Josh arrived in April 2009, looking a little like a Lesser Virginia Yak. When I first saw a picture of him, I forwarded it to our vet with the note "I'm thinking Cushings." Her reply was something like "Yikes! I think your right."
When we ask our vet to evaluate or monitor a horse who has, or who is suspected of having, Cushings (more technically called Pituitary Pars Intermedia Dysfunction or PPID,) she takes a blood sample to measure the level of Adrenocorticotropic Hormone or "ACTH." Since ACTH levels naturally vary with time of year (its one hormone that increases as hours of daylight grow shorter, signally the body to prepare for winter,) we usually wait until late spring or very early summer to test.
In early June, we had a ACTH test festival, testing nine horses - 5 previously diagnosed were tested to see if their pergolide dosages were adequate, and 4 suspects. Two of the four suspicious looking horses were just grazing the upper end of the normal ACTH range. They will continue to be monitored and will be tested again next year. The other two of those four, however, Sonny and Josh, were added to the Cushings roster. As a matter of fact, Josh's numbers were not only high, they were "off the charts." We were not surprised. He did shed his yak coat in the spring, but it was immediately replaced by another winter coat. In May!
Josh was started on pergolide and within a couple of weeks, began to shed. He doesn't yet have a "normal" summer coat, but what a difference!