Hydration effects on physiological strain of horses during exercise-heat stress.

The study investigates how varying hydration methods can impact horses’ physiological response during strenuous exercise in hot conditions. It found that maintaining hydration significantly reduced negative effects of exercise-induced dehydration and heat stress.

Research Aim and Methodology

The aim of the study was to explore how differing hydration methods – hyperhydration, exercise-induced dehydration and oral fluid replacement – could affect the physiological reactions of horses during periods of intensive exercise in a hot environment.

To perform the study, six horses were put through a 90-minute exercise regimen and repeated this process three times under different hydration conditions. The regimen consisted of two 45-minute exercise periods, with a 15-minute recovery phase in between. In a randomized order, the horses either received no fluid, 10 liters of water or a carbohydrate-electrolyte solution both two hours before the exercise protocol as well as in-between the two exercise periods.

Findings related to Hyperhydration

The study revealed that:

• Hyper-hydrating the horses before exercise, either with water or a carbohydrate-electrolyte solution, did not produce any significant changes in heart rate, cardiac output, stroke volume, core body temperature, sweating rate or sweating sensitivity during the initial exercise period.

Findings related to Dehydration

Related to exercise-induced dehydration:

• By the end of the second exercise period, horses that did not receive fluids showed a greater decrease in body weight indicating exercise-induced dehydration, leading to greater heat storage and core body temperature approximately 1.0 degrees Celsius higher than the other two groups (who had received water or carbohydrate-electrolyte solution).
• Further, these dehydrated horses showed significant decreases in cardiac output, stroke volume, sweating rate, and sensitivity to sweat.

The Effectiveness of Oral Fluid Replacement

As for the effects of oral fluid replacement:

• The researchers found that maintaining hydration (approximately 85% of sweat fluid loss) during exercise in hot conditions resulted in increased cardiac output, stroke volume, and sweating rate while reducing heat storage.
• Both water and the carbohydrate-electrolyte solution were equally effective at reducing physiological stress associated with exercise-induced dehydration and heat stress.

In conclusion, whilst pre-exercise hyperhydration offered no regulatory advantage, maintaining hydration during exercise proved beneficial in reducing physiological strain in horses. Both water and carbohydrate-electrolyte solutions proved equally effective in these circumstances.