Instructions
Test for dexamethasone suppression (DST). This is the most common and reliable test for equine Cushing's disease, but it does have a risk for false positives, according to Washington State University. This test requires two visits from the veterinarian.
Draw blood for a baseline test. The veterinarian will use this blood sample to compare cortisol levels in the second blood sample.
Inject dexamethasone into the muscle tissue. In healthy horses, dexamethasone acts on the pituitary gland to suppress the production of cortisol, a hormone. Most horses with Cushing's disease will not respond to dexamethasone due to the malfunctioning pituitary gland and will not show a decrease in cortisol levels, according to Penn State University.
Draw blood 20 hours after the dexamethasone injection. The veterinarian will send both of the blood samples to a lab to test the cortisol levels. Suppressed cortisol levels would indicate that the pituitary gland is functioning while unchanged cortisol levels may lead to a diagnosis of Cushing's disease.
Discuss other tests for Cushing's disease with your veterinarian. Additional tests for equine Cushing's disease include TRH-Response Test, which also tests cortisol levels, and the domperidone response test. These tests may be more expensive as they require additional veterinary visits.
How to Test for Equine Cushing's Disease
Equine Cushing's disease is endocrine imbalance often seen in older horses. It is also known as hyperadrenocortiscism, according to Penn State University. Horses of any breed can develop Cushing's disease, but it is seen with greater frequency in Morgans and ponies. Cushing's disease is caused by either a benign tumor growth on the pituitary gland or a breakdown of nerve cells in the hypothalamus. The most visible symptoms include a shaggy, overgrown coat, weight loss with a pot-belly and increased sweating and thirst. Equine Cushing's disease also causes lowered immune system and muscle atrophy. This disease is difficult to diagnose and has no known cure. There are tests that help identify Equine Cushing's disease.