Heat storage in horses during submaximal exercise before and after humid heat acclimation.

The research investigates how acclimating Thoroughbred horses to hot and humid conditions affects their body’s heat regulation during exercise. It found that while heat acclimation provides some benefits, it does not significantly affect heat storage or exercise duration in very high heat environments.

Methodology

• The study involved six exercise-trained Thoroughbred horses that underwent 21 days of heat acclimation. This involved performing moderate-intensity exercise in a controlled environment with high heat and humidity (34.2-35.7 degrees Celsius and 84-86% humidity).
• Exercise tests were carried out in different environmental conditions – cool and dry, hot and dry, and hot and humid. This was done at the beginning of the acclimation period and then on several key days throughout the period.
• The horses’ peak oxygen uptake, pulmonary arterial temperature, and rectal temperature were monitored during the tests.
• The ratio of required to maximum evaporative capacity for each environment was also measured.

Findings

• The study found a drop in both the horses’ arterial and rectal temperature around halfway through the acclimation period.
• However, this did not result in any noticeable change in exercise duration or rate of heat storage when exercising in hot and humid conditions.
• In hot and dry conditions, the horses were able to exercise for a longer duration, and the increase in arterial temperature was slower, indicating decreased heat storage.
• The research concludes that while heat acclimation can provide some advantages, such as reduced heat strain in hot and dry conditions, it does not offer significant benefits in conditions of uncompensable heat stress, where the required evaporative capacity is notably higher than the maximum.

Implications

• This study contributes valuable insights into the thermoregulatory responses of horses during exercise in various environmental conditions.
• It is particularly useful for developing training and care procedures for racehorses or other working horses that might be exposed to varying temperatures and levels of humidity.
• The clear decline in heat-related advantages as the difference between required and maximal evaporative capacity increases also suggests potential limits to the effectiveness of heat acclimation.