Cushings syndrome in horses is caused by a disorder of the pituitary gland that changes the hormone levels in the body and the way the horse responds to its natural steroids. It can cause muscle wasting and fat redistribution resulting in a horse that has a poor top line and a big belly. It can cause horses to have difficulty shedding out in the spring and may interfere with normal insulin and glucose regulation. It is often diagnosed by a dexamethasone suppression test where blood is drawn, dexamethasone is given, and blood is drawn again a number of hours later to determine the response to the dexamethasone. Insulin levels are an easy way to monitor control efforts. Horses should be put on a low starch diet, and pergolide or cyproheptadine may be necessary to control the disease. Vitex or chaste berry extract is an herbal way to control the disease that works for some horses.