Clinical and Laboratory Diagnosis of Endocrine Disorders in Horses

The most common endocrine disorders of horses are pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS). Although hypothyroidism is also suspected and treated in many equids, clear documentation this syndrome has rarely been described in horses and it is often confused with EMS. Pituitary pars intermedia dysfunction (PPID): PPID, also known as Equine Cushing’s disease, is the most common endocrinopathy of equids. PPID increases in prevalence with age and may affect 15-20% of equids over 15 years of age and hair coat changes, consistent with PPID were recently reported in nearly 40% of equids (mostly ponies) over 30 years of age. There is no apparent sex or breed predilection; however, PPID is more common in ponies than horses. Cushing’s disease in horses develops consequent to hyperplasia or adenoma formation in the pars intermedia that appears to be due to loss of dopaminergic hypothalamic innervation. Abnormal pars intermedia cells, melanotropes, produce excessive amounts of pro-opiomelanocortin (POMC) and a number of POMC-derived peptides including immunoreactive adrenocoticotropin (ACTH) peptides, although the ACTH peptides may not all be bioactive. [...]