Adaptations to daily exercise in hot and humid ambient conditions in trained thoroughbred horses.

The research examined the effects of high heat and humidity conditions on trained thoroughbred horses during and after daily exercise over a 22-day period. The study found an improved thermal and cardiovascular tolerance in horses, which can be attributed to their adaptation to these conditions over time.

Study Objectives and Methodology

• The study aimed to assess how heat and high relative humidity (RH) influences the clinical and physiological responses of horses during and after daily exercise training. It also sought to understand if repeated exposure to heat during exercise could result in increased heat tolerance or heat acclimation.
• Six trained Thoroughbred horses underwent a series of tests for 22 days, involving 1 hour of submaximal exercise in cool, dry conditions and during a 4-hour period in high heat and humidity (33-35 degrees C, 80-85% RH).
• Content measurements like rectal temperature (Tre), heart rate (HR), and respiratory rate (RR) were taken before, during, and after the exercise period. The RR was measured additionally during a 2-hour recovery period.

Key Findings

• The rate of increase in rectal temperature was higher in high heat humidity conditions, although it started to decrease significantly after the fifth day.
• The decrease in temperature was reflected in a significant decline in heat storage after exercise by day 10.
• The study observed high respiratory rates (RR) during high heat conditions, leading to decreased pre-exercise temperatures by day 10.
• The end-of-exercise heart rate was lower and didn’t change in the 1-hour before exercise, and didn’t differ significantly in high heat conditions. By day 10, the mean heart rate during the latter part of the exercise was lower than on day 1.
• Body mass did not change significantly during the 3-week period, though the decrease that occurred during the 4-hour training period was significantly less by day 15.
• Over the study period, water consumption increased largely due to a two-fold increase in water intake during the heat exposure period.

Summary of Study

• The study concluded that 3 weeks of daily exposure to, and exercise in, hot and humid ambient conditions resulted in a progressive reduction in thermal and cardiovascular strain. It suggests that the physiological adaptations observed in the horses are consistent with improved thermal tolerance or heat acclimation.