Signs & Symptoms of Equine Cushings Disease

Risk Factors

• Cushing's disease can affect any horse but occurs most frequently in Morgan and pony breeds. Age can also play a role, as the disease in more commonly seen in older horses. Mares, geldings and stallions are all susceptible to Cushing's.

Causes

• Cushing's disease is caused by a defect in the horse's body that causes the adrenal glands to produce too much cortisol. The adrenal gland is controlled, in part, by the pituitary gland. Most veterinarians agree the primary cause of Cushing's disease is a benign tumor in the pituitary gland.

Signs &Symptoms

• Horses with Cushing's disease are often excessively thirsty and urinate frequently. These are usually the most notable early symptoms. Muscle weakness and atrophy are also common symptoms, which sometimes lead to a Cushing's horse being swaybacked or potbellied. Muscle loss over the top line is also typical in horses affected by this disease. Sometimes horses with Cushing's show an increased appetite without any weight gain. Chronic laminitis--or inflammation of tissues in the horse's hoof--is also common in horses with Cushing's disease. Some horses will also exhibit lethargy.

  The most prevalent symptom associated with Cushing's is a change in hair coat. Owners may notice their horse is unable to shed its winter coat. This long, coarse and wavy hair is typical in horses with Cushing's disease.

  Due to cortisol's role in immune system function, horses with Cushing's disease may experience respiratory infections, skin problems, parasite infections, hoof abscesses and mouth ulcers or periodontal disease. If a Cushing's horse suffers a cut or wound, it often heals slowly.

  Another symptom noted in mares with Cushing's is an irregular estrous cycle. Sometimes the mare will not cycle at all and some horses with Cushing's become infertile. In rare instances, mares that are not pregnant may lactate.

  If the Cushing's disease is indeed being caused by a tumor, excess pressure can affect the optic nerve, leading to blindness. Other neurological symptoms include head tilting and dementia, although these symptoms are more often found with large tumors.

Diagnosis

• Diagnosis of Cushing's disease is typically done by blood test or urinalysis. These tests will indicate whether an imbalance is occurring within the horse's endocrine system and if additional hormone-specific testing is needed.

Treatment

• The good news about Cushing's disease is that it's very treatable when caught early. Cushing's horses that have pituitary gland tumors are less likely to recover, as surgery on the pituitary gland is not an option. There are two medications, pergolide mesylate (Permax) and Cyproheptadine, that have been proven effective in treating Cushing's disease symptoms in horses.