Effect of heat acclimation training frequency on the physiological adaptations of Thoroughbred horses.

The research article explores how different frequencies of heat acclimation training can influence physiological adjustments in Thoroughbred horses. It concluded that both daily and intermittent training strategies improve horse thermoregulation and cardiovascular function, but the specific outcomes and advantages differ between the two methods.

Research Design

• The study was a randomized crossover study that investigated the effects of two different heat acclimation protocols with eight trained Thoroughbred horses. The protocols under analysis were consecutive acclimation (nine consecutive days of heat exposure) and intermittent acclimation (three days a week for three weeks of heat exposure).
• As part of both regimens, the horses engaged in 30 minutes of exercise in hot conditions, with a Wet Bulb Globe Temperature (WBGT) of 30°C. A WBGT is a measure of the heat stress in direct sunlight, which takes into account temperature, humidity, wind speed, sun angle, and cloud cover.
• Prior to and following the heat acclimation, the horses participated in incremental exercise tests.

Measurements and Assessments

• The research team assessed a variety of physiological effects including pulmonary artery temperature, cardiovascular function, blood gases, plasma lactate, and the expression of heat shock proteins (HSP) in the horses’ skeletal muscle.

Key Findings

• Both protocols led to a decrease in resting temperature and an increase in the velocity at which pulmonary artery temperature reached 40°C.
• Both protocols resulted in improved time to exhaustion, with the intermittent regimen showing a slightly higher improvement.
• Markers of enhanced aerobic performance were noticeable, including increased maximal oxygen consumption (V̇O2 max), the speed eliciting maximal oxygen consumption, and maximum heart rate.
• The consecutive protocol showed a higher improvement in maximal stroke volume (the amount of blood ejected from the heart in one heartbeat) and a greater reduction in body weight compared to the intermittent protocol.
• On the other hand, the intermittent heat acclimation resulted in a higher increase in the expression of HSP70 – a protein that aids in stress resistance and recovery.

Implications and Conclusion

• The research clarifies the different impacts of consecutive and intermittent heat acclimation on Thoroughbred horses, both revelations beneficial in physiological adaptation.
• The differences seen in cardiovascular responses, body weight reduction, and HSP70 expression between the two methods may guide the optimization of training strategies for maximizing the performance of racehorses in hot conditions.