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Illinois Livestock Trail
Dealing with “Equine Metabolic Syndrome”
by Kevin H. Kline, PhD Professor of Animal Sciences University of Illinois

Equine Metabolic Syndrome is basically a "prosperity disease" of horses that are genetically thrifty. In other words, some types of equines including certain pony breeds, Morgans, Pasos (Paso Fino, Peruvian Paso), domesticated Spanish Mustangs and occasionally warm blood breeds of horses are genetically well-adapted to surviving under harsh conditions, including relatively low feed intakes. When too much "prosperity" or plenty of rich feed is available, these "EMS" horses may suffer from obesity, uneven fat deposition along the crest of the neck and tail head, insulin resistance and laminitis. The peculiar fat deposition patterns in some EMS horses may also include fat bulges above the eyes, behind the shoulders, and in the sheath of male horses, even when these horses are relatively thin overall, and have not received a great deal of excess dietary energy.

In past years, many of these horses would have been labeled as "hypothyroid horses", because some do in fact have low thyroid hormone concentrations. However, more recent research suggests that hypothyroidism may be more of a consequence of the condition, rather than a cause; and that not all EMS horses have low thyroxin concentrations. Equine Metabolic Syndrome is most likely to be diagnosed in horses between 8 and 18 years of age. When younger EMS horses are in heavy training for various competitive or intense recreational events, and are consuming just enough energy to cover the demands for growth and exercise, the condition may not be readily apparent. As an EMS horse becomes less active, but may still be receiving similar amounts of hay, grain and pasture, symptoms worsen.

The most debilitating part of Equine Metabolic Syndrome is the associated laminitis or "founder", which can permanently cripple a horse if enough sensitive laminae in the hoof are damaged. It is thought that insulin resistance is the component of EMS that predisposes horses to laminitis. Insulin resistance basically means that normal concentrations of insulin that should induce expected changes in target tissues (ie: facilitating uptake of glucose from the blood by muscle, liver, fat and other tissues) fail to cause those expected changes. The horse's pancreas then compensates by secreting higher and higher levels of insulin to cause the required responses in body tissues. This excess insulin causes numerous negative health consequences that equine researchers are actively studying, in hopes of finding more effective treatments for horses that suffer from this condition.

The currently recommended management-related treatments for EMS horses that are prone to obesity and laminitis include reducing the overall caloric intake, decreasing the starch and sugar content of the diet (no grain!!), increasing exercise, and limiting access to pasture. Some varieties of pasture grass contain more sugar and starch than others, so contact your nearest

Extension Horse Specialist for advice on pasture management for EMS horses. Some severely affected horses may need to be kept off pasture altogether to avoid recurring problems with laminitis.

Some medical therapies are available for treatment of EMS horses as well. These include treatment with Levothyroxine sodium, which recent research has found to accelerate weight loss and increase insulin sensitivity. However, medical intervention is expensive, and should be considered to be short-term assistance to speed weight loss and improve insulin sensitivity while management practices are being implemented in order to reduce the likelihood of laminitis. There is no miracle cure available for horses with Equine Metabolic Syndrome, but proper management, especially avoiding grain and increasing riding time in affected horses, can greatly improve the quality of life for EMS horses.

Fresh from the AAEP Annual Convention, here's an update on what we know about these two disorders and how to manage them:

Equine metabolic syndrome typically affects horses aged 8 to 18-years-old. Pony breeds, domesticated Spanish Mustangs, Peruvian Pasos, Paso Finos, and some Warmblood breeds appear especially prone. A preliminary diagnosis is based on obesity, insulin resistance and insidious onset of laminitis. EMS horses typically have fat deposits in the crest of the neck, over the tail head, above the eyes, behind the shoulders, and in the sheath of male horses. Diagnosis is confirmed by measuring insulin and glucose levels in the blood. Unfortunately, there are no medications to treat EMS. At this time, experts recommend a low sugar/starch diet, exercise, and antioxidants such as Vitamin E to help manage the oxidative stress that comes with the syndrome.

Signs of equine Cushing's syndrome typically first appear in horses aged 18 to 23-years-old and include: hirsutism (long curly hair), weight loss and muscle atrophy, depression and poor performance, normal to increased appetite, laminitis, and fat deposits as described above. The best tests for Cushing's are the dexamethasone suppression test and the ACTH stimulation test. And while the disease cannot be cured, pergolide seems to help manage the disease better than cyproheptadine. Because some horses with Cushing's develop insulin resistance, they should also be fed a low sugar/starch diet, although some might need additional calories from fat. Antioxidants might be useful in this syndrome as well.

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