Influence of training on sweating responses during submaximal exercise in horses.

This research explores how exercise training in moderate conditions impacts the sweating response and heat dissipation in horses during exercises performed in hot conditions.

Research Context

• This study was conducted on five horses and spanned over eight weeks of exercise training five days per week in moderate weather conditions (19-21 degrees Celsius with 45-55% relative humidity).
• To replicate a hotter environment for testing the horses’ sweating response, the standardized exercise tests (SETs) were carried out under hot conditions (32-34 degrees Celsius, 45-55% relative humidity).
• The SETs comprised of a 7km run at 50% maximal oxygen consumption and were conducted at the beginning of the training period and at the end of the 2nd, 4th, 6th and 8th week (TD0, 14, 28, 42, and 56 respectively) on a treadmill inclined at 6 degrees.

Key Findings

• The primary observation was an increase in peak sweating rate (SR) during exercise after 14, 28, 42, and 56 training days, in comparison to the beginning of the training period.
• Simultaneously, SRs and sweat losses observed during recovery had decreased by the end of the 4th week (TD28).
• By the final testing day (TD56), the horses’ end-exercise rectal and pulmonary artery temperatures had reduced by around 1 degree Celsius each, indicating enhanced heat dissipation during exercise.
• Also, the mean change in body mass during the exercise test reduced by 23% from the start to the end of the training period, suggesting a decrease in total fluid loss through sweat.
• Analysis of the sweat composition showed a decrease in sodium (Na) concentration and an increase in potassium (K) concentration, while chloride (Cl) concentration remained unchanged.

Conclusions

• The study concluded that moderate-intensity training in cooler conditions led to a significantly (1.6 times) increased sweating sensitivity by the 4th week and a decrease in sweating threshold temperature by approximately 0.7 degrees Celsius after 8 weeks during exercise in hot, dry conditions.
• These altered sweat responses contributed to improved heat dissipation during exercise and a lower end-exercise core temperature.
• Another key finding was that, despite higher SRs for a particular body temperature during exercise, decreased SRs during recovery resulted in an overall reduction in sweat fluid losses. However, there was no change noted in total sweat ion losses after the training.