Equine Cushing's Disease

Equine Cushing’s Disease, is otherwise known as pituitary pars intermedia dysfunction (PPID). It involves the pituitary gland which sits at the base of the brain. The pituitary gland controls hormone production and with this disease the mechanism is disrupted causing excessive hormone production. These hormones effect the whole body.

Clinical signs include:

• Increased coat length (hypertrichosis)

• Delayed shedding of the winter coat

• Laminitis

• Hyperinsulinemia

• Larger fat pads above the eyes

• Lethargy

• Increased sweating

• Weight loss

• Excessive drinking and urinating

• Increased susceptibility to infections such as skin infections

The average age of diagnosis is 19 years, but it can affect horses as young as 10 years. Ponies are more likely to be affected than horses, and mares and gelding are equally likely to be affected. In recent European studies have shown that 21-22% of aged horses and ponies had PPID base on endocrine testing.

Diagnosis is based on history, clinical signs, and specific hormone tests. The testing is complicated by seasonal variation, the slow progressive nature of the disease, and false negatives. The secretion of ACTH is affected by day length, with increased secretion associated with decreasing photoperiods during the late summer and autumn.

There is no cure for PPID, but we do have treatment options. Pergolide mesylate is available as a liquid and tablet. The tablet is a more stable, has extended shelf life, and is the most common form of treatment. There is now a new medication, Cabergoline which is a long acting injection, to be used where pergolide is ineffective or where weekly or fortnightly injections are more practical than daily administration.