Effects of dehydration on thermoregulatory responses of horses during low-intensity exercise.

This research investigated how dehydration affects thermoregulatory and metabolic responses in horses. Specifically, the study examined the effects during low intensity exercise and post-exercise recovery, and found that dehydration led to lower cardiac output, increased core temperatures, and decreased heat transfer from core to body surface.

Experimental Design

• The study involved six horses, which were put through exercise and recovery sessions under three conditions: normal hydration (C), isotonic dehydration induced by furosemide injection (FDH), and hypertonic dehydration caused by withholding water for 30 hours (DDH).
• The exercise was low-intensity, designed to prompt around 40% of maximum O2 consumption and lasted for approximately 40 minutes. Recovery time was monitored for 30 minutes following exercise.

Outcomes

• The research found that cardiac output, or the volume of blood the heart pumps per minute, was significantly lower when the horses were dehydrated (both FDH and DDH) compared to when they were at a normal hydration state.
• Core temperatures, measured in the middle gluteal muscle and the pulmonary artery, were higher when the horses were dehydrated (again, both FDH and DDH) than when they were normally hydrated. Moreover, there was no notable difference in the temperatures in the superficial thoracic vein and the subcutaneous sites on the back and neck or in peak sweating rates between dehydrated and normal states.

Conclusion

• Based on these findings, the study concluded that dehydration impairs the thermoregulatory system of horses, raising core temperatures and reducing the transfer of heat from the core to the periphery, i.e., body surface. This decrease in heat transfer, rather than a decrease in peripheral temperatures or reduced sweating rates, appears to explain the elevated core temperatures observed.

Implications

• The research carries important implications for the care of exercising horses. Hydration should be carefully managed to prevent impaired thermoregulation and negative impacts on the horse’s performance and wellbeing.