Cushing’s Disease in Horses (Equine Cushing’s Disease)

Equine Cushing’s disease occurs in horses in their later years, but recently it has been found in young horses too. This disease can be treated and horses can live a good life. This article gives more about the causes, symptoms, diagnosis, and treatment.
In 1912, Dr.Harvey Cushing discovered this disease and hence the name. Cushing’s disease can be found in dogs, horses, and even humans. Equine Cushing’s disease refers to this disease in horses. It is also referred to as ‘Pituitary Pars Intermedia Dysfunction’.

Causes

The pituitary gland, which is located close to base of brain, is a major organ of the endocrine (hormone) system. The hypothalamus is a gland located near the pituitary gland. The synergy of both these glands helps regulate the body’s system. Cortisol is a steroid hormone secreted by the adrenal glands. The hypothalamus and pituitary gland influence the production of cortisol. In Cushing’s disease, this cortisol is produced in an excessive manner, resulting in different symptoms.

The presence of a benign tumor in the pituitary gland is considered as the main cause of this disease. The tumor induces excessive secretion of cortisol. The growth of the tumor causes breakdown of the neurons in the hypothalamus, resulting in a malfunction of the hypothalamus, and hence of the pituitary gland.

Symptoms

The symptoms in horses can be noticed easily. They are as follows.

  • Excessive thirst and urination: An affected horse drinks 20 gallons of water, whereas a normal horse drinks 5-8 gallons.
  • Coat: The horse’s coat does not shed, and it becomes wavy, hard, and heavy.
  • Change in appearance: Loss in weight, dull eyes, hay belly.
  • Increased glucose level: Blood and urine contain increased levels of glucose.
  • Infections: Due to improper functioning of the immune system, the horse suffers from various infections
  • Laminitis: Older horses show symptoms of laminitis.
  • Neurological problems may arise due to increase in the size of the pituitary gland.

Diagnosis

A veterinarian will perform the following tests in case he finds the horse displaying these symptoms.

  • Blood test: This test may produce results like increased blood sugar level (120 mg/dl to 300 mg/dl) and blood fats, anemia, etc.
  • Urinalysis: It may reveal Glycosuria and ketonuria (very high level of glucose and ketones in urine).
  • DST- Dexamethasone Suppression Test: There are two steps involved in this test. First, a blood sample is taken to determine the level of cortisol. Then, dexamethasone is injected. The dexamethasone suppresses the adrenal gland to secrete less cortisol. A blood sample is taken again after 24 hours. Both samples are compared to check the change in the level of cortisol. In normal horses, there is a marked reduction, whereas affected horses show very less reduction. This test is most commonly used by vets to detect the disease. A new method, which involves a combination of DST with TRH (thyrotropin releasing hormone) stimulation test is now carried out.
  • ACTH stimulation test: This is another method of testing cortisol levels. One unit of ACTH is injected per kg of body weight. Affected horses show a four times rise in cortisol, while normal horses show only a doubled rise. This test is not that reliable when compared to others.

Treatment

If this disease is detected at an early stage, it is possible to give the horse a proper treatment. However, the treatment has to be continued for life. Various drugs which help to reduce the cortisol levels are used. These drugs are expensive. Given below are some methods to help a horse suffering from this disease live a comfortable life.

  • The coat should be trimmed in summer since the horse is unable to shed it.
  • If the horse has skin infections, use of an antibacterial gel is recommended.
  • The blood test may help in deciding the diet of the horse so as to avoid an increase in sugar level.
  • Proper dental care and vaccinations are a must.

Trials were conducted to give a herbal treatment to such horses. Haste berry (Vitex agnus castus) was found effective when used in the early stages of the disease. The horses who were given this herbal treatment showed improvement in a short span of 3 weeks.

Equine Cushing’s disease can be easily noticed and is treatable. Though it cannot be cured, the affected horse can lead a normal life if given proper treatment.