Equine Cushing's Disease & Pregnancy

Biological Effects

• Equine Cushing's disease results from the growth of a benign tumor on or near the pituitary gland, in the region known as the pars intermedia. According to The Horse website, the tumor causes over-stimulation of adrenal glands, releasing adrenocorticotropin hormone (ACTH), beta-endorphin, melanocyte-stimulating hormone and corticotropin-like intermediate peptide. These hormones result in high levels of cortisol circulating throughout the animal's body. Often known as pituitary pars intermedia dysfunction, or PPID, Cushing's disease is also referred to as hyperadrenocorticism and pars intermedia pituitary adenoma.

Symptoms

• The most prevalent symptom of equine Cushing's disease is the growth of a long body hair. In most cases, it first appears as if the horse simply did not shed its winter coat. The growth of the hair will continue until it is long, thick and curly, a condition referred to as hirsutism. According to Dr. Siddra Hines in "Equine News," Cushing's disease is the only cause for abnormally long hair growth.

  Horses with Cushing's will develop a pot-bellied appearance that may be mistaken for pregnancy. The weakening of abdominal muscles in combination with the accumulation of fat gives the horse a pregnant appearance.

  Cushing's disease causes the loss of body weight and muscle. However, the increased cortisol results in odd accumulations of fat around the eyes, at the tail base and in random areas.

  Many horses with Cushing's suffer from laminitis, infections and slow healing.

Testing

• Various tests exist for equine Cushing's disease. Veterinarians frequently perform the dexamethasone suppression test in the field. However, the dexamethasone test is known for giving false positive results in the fall months. The domperidone response test is harder to perform in the field and requires several days. ACTH and insulin levels may be tested as they are generally elevated when a horse has equine Cushing's.

  Due to cost restrictions, many horses are diagnosed based upon the presentation of symptoms.

Treatment

• No cure exists for equine Cushing's disease. Veterinarians aim to treat the symptoms in order to extend the life of the animal. A variety of drugs are used to decrease hormone levels. Serotonin blockers and steroid inhibitors are often used to suppress hormones or help with resulting anorexia and depression.

  Horses with Cushing's must be body clipped regularly to prevent overheating. The animal must be watched carefully for any wounds or infections. The Horse website recommends routine farrier appointments, dental screenings, vaccinations and frequent dewormings.

  Dietary needs change for horses with equine Cushing's disease. Carbohydrates should be decreased in order to help balance insulin. The risk of laminitis increases in insulin-resistant horses with high blood glucose levels.

Pregnancy

• Most animals afflicted by equine Cushing's disease are not able to conceive due to the imbalance of hormones in the body. Those that do conceive often will not deliver a live foal. Many mares will produce milk even though they are not pregnant, due to hormones in the blood. Veterinarians recommend that horses with equine Cushing's disease be kept in situations where they are not subject to breeding. In rare cases, otherwise healthy mares with Cushing's have delivered healthy foals.

Prognosis

• Horses with equine Cushing's may live approximately five to seven years, according to The Horse website. The willingness of the owner to take appropriate measures on behalf of the animal extends the animal's life. However, quality of life may be diminished due to laminitis and infections. Once the tumor reaches a large size, seizures and blindness occur.