Environmental stress and 3-day eventing: effects of altitude.

The study looked at the impact of altitude on three-day event horses and concluded while the increased altitude induces physiological stress in the horses, it does not result in the same level of stress compared to that caused by extreme heat and humidity.

Overview of the research methodology

• The research was conducted with 24 horses participating in the High Prairie Preliminary and Intermediate 3-day events and Preliminary Horse Trials, held in Parker, Colorado, at an altitude of 1900 metres above sea level.
• Physical and venous blood gas data were collected from the horses, including metrics like rectal temperature, heart rate, respiratory rate, and various blood gas values (such as [K+], ionized calcium (ICa++), PCV, [Hb], PCO2, [tCO2], [HCO3-], BE, and [Na+]).

Results of the study

• The research found that despite the increased altitude, only post-exercise rectal temperature and pH were higher while the heart rate, [K+], and ionized calcium (ICa++) were lower in 3-day event horses compared to horse trial horses.
• There were no significant differences in other variables (respiratory rate [RR], PCV, [Hb], PCO2, [tCO2], [HCO3-], BE, and [Na+]).
• When compared with horses from an Arizona sea-level horse trial, Colorado horses displayed higher post-exercise heart and respiratory rates but showed lower pH, PCO2, [tCO2], [HCO3-], BE and [iCa++] values.
• This indicated that while altitude increased stress levels, it did not result in severe physiological changes or impair the horse’s ability to complete prescribed exercise tests, unlike exposure to high heat and humidity.

Conclusion of the study

• The study concluded that increased altitude does result in stress for 3-day event horses.
• However, it does not induce the severe physiological changes and inability to complete exercise tests that one observes with increased heat and humidity.
• From these and previous data, it is clear that elevated heat and humidity present more significant environmental stressors in 3-day eventing than altitude does.