratory tests to determine if your horse has insulin resistance or is in a compromised state.


  • Routine blood tests like a complete blood count (CBC) and serum chemistry give your vet an overall picture of your horse’s health.


  • There are also tests specific for insulin and blood glucose, which can indicate IR. These are usually done after your horse has fasted. So be prepared for some major stink eye from your horse as he has to wait to eat. Hours. Probably best not to ride during that time.



blood drawn from jugular vein on horse

A tiny stabby stabby and it’s done.


  • There is also an oral sugar test that is suitable for horses that are not likely to have a laminitis episode because of a high sugar meal. Typically, a horse is given corn syrup, and at set intervals after the dose, blood glucose levels are measured. This test is thought to be more accurate when determining insulin resistance.


  • There is another test, The Combined Glucose Insulin Test (CGIT). This test starts with a baseline blood draw. Your horse is then given sugar via injection, followed by an injection of insulin. For the next several hours, blood samples are taken to measure glucose and insulin.


How do you manage EMS and help your horse?


  • The primary goal of managing EMS is to remove the risk of laminitis and alter your horse’s weight to a healthy level. This can be really tricky – and can take time. Management of the EMS horse requires creating a plan for each individual horse.


  • With regards to exercise, this ideally is part of your horse’s routine, unless there is active laminitis or another soundness issue to overcome. Ramping up an exercise plan requires daily attention and avoidance of the “weekend warrior” exercise plan. You also want to increase intensity and duration over time so your horse has a chance to acclimate over time.


  • If you are unable to ride, lungeing or hand walking are great ways to exercise a horse. And also you at the same time. Please don’t confuse turnout as exercise. Think about your horse meandering around a paddock the same way we meander around Target. Sure, you are getting your steps in, but compare that to actively marching around with purpose. Or even walking up hills or slopes. Make your horse’s day include active movement.



You must exercise your horse if he is able. No matter the weather.


There may be some supplements and medications that can help the horse with EMS.


  • Even though IR is similar to Type II diabetes in horse, the medications that help in humans don’t work in horses. Metformin is for diabetes in humans, and it’s barely metabolized by horses. Some horses may have some benefits with Metformin if given before meals. Your vet is definitely the expert here.


  • There are several supplements on the market that may help. As horse owners, it’s up to us and our vets to read the actual science, not the testimonials, about these supplements to determine if your horse could benefit.


  • Some horses are also put on thyroid medication which may or may not help. Some research suggests that thyroid medications can be discontinued after a certain period of time. Your vet and equine nutritionist are key team members here.


Your horse’s diet is also a key component to managing EMS.


  • You must reduce the amount of sugars and carbs in the diet. You should be feeding the lowest starch diet you can possibly find.


  • Hays should be low starch, and you can have your shipment tested. Less than 10% non-structural carbohydrates (NSC) is best.


  • For hay, you can also soak the meals to remove most of the sugars. Steaming hay won’t remove enough sugars to make a difference, you need to soak your horse’s hay.


  • It’s also a good idea to add in slow feeders and make sure the amount of hay you are feeding is appropriate. It’s rarely a good idea to drastically cut your horse’s hay intake. Go slowly, it takes time.


  • It’s also a fine time to remove all grains and fortified feeds that have high NSC values. There are plenty of feeds that are fine for horses with EMS, as long as the NSC values are below 10% and there are no extra calories.


  • Feeds can be calories and vitamins and minerals, called complete or fortified feeds, or just vitamins and minerals and far fewer calories known as ration balancers.


  • If you need to limit your horse’s diet to just hay, please make sure you have an appropriate vitamin and mineral supplement to provide those things that hay alone can’t supply. Your equine nutritionist is your best resource to find a balanced diet!


pink muzzle on a pony in a very green field

Muzzles are a must, dry lots might be even better. This is the Greenguard Equine Muzzle and it’s awesome.


You also need to limit your horse’s access to pasture.


  • For the horse with a history of laminitis, fresh pasture should be avoided at all costs.


  • For other horses, limited time on grass may be possible and the use of a grazing muzzle is encouraged. Most muzzles can reduce grass intake by 80% or so. This is to reduce the amount of high sugar grasses your horse eats.


  • It’s much safer to let your horse graze with a muzzle for a few hours than to let your horse scarf down as much as he can shovel in for an hour.


  • If you are unsure about your horse’s laminitis risk, skip all pasture. Dry lots are a super alternative and you can spread some slow feeders and horse toys around.


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Jolly Pets Horsemen's Pride Amazing Graze Toy

Keep your horse's brain happy!

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Great to use with buckets to discourage cribbing

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Equiessentials Slow Feed Hay Ball Large
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Grazing Muzzle by GG Equine

Basket-style grazing muzzle to help keep a horse at a healthy weight and help reduce the risks of colic and laminitis in some horses.

Use code 15PROEQUINE for savings sitewide on muzzles, halters, slow feeders, and more.

HayPlay Slow Feed Bag XL – GG Equine

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HayPlay Slow Feed Bag – GG Equine - 2 sizes available

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40 lb. Alfalfa Cubes
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