Repeatability of TRH Stimulation Test for Equine Pituitary Pars Intermedia Dysfunction during the Months of February through June

Abstract

Pituitary Pars Intermedia Dysfunction (PPID) is the most common endocrine disease among aged horses. Veterinarians remain challenged when diagnosing PPID unless it is an advanced case. Veterinarians rely on advanced clinical signs to be present when diagnosing, but the keys signs like hypertrichosis will not appear until the disease has reached an advanced stage. Currently, the thyrotropin-releasing stimulation test was used to aid in diagnosing early cases of the disease, but it is unknown if the test is repeatable in individual horses. It is known that the test is, however, limited to the months of February to June, as that is when ACTH levels appear to be unaffected by seasonal change. For the study, the horses had a baseline blood sample drawn followed administration of the TRH, and another sample was collected at 10 minutes post administration (T10 ACTH). The purpose of this study is to determine if the thyrotropin releasing stimulation test T10ACTH level is repeatable during the months of February through June. The results proved the test is repeatable when administered during the months of February to June.