Equine Metabolic Syndrome

Do you have a horse or pony that lives off next to no feed and you can't seem to get him to lose weight despite an intense exercise program? Does he have repeated episodes of laminits for no obvious reason and have you recently noticed that he is developing a cresty neck, odd fatty lumps over his withers, tail head or above the eyes? If the answer is YES to any of these findings then read on. It is very possible that your horse is suffering from the recently described condition of Equine Metabolic Syndrome.

The term 'Equine Metabolic Syndrome' is a term that has been adopted in recent years to describe a collection of clinical signs/diseases that contribute to the development of slow-onset laminitis. The precise definition of this syndrome is ever-changing but is is currently defined by the presence of 3 tightly interlinked conditions:-

1. Insulin resistance
2. Obesity and/or abnormal fat deposits
3. Prior or current laminitis

Knowledge of Equine Metabolic Syndrome is useful since it allows owners and vets to recognise horses and ponies that are high risk candidates for developing laminitis. In turn, effective management of this condition appears to help in the prevention of laminitis. Typically, horses or ponies that are affected with Equine Metabolic Syndrome are between 8 and 18 years of age. There is no one equine breed that is at risk but classically the horse or pony that is described by the owner as a 'good doer' is a perfect candidate. Both male and female horses and ponies are equally likely to suffer from this condition. Physical characteristics of Equine Metabolic Syndrome include generalised obesity and/or regional fat deposits such as a cresty neck or swollen sheath. Laminitis, abnormal reproductive cycling in mares or colic secondary to pedunculated lipomas are all possible reasons your veterinarian may be called.

Insulin resistance
Insulin is a hormone secreted by the pancreas that stimulates the uptake of glucose (sugar) into tissues where it can be stored as a future source of energy. Insulin resistance can be defined as a failure of tissues to respond appropriately to insulin.

Insulin resistance

• High blood glucose
• More insulin released by the pancreas to try and drive the glucose into the tissues
• High blood insulin concentration
• Impaired glucose delivery & altered blood flow to the hoof tissues
• Laminitis

If the insulin resistance is left untreated it is now recognised that horses can suffer from Type 2 diabetes similar to humans where they develop high blood glucose concentrations which, in turn, can lead to clinical problems, eg excessive urination.

Testing for Equine Metabolic Syndrome

1. Clinical presentation
   • The presence of an overweight, laminitic horse or pony will raise your veterinarian's suspicion that Equine Metabolic Syndrome may be an underlying cause of your horse's ill health.
2. Measuring blood insulin concentration
   • Blood samples must be collected from horses that have been held off pasture for at least 12 hours and fed only hay overnight. Grazing on pasture or feeding concentrates will elevate the blood concentration of insulin due to the high sugar content of such feeds, thereby making it difficult to accurately interpret the results.

Management of Equine Metabolic Syndrome

1. Reducing obesity
   • Obese horses that are 'easy keepers' can be placed on a simple diet of hay and a vitamin/mineral supplement. Concentrates are not necessary for these obese horses and weight loss should be promoted by restricting the horse's caloric intake until the ideal weight and body condition have been achieved.
   • Obese horses should be fed enough hay to meet their resting energy needs, yet promote weight loss. This can be achieved initially by feeding hay in an amount equivalent to 1.5% of their current body weight (ie 7.5kg hay for a 500kg horse) and then lowering the quantity of 1.5% of their ideal body weight until weight loss has been achieved.
   • Horses that are lame because of laminitis should not be exercised until hoof structures have stabilized but all other horses should be exercised as often as possible.
2. Managing insulin resistance
   • Weight loss and exercise both improve insulin sensitivity but it is also important to avoid feeds that exacerbate insulin resistance. The horse with Equine Metabolic Syndrome is similar to a person with diabetes so sugar should be avoided. Unfortunately, it is somewhat difficult to control sugar intake in horses that are on pasture due to the variable content of sugars in grass so access to pasture must be restricted or eliminated when managing horses or pastures with Equine Metabolic Syndrome. Sometimes this is only necessary for weeks or months until the ideal body condition has been achieved.
   • Insulin sensitizing drugs such as Metformin are available and have been found to be a means of effectively reducing blood insulin concentrations thereby reducing the clinical signs of laminitis. If a blood test shows that your horse has a high insulin concentration and is thereby suffering from Equine Metabolic Syndrome, Metformin treatment is simple to give to your horse and relatively cheap but is a lifelong therapy.
3. Treatment of laminitis
   • Rest and pain management are the key to treating laminitis but in the horse affected with Equine Metabolic Syndrome weight loss and improving insulin resistance will both result in a rise in the threshold for the associated laminitis. This will speed up your horse's recovery and reduce the risk of future laminitic episodes. Regular trimming of your horse's feet will enable your farrier to record signs of laminitis in your horse's hoof before pain is evident. In severe episodes of laminitis radiographs of the hooves may be indicated to determine if the pedal bone has rotated or sunk within the hoof capsule.

In conclusion, Equine Metabolic Syndrome is a condition that is becoming increasingly well recognised. After many years of struggling to understand why some horses and ponies continually suffer from laminitis, despite what may seem to be the best of care we, as veterinarians, can offer some explanation. A simple blood test to measure blood insulin concentrations followed by diet changes, exercise and possibly medication may help relieve your horse of the crippling discomfort associated with laminitis and allow your horse to lead an active and comfortabl