PPID (a/k/a Cushing's Disease) is an endocrine (hormonal) disorder in horses resulting from enlargement of the pars intermedia (the central part of the pituitary gland), which causes the overproduction of the steroid cortisol and a cascade of other metabolic consequences.

PPID is a very common condition in older horses of all breeds. It has historically been confused with Equine Metabolic Syndrome (EMS) which is a separate problem.

PPID should always be suspected in older horses that suddenly appear lame, have non-healing or slow healing wounds, or begin to lose weight for no obvious reason. A long, shaggy, (sometimes curly) hair coat that does not shed in the summer is a classic signs of PPID, however many horses with the disease do not exhibit this sign. Patchy shedding (with hair retained on the legs or underbelly later into the season) is also common. The retention of so called "goat hairs"- long guard hairs late into the summer is another common finding.

Laminitis is the most serious consequence of this disease. However, horses with PPID have decreased immunity, subjecting them to other diseases and illnesses. Even eye infections and ulceration are thought to be more common and serious in horses afflicted with this condition.

Diagnosis is easy in the advanced "classic" case with long, curly coat and often chronic laminitis. In earlier, less obvious cases, diagnosis requires the use of blood ACTH testing.

There is no cure for PPID, but medications that suppress overproduction of certain hormones and stimulate production of dopamine can lessen symptoms.