Equine Metabolic Syndrome
Laminitis is a common and painful condition that has been affecting all types of equine for centuries. Equine Metabolic Syndrome (EMS) is an endocrine disorder of ponies and horses, and is responsible for many cases of laminitis. Cushings disease is another hormonal dysfunction that also predisposes to laminitis, but usually occurs later in life. Approximately 9 out of 10 cases of laminitis have an underlying hormonal disorder, and most occur in native-breed ponies that are good-doers, and frequently have fat deposits in their crest, shoulders, tail-head and peritoneal cavity.
Several factors are associated with EMS, including adiposity (the laying down of fat, as described above), and insulin resistance (allowing too much insulin to be present in the blood stream). There may also be other factors, as yet unidentified. Eating grass containing simple sugars, fructans and starches stimulates the production of insulin, and is the final trigger leading to laminitis. These simple sugars accumulate in the grass during the Spring and Summer, and laminitis-prone individuals tend to produce far higher levels of insulin than normal horses and ponies do.
Diagnosis of EMS: the ‘glucose challenge test’ measures the amount of insulin produced in response to the feeding of glucose (a simple sugar). Laminitis-prone equines have normal (i.e. low) fasting insulin blood levels, but have exaggerated insulin responses when fed simple sugars. Overnight starvation (fasting) is followed by feeding chopped chaff mixed with 0.5g/kg bodyweight glucose or dextrose powder. Blood insulin and glucose are measured two hours later.
Management of EMS: this simply involves bodyweight control. The natural environment for native ponies is where grass grows poorly, and this is why the body has developed a system to cope with it. Most of Monmouthshire has improved pastureland and our ponies can only cope with it if the energy is burnt off by exercising regularly. If ponies are not worked their grazing has to be restricted. Those with EMS must come off the grass and be fed a limited amount of soaked hay and chaff, with supplementary vitamins and minerals. As a guide, the total daily dry weight fed should be 1.25 to 1.5% of bodyweight (i.e. less than 4kg for a 300kg pony) until an acceptable bodyweight is attained; fine mesh or triple netted hay nets will prolong feeding times. It may be necessary to use grazing muzzles during high risk times of the year. Daily oral medication with metformin has been found to be useful, and works by decreasing blood glucose and insulin concentrations. This should not be prescribed without blood confirmation of an EMS diagnosis. Regular farriery should also be incorporated into the treatment schedule, and x-rays of the feet may be necessary to check for rotation of the pedal bone within the hoof capsule.