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

The research explores how different environmental conditions, specifically cool and hot humid scenarios, influence the neuroendocrine responses of horses during exercise. The study particularly pays attention to concentrations of adrenaline, noradrenaline, beta-endorphin, and cortisol under different conditions and post-acclimation periods.

Study Details

• The research was conducted on five horses that completed a competition exercise test (CET) simulating the speed and endurance test of a three-day event.
• The tests were carried out under two distinctly different conditions: cool dry (20°C/40% relative humidity) and hot humid (30°C/80% relative humidity).
• The purpose was to examine significant changes in the concentrations of plasma adrenaline, noradrenaline, beta-endorphin, and cortisol resulting from these differing environmental conditions and periods of acclimation.

Research Findings

• Pre-acclimation plasma adrenaline and noradrenaline concentrations were noticeably increased in the hot, humid trial compared to the cool, dry trial after certain exercise phases and during recovery periods.
• Beta-endorphin concentrations increased at the end of certain exercise phases and recovery times during the pre-acclimation session.
• Cortisol concentrations significantly increased after the initial warm-up period and at the end of a particular exercise phase when compared to the cool, dry trial.
• The 15-day acclimation period resulted in a significant increase in plasma adrenaline concentrations after 2 minutes of recovery and an increased plasma cortisol concentration at the end of a specific exercise phase in contrast to pre-acclimation.
• Acclimation didn’t significantly influence noradrenaline or beta-endorphin responses to exercise, but there was a trend indicating lower beta-endorphin levels after acclimation at the end of certain phases and during recovery.

Conclusion and Implications

• The research concluded that exercise in cool dry conditions can increase concentrations of plasma adrenaline, noradrenaline, beta-endorphin, and cortisol, and these concentrations can be further heightened by the same exercise under hot, humid conditions.
• It was suggested that adrenaline and noradrenaline might potentially play a role in horses adapting to thermal stress.
• Changes observed in plasma beta-endorphin concentrations could potentially function as a sensitive indicator of thermal tolerance in horses both before and after acclimation.
• Plasma cortisol was not deemed a reliable specific indicator of heat stress or thermal tolerance in exercising horses, pre or post acclimation.