A COMMON PROBLEM
Although it can’t quite be considered normal, pituitary pars intermedia dysfunction (PPID, colloquially known as Cushing’s syndrome) is very common in older horses. An estimated 70 percent of horses over age 25 have some degree of PPID.
In horses with PPID, a malfunction of the pituitary gland inside the brain causes the secretion of excessive levels of the hormone adrenocorticotropin (ACTH). This then triggers the adrenal gland to increase the production of cortisol, and the resulting imbalances lead to the hallmarks of PPID: a long, shaggy haircoat that is slow to shed, lethargy, loss of muscle mass, laminitis and susceptibility to infection. Identifying and controlling PPID is an important part of maintaining an older horse’s health and well-being. That means it's a good idea to test any older, slightly shaggy horse for PPID. The two most commonly performed test are the ACTH test which is a one-time blood test that measures levels of ACTH, and the thyrotropin-releasing hormone (TRH) stimulation test which compares the level of ACTH before and after administration of TRH. The test or combination of tests that will be best for your horse depends on several factors including his overall health, the time of year and your geographic area. Your veterinarian will know which test is most suitable for your situation.
If your horse receives a PPID diagnosis, you can take immediate steps to limit the condition’s effects. Pergolide mesylate (product name Prascend) is the only medication approved by the Food and Drug Administration for treating the disorder.
In efficacy studies, 76 percent of horses showed some improvement in their clinical signs within 30 days of starting pergolide treatment. Within six months, 89 percent of horses had improved haircoats and 46 percent showed improvement in muscle tone. One important point: Cheaper versions of pergolide offered through some compounding pharmacies are illegal, and studies have shown them to be unstable and probably ineffective because of extremely specific storage needs of compounded formulations.
In addition to giving your horse medication for PPID, you can keep him more comfortable by clipping a slow-to-shed coat when spring arrives. Also, because PPID is linked to a higher incidence of laminitis, consider switching to a feed that is low in sugars and nonstructural carbohydrates to avoid triggering an episode— and be extremely careful about putting a horse with PPID on lush pasture in the spring and fall. Routine hoof care is especially important for horses with the condition, as are regular vaccinations and parasite control.
A horse with PPID will need to remain on medication for the rest of his life. The good news is that pergolide tends to work well and the condition can be successfully managed for many years.