Horse Cushing's Disease 101: Causes, Symptoms and Recovery

Once horse Cushing’s disease was called old horse’s disease. Now it is called by veterinarians and concerned horse owners under a variety of names, including pituitary pars intermedia dysfunction (PPID), hyperadrenocorticism, Cushing’s syndrome and equine Cushing’s disease (ECD.)

It most commonly develops in very old horses of around years old. However, horse Cushing’s disease can appear in horses or ponies as young as seven. There are similar conditions called Cushing’s disease in dogs and in people. But medications or surgeries for dogs or people with Cushing’s disease should never be used on horses.

What Is Horse Cushing’s Disease?

Horses with Cushing’s disease start with the same symptoms:

  • Drinking and sweating far more than usual;
  • Urinating far more than usual because of increased thirst;
  • Becomes exhausted far more quickly than usual;
  • Weight loss, especially along the backbone and over the eyes;
  • Appearance of a swayback or pot belly – and in some rare cases, both!
  • Drastic change in a horse’s coat. It becomes long, wavy and even curly. It does not shed in warmer weather, making the horse appear scruffy and ill-kempt, despite regular grooming.

Other less frequent symptoms of horse Cushing’s disease are:

  • Constantly comes down with breathing problems;
  • Picks up intestinal worms, especially pinworms, even when regularly wormed;
  • Mares stop coming into season;
  • Mares suddenly produce milk even though they are not pregnant or are very early in a pregnancy;
  • Horse more prone to getting infections and ulcers in the mouth, hooves, tendons or sheath;
  • Wounds take much longer to heal than usual.

If the horse is not treated for Cushing’s then it will soon die. Fortunately, horses and ponies can be successfully treated and wind up living many more years.

What Causes Horse Cushing’s Disease?

Old horse’s disease was a mystery until a surgeon named Henry Cushing discovered the cause in human brains. It turned out that the cause in humans is also the same cause in dogs and horses. This is a non-cancerous tumor growth in the pituitary gland. Located at the base of the brain, the pituitary gland is responsible for making many important hormones that regulate a horse’s body functions.

However, the tumor causes the pituitary gland to flood a horse’s body with a particular hormone. A horse or pony with Cushing’s disease has far too much pro-opiomelanocortin (POMC). This hormone helps an animal deal with stress. Healthy horses and ponies only need small doses. Just why this tumor develops is unknown.

Treatment Options Available for Horse Cushing’s Disease

If caught early before complications like heavy worm infestation, respiratory disease or tooth loss develop, treatment for horse Cushing’s disease is often successful. First the horse or pony needs a blood test and an insulin test to make sure the problem is Cushing’s and not anything else.

The treatment is then two-faceted. The first facet is medication and the second is improving the horse’s diet. Medication aims to regulate brain chemistry in similar ways that antidepressants help regulate brain chemistry in people. The most popular medications for horse Cushing’s disease include:

  • Pergolide mesylate (sold in America under the brand name Permax). It is given in tablets which are crushed and mixed with molasses.
  • Cyproheptadine, a rather inexpensive serotonin blocker also available in tablets.
  • Bromocriptine mesylate (brand name Parlodel) which is an injectable drug often used if the first two drugs prove ineffective.

Many medications doses can reduce when the horse or pony stops drinking so much. Turn off all automatic waterers in stalls of affected animals. Use buckets to be sure of the amount of water an animal drinks a day.

Diet Changes

Dietary changes include restricting the number of calories eats in a day and putting on a muzzle for sick horses turned out in pastures rich in sweet grass. Gradually switch the horse from its usual grain feed to a lower-calorie feed. Changing suddenly may cause colic. Avoid feeding rye grass, fescue and bromegrass hays. These are too rich for horses or ponies suffering from Cushing’s disease. Only feed hay low in nonstructural carbohydrates (NSC) of 10 percent or less.

Giving the horse or pony a close body clip (crew cut) can help make the animal look better. However, it will not prevent the coat from always growing long, wavy and scruffy.

Because the tumor that causes all the trouble is located in a marble-sized part of the equine brain, surgery to remove it is far too dangerous. Surgery is common in people and dogs with Cushing’s because their tumors are usually on the adrenal glands and not in the brain.

Preventing Horse Cushing’s Disease

Unfortunately, it is unknown how to successfully prevent a horse and especially an old pony from developing the tumor that causes Cushing’s disease. Fortunately, horses and ponies with the disease can often be brought back to health with:

  • Medications;
  • Nutritional supplements;
  • Dietary changes;
  • Large doses of TLC.

Many older horses or ponies with Cushing’s syndrome can still perform light work for many more years. Keeping a horse at a reasonable weight and getting the teeth checked twice a year for injuries can help prevent serious complications developing as a result of horse Cushing’s disease. Since horses with Cushing’s are more prone to slower wound healing, they need to be checked every day for injuries so they can be treated as soon as possible.

Summing Up

The bad news is that horse Cushing’s disease is incurable. The good news is that it is easier to treat in horses and ponies than it is in dogs and people. Horse owners that call the vet as soon as early symptoms appear and carefully follow the veterinarian’s instructions will be able to enjoy the companionship of their equine friends for many years to come.

One gray gelding diagnosed with horse Cushing’s disease was a Thoroughbred in the New Orleans Police Department named Satan’s War, a grandson of 1973 Triple Crown winner Secretariat. After an unsuccessful racing career, Satan’s War was donated to the NOPD. When he was diagnosed with Cushing’s and arthritis after 20 years of service, he was retired from the force. Yet, he went on to work with handicapped riders at a local stable.


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