It is caused by a small benign tumor in the pituitary gland. Since the pituitary runs the entire endocrine system, a number of conditions are associated with the disease. Cushing's disease is also referred to as hyperadrenocorticism. A horse with Cushing’s usually develops the condition in the mid to late years of life (average age, 20 years), although it is sometimes diagnosed in horses as young as seven.

The most common symptoms of Cushing’s syndrome are:

	Sudden-onset polydipsia (excessive drinking). An affected horse may drink as much as 20 gallons of water a day (as opposed to an average 5–8 gallons). This condition is usually accompanied by frequent urination.
	Abnormal hair growth and shedding. Some may develop a growth of heavy, coarse, often curly hair, which does not shed in the summer.
	Development of a swayback stance and a pot belly.
	Fat deposition above the eyes.
	Lethargic, dull eyes and drab coat.
	Increased appetite (little to no weight gain).
	Chronic laminitis.
	Loss of muscle over the back.
	Compromised immune system. This gives rise to a host of conditions/diseases which are often passed off as old age. Such as respiratory diseases, skin infections, abscesses of the foot, mouth ulcers, and periodontal disease.

Blood and urine tests are usually used to diagnose Cushing’s disease. Repeat testing may be necessary, as initial tests don’t always produce conclusive results. Some cases of Cushing’s syndrome are so obvious (polydipsia, dense hair growth, etc.), that treatment is prescribed before testing takes place.

The earlier the symptoms are recognized and treated the better the results are. Once a horse is already suffering from severe symptoms such as repeated foundering and multiple infections, relief from drugs is minimal. While there are drugs for treating the symptoms, they do not treat the pituitary tumor itself. The tumor will continue to grow until it compromises the horse's quality of life. There are currently no methods of removing or curbing the growth of the pituitary tumor.

No treatment for Cushing’s will cure the disease. Therefore, the owner’s role will be to focus on Careful Health Management and Preventive Treatment as follows:

	Avoid stressing the horse. The hormones tell the body it is already stressed.
	Sticking to a strict routine, which will help minimize stress.
	Keeping water and feed conveniently located and in the same place.
	Clipping the horse in warm weather; using blankets when it is cold.
	Keeping up grooming to minimize skin diseases.
	Keeping hooves in good shape.
	Checking teeth regularly and having them checked by a professional twice a year.
	Avoiding turning the horse out with aggressive horses.
	Avoiding contact with horses from a new location.
	Keeping immunizations up to date/ making sure all necessary shots are given.
	Deworming regularly (usually every 30 – 45 days).
	Providing an appropriate diet for the horse. This will usually involve elimination of simple carbohydrates.