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Equine obesity: A talk about equine metabolic syndrome and laminitis

This is an accompanying article to a Cornell Equine Seminar presented Feb. 16, 2021 by Dr. Gillian Perkins, clinical professor in the section of large animal medicine.

Laminitis is a painful and potentially life-threatening condition, more likely to threaten horses that are overweight. Board-certified internist Dr. Gillian Perkins explains how to assess your horse’s body condition, what breeds are considered “easy-keepers,” and how to manage and treat equine metabolic syndrome and laminitis.

What follows here is an overview. Please watch Perkins’s entire presentation for more extensive information.

Is my horse fat?

One way to assess whether a horse is overconditioned or underconditioned is to use a body condition score. Many different models are available and look at where horses carry their fat, which is typically deposited in the withers, backbone, flanks, inner thighs, tail, head, and behind the shoulders and ribs.

The Henneke Body Condition Score, for example, ranges from one (poor) to nine (extremely fat). A horse with the lowest score is severely emaciated with bones and its pelvis visible. “Number four to five (moderate) is what we’re aiming for in our diets for our horses,” Perkins explains. “The back is flat, so they don't have a crease or ridge. There might be a little fat around the tail head and over the shoulders, and the neck kind of starts to blend into the shoulders and the body.”

Horses with scores of six (moderately fleshy) and above are considered overconditioned. They may have a visible ridge along their backs and fat over their ribs and tails and be rounder overall.

Perkins recommends using a weight tape to measure circumference of the horse monthly to track its weight loss or gain, and to get a sense of its overall body weight over time. “It’s very important to be consistent about how you’re positioning the tape around their withers and behind their elbows,” Perkins adds.

What's the big deal if my horse is overweight?

Overweight horses can get laminitis. “It is very severe and painful to horses and very hard to manage,” says Perkins. “They can have multiple episodes of laminitis, and it can be life threatening and the horse may need to be put down. So it’s really something we want to prevent.”

Equine Metabolic Syndrome

Some horses get heavy from being overfed for the amount of exercise they are doing. Others have Equine Metabolic Syndrome (EMS), a genetic disposition to gain weight, even with appropriate feedings. “These horses sometimes seem like easy keepers, they just sniff the oats and get heavy,” Perkins says.

When such horses have excessive exposure to carbohydrates – usually in the form of grain or grass – and aren’t exercised enough, they can develop insulin resistance and laminitis.

Breeds that are genetically predisposed for EMS include the pony (especially Welsh), Morgan, Norwegian fjord, Paso Fino, Peruvian Paso, Arabian, European Warmblood, American Saddlebred, domesticated mustang, Andalusian, Tennessee walking horse and quarter horse.

“You will likely have challenges with keeping the weight off of these horses and need to be very careful about offering them too much food,” Perkins says. They have “thrifty genes,” appropriate, for example, for mustangs that had to make do with the food they would find on the range – but less so in their new context of lush green grass, easy access to grain and less exercise. Donkeys are similarly prone to excessive weight gain.

Discussions suggest that historically, horses would go through cycles of gaining weight in the summer and losing weight in the winter when they have less access to forage and use up their fat stores – which may have been a cycle that prevents insulin resistance and reduces instances of laminitis.

Fat in the body

Horses with obesity may have abnormal fat deposits in certain parts of their bodies (regional adiposity) but be in good condition in other regions. A neck with fat along the upper curve feels thick and firm and is described as “cresty.” Obese horses may also have puffy tail heads, mammary glands that look swollen and eyes that appear bulgy – all of which is fat deposition.

Fat is not just a storage site for energy. Fat cells (adipocytes) also produce cytokines, inflammatory mediators and other substances that incite inflammation and predispose the body to other problems. An imbalance between certain types of hormones can result in insulin resistance.

Laminitis, or founder

Laminitis, or founder, is inflammation of the lamina, the connection between the hoof wall and the coffin bone inside the hoof capsule. With inflammation, the small, finger-like projections of the lamina die off and separate from the rest of the hoof. The bone may begin to shift and rotate within the hoof capsule, pulled by the force of a deep digital flexor tendon at the back of the horse’s leg, or it may sink down through the bottom of the foot.

Laminitis is generally worse in the front limbs but can affect all four limbs.

Causes of laminitis

Next to systemic inflammation from fat cells, research points toward insulin being toxic to the sensitive lamina tissue and is considered a major factor in laminitis development in horses with EMS.

Non-EMS causes of laminitis include:

  • Pituitary Pars Intermedia Dysfunction (PPID), an endocrine disorder, also known as Cushing’s disease
  • Support limb laminitis, e.g. when one limb is injured and the other bears more stress
  • Road founder from concussive forces
  • Severe illness, e.g. diarrhea, retained placenta, shipping fever
  • Toxins, e.g. black walnut, hoary alysum

What does it look like when my horse has laminitis?

Laminitis cases range from mild – which may go unnoticed – to severe, with horses unable to stand or walk. Horses with laminitis often walk as if on eggshells or refuse to move, rocking back on their hind end. Turning them typically is more painful.

In the early phases, their feet may be very hot. Perkins also palpates the blood vessel running down the back of the leg known as the digital pulse, this will be bounding.

Evidence of previous episodes of laminitis can be seen in the widening of hoof rings at the heel.

