Horses today live longer. Through better parasite control, dental care, and preventive medicine practices it is common to see horses in their 20’s and 30’s. Living longer brings about health issues that are more common today than in the past.
Cushing’s disease is a name that has been used to cover several different diseases. True Cushing’s or Central Cushing’s involves dysfunction of the pituitary gland. This in turn leads to an increase in fluid cortisol levels. An increase in the compound cortisol leads to insulin resistance and abnormal glucose metabolism. These horses will have increased insulin levels in their blood.
Signs associated with Central Cushing’s include excessive coats that fail to shed, laminitis, and increased drinking and urination. Testing for Central Cushing’s is done with the dexamethasone suppression test. If Central Cushing’s is diagnosed it is treatable with a daily medication called pergolide.
A similar disease had been noted which commonly occurs in obese horses. This disease has been called peripheral Cushing’s or more recently Equine Metabolic Disease.
Horses affected with Equine Metabolic Disease have some signs similar with Central Cushing’s, such as abnormal deposits of fat, increased insulin levels and laminitis. The two diseases can be distinguished with dexamethasome suppression test.
Equine Metabolic Disease is thought to be associated with fat horses because fat cells can produce cortisol along with other hormones that cause insulin resistance. Not all fat horses are insulin resistant. This is thought to occur because some horses have fat cells that produce high levels of cortisol while some do not. This high cortisol level interferes with insulin activity. Insulin helps cells of the body utilize glucose. When the body cannot utilize the glucose in the bloodstream, the glucose increases, which triggers insulin release at excessive levels leading to elevated levels of insulin in a blood sample.
Why does Cushing Disease and Equine Metabolic disease cause laminitis?
Increased insulin and abnormal glucose metabolism causes changes in the vascular and cellular level of the foot which leads to laminitis, abnormal hoof wall growth, and foot pain.
Treatment of EMD should focus on reduction of fat cells. Starchy feeds should not be fed. Unlimited access to good pasture may need to be halted. Our patients routinely consult with a veterinary nutritionist when designing a diet plan.
Exercise is very important to rid the body of fat cells. If the horse’s foot condition will allow it, exercise is a great way to shed pounds.
Miscellaneous drugs and supplements have been used to fight Equine Metabolic Disease. Pergolide is not effective in treating EMD. The bottom line is that EMD is difficult to treat. The disease is much easier to prevent by not allowing our horses to become obese.
The disease process can be monitored by taking follow-up blood insulin levels. This gives us an ongoing way to monitor the animal’s response to therapy.