Most horse owners I know have at least one “easy keeper”. These horses seem to require very little in terms of nutrition to maintain their body condition. Often the battle is in keeping them from becoming obese and horse owners go to great lengths, even what seems like near starvation to prevent these “easy keepers” from getting fat. As with all species, unchecked obesity comes with great health risks and for horses, Equine Metabolic Syndrome (EMS) is a condition not too uncommon for the overweight horse.
EMS is a complicated endocrine disorder of the horse and much remains to be discovered as to the intricacies of this disease and its most effective diagnosis and treatment. However, the primary abnormalities associated with EMS include abnormal fat deposition within the body, insulin resistance and Cushing’s-like (excess of the hormone cortisol) symptoms. Horses with EMS often have excessive fat deposition over the crest of the neck, the back and around the tailhead. Excessive abdominal fat is also a component of the syndrome and it is understood that this fat tissue is responsible for the production of hormone-like compounds within the body that create a resistance to the normal action of insulin within the body to regulate blood sugar. This fat tissue can also contribute to a relative increase in circulating cortisol levels in the blood. Chronic laminitis might be the most significant of the clinical signs associated with this disease. Horses may have recurrent bouts of mild founder resulting in abnormal hoof growth, lameness and rotation of the coffin bone within the foot.
Definitive diagnosis of EMS is challenging. There is not a clear and simple approach. If a horse presents with clinical signs consistent with the disease one of the first steps is to rule out other endocrine disorders such as Cushing’s disease or hypothyroidism. From there, glucose tolerance testing is recommended in which glucose and insulin levels are recorded. For the most accurate results, most veterinarians recommend testing be performed at a referral center due to the complexity of the diagnostic procedure. If insulin resistance within the body is demonstrated and not explainable by any other mechanism, then the horse is considered to have EMS.
Most horses affected with EMS are between the ages of 8 and 18. Ponies are more likely to be affected than most horses. The syndrome is thought to be related to the genetics of the animal as some breeds of horses such as Morgans and Peruvian Pasos are more frequently diagnosed. It is also thought that excessive feeding of concentrates to horses when they are young predisposes to the formation of fat within the body that is hormonally active, leading to EMS later in life. Therefore, prevention is aimed at avoiding excessive grain consumption and maintenance of a proper body condition score throughout life.
Encouraging weight loss in obese horses with dietary management and exercise and treating routinely during episodes of laminitis are the most reasonable treatment options at this time.
Darren Loula, DVM, is a large animal veterinarian at Fair Grove Vet Service in Fair Grove, Mo.


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