Veterinary examination

“If you feel your horse has any of these problems, you should call your veterinarian,” says Perkins. The veterinarian will determine the horse’s body condition score and watch the horse move. A brief lameness exam including turning the horse often reveals enough information. A hoof tester helps to confirm the diagnosis, as does a palmar digital nerve block that can be required to obtain radiographs. Blood tests can be done to test for EMS.

Blood tests

The focus of a blood test is on insulin, a hormone that regulates glucose by letting it into cells. Horses with EMS tend to have insulin resistance and show high levels of resting insulin concentrations (hyperinsulinemia). A normal test result could be a false negative, so Perkins still recommends dietary changes to horses that are obese to reduce the risk of laminitis. With a normal result, a secondary test called the sugar test can be done to confirm a diagnosis of EMS.

Oral sugar test

For an oral sugar test, the horse needs to fast overnight after having only one flake of hay before midnight. The vet comes out in the morning to give the horse Karo-light syrup and collect blood at 60 and 90 minutes. Horses with EMS will show a large surge in their insulin at the time of testing.

Other tests

EMS and PPID can occur at the same time, so it makes sense to test a middle-age or older horse with laminitis and insulin resistance for both disorders. PPID can be addressed with pergolide, a daily treatment.

Additional tests look at other hormones, such as leptin – usually high in fat horses – or triglycerides, though these are less commonly used. A test for adiponectin will probably become available in the future.


The veterinarian can take radiographs of the hooves to see how the bone is sitting within the hoof capsule and whether any gaps show in the laminar tissue. Initial images serve as a baseline to compare future progress against. They can also be used to help guide the farrier with trimming.

Treatment of EMS: Diet

A large part of treatment consists of dietary management, mainly by limiting carbohydrates and fats. If a horse is not getting any exercise, it does not need grain and should be fed only hay. The appropriate amount of hay is equal to about 1.5 to 2 percent of body weight per day. For example, a 1,200-pound horse gets 18 to 24 pounds of hay, less if it is supposed to lose weight. “Weighing the hay is extremely important to know how much you’re feeding them,” Perkins emphasizes.

Hay should not be high quality. “It’s kind of counterintuitive,” Perkins says. She recommends grass hay with non-structural carbohydrates (NSC) of less than 10 percent. You can send a hay sample to a lab to have this value measured, along with water-soluble carbs (WSC) and starch. Not all labs report NSCs. One lab that Perkins recommends is Equi-Analytical in Ithaca.

Hay should be provided multiple times a day. An option to slow the horse down is to use a nibble net. On a hay-only diet, Perkins says that providing a mineral supplement is a must. In the northeast, for example, horses on hay only diets will not get enough selenium.

If you don’t know the hay quality, soaking the hay 30 minutes prior to feeding is a good way to reduce the WSCs up to 50 percent. You can also look for low-NSC pelleted hay or Timothy Balance cubes.

As for treats, “you should only give them in moderation,” Perkins adds. Feed just a chunk of carrot instead of the whole vegetable.

Because grass has a variable sugar content, you should avoid turning horses with EMS out to pasture. “That’s sad to us, because we feel horses are happy out on grass, but we’d be killing them with kindness,” she says. “We don’t want them to develop laminitis.” Instead, horses can spend time on a dirt lot. If they have companions without EMS, they can be near each other on appropriate but separate paddocks.

If a horse previously diagnosed with EMS has a good body condition score and blood sugar tests are normal, you may decide to put it out to graze for short periods (under 30 minutes), depending on how much it eats during that time. Grazing muzzles – properly fitted and managed – can reduce the horse’s grass consumption. If a horse with well managed EMS is exercised, it may also eat small amounts of grain.

Overall, horses should lose weight slowly, just like people.


Exercise – such as lounging, trail riding or moving around an arena for just 30 minutes three times a week – helps with insulin sensitivity. Getting this amount can be difficult if the horse is sore from laminitis. “Then it becomes even more critical to deal with the diet,” Perkins says.


If dietary changes haven’t made a difference after 30 days, your veterinarian may suggest thyroid supplementation. Sometimes, however, a horse will regain weight when going off the medication, so Perkins emphasizes working on diet and exercise program.  She reserves medications such as metformin for uncontrolled insulin resistance and severe laminitis cases.

Laminitis treatment

To control laminitis pain in an acute episode, Perkins prescribes non-steroidal anti-inflammatories such as phenylbutazone. Rest is very important, as is a stall with deep bedding or sand. Soft rides or lily pads support the hoof. “Of course, we always want to address the underlying cause, so if it's EMS we want to work on their diet to control insulin concentrations,” Perkins says.

The hoof also needs consistent care and evaluation from the farrier, who will trim the excess toe and allow the heel to grow and establish normal angles in the foot. Frog support shoes help with pressure underneath the frog of the foot. “The farrier can make a huge difference in how comfortable the horse is,” says Perkins.

Obese horses and EMS

Having a horse genetically predisposed to EMS means committing to lifetime management and treatment through diet and hoof care. Laminitis is a painful and life-threatening condition. “You have to be very vigilant and partner with your veterinarian and farrier to provide the best care for your horse,” Perkins emphasizes. That includes avoiding grass and greens, which are like candy for horses. “If I had one slogan for the talk, it would be ‘hay is for horses.’”

Watch Perkins’s full talk online and see the entire Cornell Equine Seminar Series videos here.