EQUINE METABOLIC SYNDROME

What is Equine Metabolic Syndrome (EMS)?

EMS is a term used to describe horses that have a cluster of physical signs and physiologic changes including;

• Obesity
• Regional Fat Deposition
• Insulin Resistance (IR)
• High Susceptibility to Laminitis
• “Easy Keepers”

Other names used in the past to describe these signs were Insulin Resistance Syndrome, Peripheral Cushing’s Syndrome, Syndrome X, Omental Cushing’s Syndrome, Central Obesity, Hypothyroidism and Pre-laminitic Syndrome. Equine Metabolic Syndrome replaces these previous terms.

As of now, we do not know the eitiology of EMS but there may be a genetic predisposition to it. It is seen more commonly in Arabians, Morgans, Paso Finos, Mustangs, American Saddlebreds, Ponies, Tennessee Walking Horses and Quarter Horses. Affected animals may possess a “thrifty gene” that enabled their ancestors to survive in very harsh environments.

EMS horses respond abnormally to high carbohydrate meals with an exaggerated increase in insulin and a very slow return to baseline. EMS horses have both a resistance to the effects of insulin and an inability to metabolize carbohydrates normally. All EMS horses are Insulin Resistant but not all Insulin Resistant horses have EMS.

Why is it Important to Diagnose Equine Metabolic Syndrome in Horses?

Humans with Metabolic Syndrome have an increased risk of Coronary Artery disease which can lead to death. Horses have an increased risk of Laminitis which can lead to death. If we identify and treat EMS, we can decrease laminitis.

How Do We Diagnose Equine Metabolic Syndrome?

It is important to realize that horses can be obese due to high caloric intake and not EMS.

There is no one test to definitively diagnose EMS. The two most reliable tests are reserved for research settings and not practical in practice settings. We use a combination of physical signs like obesity (BCS 7,8,9) and fat distribution (neck, tail head) along with demonstration of Insulin Resistance with lab tests. If a horse has laminitis when we examine it, EMS is more likely.

All of the laboratory tests for IR have a lot of variability – none are perfect. There are 5 recognized tests for IR. The least expensive, easiest and least reliable is testing baseline insulin and glucose levels after a controlled overnight fast. The most expensive and most reliable is the combined glucose insulin test that involves giving insulin and glucose to the horse and running several blood tests over a couple of hours to create a graph which can then be interpreted. This test is the one recommended by the ACVIM. The other tests are the oral glucose tolerance test, the intravenous glucose tolerance test and the insulin tolerance test. These three fall, in price and reliability, between the other two tests.

What Horses Should be Tested?

• Any horse with the physical signs of EMS that is getting a normal diet
• Any horse with laminitis that is unexplained

How can we Treat Equine Metabolic Syndrome?

There are three very important components to treatment; exercise, diet and medication.

Exercise treatment

Muscle is the largest organ in the body with insulin-mediated uptake of glucose so it is extremely important in whole body regulation of insulin and glucose dynamics. We can not treat this disease without increasing exercise. There are many ways to accomplish this:

• At least 30 minutes of daily trotting and cantering each day
• Enlarge pens and paddocks
• Daily turnout
• Toys like balls or cones
• Spread food and water around the pen
• Put the horse by itself – studies with GPS on horses shows that they move more alone than with others
• Treadmills
• If the horse is painful and laminitic, walking or water treadmills are ideas

Diet modifications

EMS horses need a low soluble carbohydrate, low glycemic index, low fat diet. This is best accomplished with a diet of grass hay at 1-1.5% body weight per day and a calorie free vitamin and mineral supplement.

If you buy a lot of hay at a time, it is worth getting a hay sample analysis done (www.equi-analytical.com). The goal is to have less than 15% non-fiber carbohydrate and less than 10% non-structural carbohydrate on a dry matter basis.

Soaking (submerging) hay underwater for 30-60 minutes before feeding will leach out some of the soluble carbohydrates which is very helpful for EMS horses.

There are several supplements that have been shown in humans to increase cell responsiveness to insulin. Many of these have been suggested for horses including herbal preparations, chromium, cinnamon, magnesium and vitamin E. Unfortunately, there are good studies to show that they do not help IR horses. The following food items have high glycemic indexes and should not be fed to EMS or IR horses; molasses, carrots, apples, grain, corn, oats, barley. Pasture is also not good for these horses.

One way to help these horses with such a limited diet is to use a slow-feed system for feeding. There are slow-feed hay bags as well as feeders like the porta-grazer that decrease the amount of feed a horse gets in each bite which really seems to help the horse mentally and physically.

Medications

Thyroid hormone (levothyroxine sodium) has been shown to increase metabolic rate , increase insulin sensitivity, increase fat mobilization and may even increase blood flow to the feet. EMS horses are generally put on the medication for 3-4 months and then may need to stay on it longer or may be able to get off of it. This only works with diet restriction as well. If you don’t modify the diet, they will just eat more.

Various medications that improve insulin sensitivity in humans have been attempted on horses. At this time, none has provided consistent results.

Christine Staten, DVM, Adobe Veterinary Center, Tucson, AZ

This article was written with information current as of October 2011. There is a lot of EMS research at this time so information is always changing. Because EMS is not a simple disease to diagnose or treat and because all horses need management tailored to their specific situation, please consult with your own veterinarian for advice about you particular horse or situation.