Equine Cushings Disease

Equine Cushing’s disease, more accurately called pituitary pars intermedia dysfunction (PPID), is a disease of the endocrine system. The endocrine system, through a series of glands, controls bodily functions by secreting hormones into the bloodstream. PPID affects the pituitary gland which is the most important endocrine gland. Many of the hormones from the pituitary affect the functioning of other endocrine glands. In equines, PPID causes the pars intermedia portion of the pituitary gland to grow larger. In turn, the gland produces an excess of adrenocorticotropic hormone (ACTH). ACTH is responsible for directing the adrenal gland to secrete cortisol. Horse’s with PPID, therefore, have an excess of cortisol in their bloodstream.

PPID occurs most often in horses older than fifteen years, but younger horses can be affected too. Ponies and Morgans are most commonly affected. The most telling indication is a long, thick hair coat that is slow to shed. This is known as hirsuitism. Other symptoms are frequent drinking, excess urination, profuse sweating, loss of muscle. Horses with PPID have a suppressed immune system. For this reason, horses with chronic infections should be tested for PPID. Treating PPID will subsequently aid in the bodies ability to fight infection. Horses with PPID are prone to laminitis and may be insulin resistant. PPID is progressive, so this disease will get worse over time.

There are two blood tests for PPID, and neither is entirely accurate. Veterinarians often test the blood for ACTH. Elevated levels of ACTH can indicate PPID, but a horse can have varying levels in the blood throughout the day. A second, more involved, but slightly more accurate test is the dexamethasone suppression test. Blood is drawn from the horse then the horse receives an injection of dexamethasone. Nineteen hours later more blood is drawn. In a healthy horse, dexamethasone will suppress the levels of cortisol in the blood. A horse with PPID will have cortisol levels that remain unchanged.

Diseases of the endocrine system can sometimes be difficult to diagnose. Work with a veterinarian to find the cause of the problem even if it takes several months. PPID can not be cured. Treatment with the drug pergolide and diligent, consistent care can improve the quality of life for the horse. Since these horses are at risk for laminitis, they should be fed accordingly. A low sugar, low starch diet consisting mainly of grass hay is best. When extra calories are needed rice bran or corn oil can be added to their ration. Shaving their coats to help them stay cool in warm weather is also beneficial.

References:

Tan, Jean-Yin Making Sense of the Cushings-EMS-Hypothyroidism Puzzle The Horse

Cushings Disease – AAEP Article


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