Circannual variation in plasma adrenocorticotropic hormone concentrations and dexamethasone suppression test results in Standardbred horses, Andalusian horses and mixed-breed ponies

Abstract

Objective To compare circannual plasma concentrations of adrenocorticotropic hormone (ACTH) and seasonal dexamethasone suppression test (DST) results between three different equine breed groups. Methods Six Standardbred horses, six Andalusian horses and six mixed-breed ponies were followed over a 1-year period, during which time groups were managed identically. Blood samples were collected monthly (around the autumn equinox) or in every second month (other times of the year) for the determination of plasma ACTH concentrations using a chemiluminescent immunoassay. Overnight DSTs were performed quarterly, with suppression of plasma cortisol to below 27 nmol/L at 19 h considered a normal resul..