Effects of cool and hot humid environmental conditions on neuroendocrine responses of horses to treadmill exercise

To determine the effects of exercise, high heat and humidity and acclimation on plasma adrenaline, noradrenaline, β-endorphin and cortisol concentrations, five horses performed a competition exercise test (CET; designed to simulate the speed and endurance test of a three-day event) in cool dry (CD) (20°C/40% RH) and hot humid (30°C/80% RH) conditions before (pre-acclimation) and after (post-acclimation) a 15 day period of humid heat acclimation. Plasma adrenaline and noradrenaline concentrations pre-acclimation were significantly increased compared with exercise in the CD trial at the end of Phases C (