Attention Owners of Cushing’s Horses Diagnosed by TRH Response Test 

Eleanor M. Kellon, VMD

Some horses with Cushing’s/PPID have normal levels of the hormone ACTH but test positive with a TRH stimulation test.

How can you monitor their response to medication when ACTH is normal to start with?

Testing adrenocorticotropic hormone (ACTH) levels is the usual way Pituitary Pars Intermedia Dysfunction (PPID) is diagnosed, but it’s not always accurate. Many early cases, and even some advanced cases, do not have abnormal levels of ACTH detected.

We have learned a lot about early PPID, where signs like fall laminitis later in life and unexplained tendon or ligament disease, can be signs long before the classical long curly coat and muscle loss. There are even some cases with those late classical signs that do not have high ACTH. We can diagnose those horses with a Thyrotropin-Releasing Hormone (TRH) Response Test.

TRH stimulates the intermediate lobe of the pituitary gland, resulting in abnormal levels of ACTH after TRH administration in positive horses.

Once diagnosed, the horse will be treated with pergolide, but how do you make sure the dosage is correct and doing its job? We can’t use ACTH since that was normal before treatment. It makes sense that the TRH response would improve or normalize, but information on changes after treatment is limited.

The nonprofit Equine Cushing’s and Insulin Resistance Group Inc,, wants to change that. They are offering $300 to offset testing costs to anyone with a PPID horse diagnosed by TRH testing who will repeat the test after the horse has been on pergolide for at least 3 weeks.

If your equine has had a positive TRH test and has been on pergolide for three weeks, contact Dr. Kellon at

About ECIR Group Inc.
Started in 1999, the ECIR Group is the largest field-trial database for PPID and EMS in the world and provides the latest research, diagnosis, and treatment information, in addition to dietary recommendations for horses with these conditions. Even universities do not and cannot compile and follow long term as many in-depth case histories of PPID/EMS  horses as the ECIR Group.

In 2013 the Equine Cushing’s and Insulin Resistance Group Inc., an Arizona nonprofit corporation, was approved as a 501(c)3 public charity. Tax deductible contributions and grants support ongoing research, education, and awareness of Equine Cushing’s Disease/PPID and EMS.

THE MISSION of the ECIR Group Inc. is to improve the welfare of equines with metabolic disorders via a unique interface between basic research and real-life clinical experience. Prevention of laminitis is the ultimate goal. The ECIR Group serves the scientific community, practicing clinicians, and owners by focusing on investigations most likely to quickly, immediately, and significantly benefit the welfare of the horse.

Contact:  Nancy Collins

Stock photo available