Effect of a 14-Day Period of Heat Acclimation on Horses Using Heated Indoor Arenas in Preparation for Tokyo Olympic Games.
Authors: Munsters Carolien, Siegers Esther, Sloet van Oldruitenborgh-Oosterbaan Marianne
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Heat Acclimation in Elite Equines Four Olympic-competing horses (three event horses and one para-dressage horse, mean age 13.3 years) underwent 14 consecutive days of routine training within a heated indoor arena maintained at 32°C with 50–60% humidity, designed to simulate conditions anticipated at the Tokyo Olympic Games. Standardised exercise tests conducted on days 1 and 14 measured cardiovascular responses (heart rate), thermoregulatory capacity (rectal temperature and sweat loss), metabolic efficiency (blood lactate), and electrolyte composition of sweat (sodium, potassium, chloride concentrations). Heat acclimation produced meaningful physiological adaptations: resting rectal temperature decreased by approximately 0.1°C, heart rate during exercise fell by ~4 bpm, time to peak core temperature extended, blood lactate concentrations reduced, and three of the four horses showed decreased sweat loss alongside lower electrolyte losses. For practitioners preparing competition horses for hot climates, these findings demonstrate that effective heat acclimatisation can be achieved through standard training schedules in controlled environments, reducing thermal and cardiovascular strain without requiring specialised protocols or additional conditioning work. The extended time-to-peak temperature and improved lactate clearance suggest enhanced thermoregulatory efficiency and metabolic stability, both critical for maintaining performance and welfare during international competition in challenging environmental conditions.
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Practical Takeaways
- •Elite horses can successfully acclimate to hot climates in just 14 days using heated indoor arenas while maintaining normal training schedules—no disruption to competition prep needed
- •Heat acclimation reduces both cardiovascular strain (lower HR during exercise) and thermal stress (lower rectal temperature), which should improve performance and welfare at championships in hot climates
- •Monitor rectal temperature and heart rate responses during acclimation training as practical indicators of successful heat adaptation
Key Findings
- •Rectal temperature decreased significantly after 14 days of heat acclimation training (estimate: -0.106°C, 95% CI -0.134 to -0.078)
- •Heart rate was significantly reduced post-acclimation (estimate: -4.067 bpm, 95% CI -7.535 to -0.598)
- •Time to peak rectal temperature and heat storage increased in all horses, indicating improved thermal regulation
- •Plasma lactate concentrations decreased and sweat electrolyte concentrations (Cl-, Na+) decreased in 3 of 4 horses