Cushing’s disease

What is Cushing’s disease?

Equine Cushing’s disease is caused by a small benign tumour in the pituitary gland. (The pituitary, a marble-sized gland at the base of the brain, is responsible for the regulation of almost all of the body’s endocrine systems and is often referred to as a “master gland”.)

A horse with Cushing’s disease usually develops the condition in the mid to late years of life, although it is sometimes diagnosed in horses as young as seven.

What are symptoms of Cushing’s disease?

The most common symptoms of Cushing’s disease are:

  • Sudden and extreme thirst (polydipsia). An affected horse may drink as much as 80 litres of water a day (as opposed to an average 20 – 30 litres). This condition is usually accompanied by excessive urination (polyuria).
  • Abnormal hair growth and shedding. Affected horses may develop a growth of heavy, coarse, often curly hair, which does not shed in the summer. This may be accompanied by sweating and seborrhea (flaking of the skin).
  • Development of a swayback stance and a pot belly.
  • Filling above the eyes caused by the deposition of fat. (Normally, you can see a depression above the horse’s eye, particularly when the horse is chewing.)
  • A depressed, sick-looking appearance with dull eyes and drab coat.
  • Increased appetite (usually with no accompanying weight gain).
  • Chronic laminitis.
  • Loss of muscle over the topline.
  • Compromised immune system. This gives rise to a host of conditions/diseases which are often passed off as old age. These include respiratory disease, skin infections, abscesses of the foot, mouth (buccal) ulcers, and periodontal disease.

Treatment for Cushing’s disease

Your veterinarian will likely use blood and urine tests to diagnose Cushing’s disease. Repeat testing may be necessary, as preliminary tests do not always produce conclusive results. Some cases of Cushing’s disease are so obvious to a veterinarian (excessive thirst, dense hair growth, etc.), that treatment is prescribed in advance of testing.

Once a positive diagnosis has been reached, appropriate treatment can begin. When symptoms are caught early, treatment can be extremely successful, returning the horse to normal health for many more years.


When deciding whether to medicate a horse with Cushing’s disease, you should first consider the cost and the condition of the horse in question. Horses with relatively mild symptoms generally respond best to medication, which may extend their useful lives by a number of years. However, a horse that is already suffering from chronic founder / laminitis and recurrent infections as a result of immune system failure will likely derive very little benefit. It is worth remembering that, while these drugs treat the symptoms, they do not treat the pituitary tumor itself. They merely treat the symptoms, and 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 equine pituitary adenomas.

Cyproheptadine (Periactin®).

This seratonin blocker is available in tablet form, which is easily absorbed into the horse’s system. A veterinarian will normally start a horse at a specific dose level (usually about 0.13 mg/kg, or about 58 mg for an average 440 kg horse), and increase it until you the clinical signs of Cushing’s disease begin to improve.

The simplest way to gauge improvement is by monitoring the horse’s water intake over a 24-hour period. This is best achieved by keeping the horse stabled and provided with water in a bucket. The dosage of medication is slowly increased until the horse’s water intake returns to normal levels (usually taking about six to eight weeks). During this time, you will likely notice that other symptoms of Cushing’s disease , such as the heavy coat and pot belly, also disappear, and the horse regains vigour and muscle tone. After this level of improvement has continued for a month, the dosage of cyproheptadine is gradually reduced until a maintenance level is reached.

Cyproheptadine is effective in about 75 – 80 percent of cases.

Pergolide mesylate (Permax®).

This drug was originally used to treat human Parkinson’s disease. At the doses considered successful in treating Cushing’s disease in humans, however, pergolide mesylate had a severe vasoconstricting effect that served to worsen the chronic laminitis that frequently accompanies Cushing’s disease. (*Note, the preceding statement refers to human use only)

In the early ‘90s, Montana equine veterinarian, Dr. Duncan Peters, decided to give a very small dose of the drug to a horse suffering from Cushing’s disease. This dose was roughly equivalent to one-sixth of the amount considered appropriate for a human. The horse responded positively. In a further study, Dr. Peters was able to duplicate the positive results in eight of nine horses/ponies with no negative side effects.

The average response time was close to three weeks, and improvement continued until the horses stabilized at an average 21 weeks. Since these results were published, pergolide mesylate has become an acceptable treatment option for Cushing’s disease.

Pergolide mesylate is usually administered orally, in tablet form. (Crushing the tablets with a little molasses is an effective way to dose your horse.)

Bromocriptine mesylate (Parlodel®) is a less popular drug used to treat equine Cushing’s disease, although still used by some veterinarians. Problems in absorption are often documented and the drug purportedly produces a number of side effects.

Herbal treatments.

While the jury is still out of the efficacy of herbal treatments for Cushing’s syndrome, there is indication that chaste berry (Vitex agnus castus) may be effective for early stage cases of Cushing’s syndrome. The UK Horse Journal ran a field trial of Vitex including 10 horses and ponies. The subjects were aged between 13 and 25 years, and were either diagnosed with Cushing’s disease or demonstrating the classical Cushing’s symptoms.

The Journal reported that typical response was “rapid and dramatic.” Shedding would typically begin within three weeks, and energy level quickly increased. High blood glucose and insulin levels dropped in some cases within four to six weeks. (The results of a later study at the University of Pennsylvania’s New Bolton Center repudiated these claims. Nonetheless, some horse owners feel that their horse was helped through use of the herb.)

Always consult your veterinarian before starting any type of treatment for your horse, including herbal remedies.

Helping the horse with Cushing’s disease

If your horse has Cushing’s syndrome, you will want to help him feel as comfortable as possible, whether or not he is receiving medication for the condition.

No treatment for Cushing’s disease will cure the disease. Therefore, your role will be to focus on careful health management and preventive treatment as follows:

  • Avoid stressing your horse. The hormonal profile of many horses with Cushing’s disease already indicates high stress levels, so reducing stress is critical.
  • Provide a safe, comfortable “sanctuary” for your horse.
  • Stick to a strict routine, which will help minimize stress.
  • Keep water and feed conveniently located and in the same place.
  • Clip your horse in warm weather; use blankets when it is cold.
  • Keep up grooming to minimize skin diseases.
  • Keep hooves in good shape.
  • Check teeth regularly and have them checked by a professional twice a year.
  • Avoid turning your horse out with aggressive horses.
  • Avoid contact with horses from a new location.
  • Keep immunizations to a minimum but make sure all necessary shots are given.
  • Deworm regularly, as recommended by your veterinarian (usually every 30 – 45 days).
  • Talk to your veterinarian about the best diet for your horse. This will usually involve elimination of simple carbohydrates.

Natural ways to help your horse with Cushing’s Disease


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Review in the prestigious Horse Journal in October and December 2003

Recovery®EQrated as “Best Performer Overall” as a pain-relieving supplement for joint pain, back pain and tendonitis – comparison of natural joint care supplements.

Review in the prestigious Horse Journal inJune 2006:

“You get what you pay for” – Horse Journal quote about Recovery®EQ used as a performance enhancing supplement – comparison of natural performance enhancing supplements

Refer to Tips for a Healthier Horse