Body weight, fluid, electrolyte, and hormonal changes in horses competing in 50- and 100-mile endurance rides.

The research study investigated the effects of prolonged exercise on horses, specifically focusing on fluid and electrolyte losses during 50- and 100-mile endurance competitions. The findings revealed that despite a general return-to-normal of plasma volume and ionic composition following the recovery period, a substantial depletion of body fluid and electrolyte stores still remained.

Research Methodology

• The study involved observing changes in body weight, PCV, serum osmolality, plasma total protein, lactate, aldosterone, and serum electrolyte concentrations, and exchangeable cation content in 12 horses participating in 50-mile endurance rides and 7 horses in 100-mile rides.
• The horses’ body weight was measured through a portable load bar scale, and blood samples were collected at different stages: before the start of the ride, at the end of the ride, and after approximately 2 and 18 hours of recovery for horses in the 50-mile ride. For those in the 100-miles rides, additional measurements were taken during the ride (after 50, 67, and 84 miles) and after about 12 hours of recovery.

Results and Findings

• The study noted an average decrease of 3.6% and 4.9% in body weight in horses successfully completing the 50 and 100-mile endurance rides, respectively. Post-recovery, the body weights were lower than their preride values by 4.3% (50-mile ride) and 3.9% (100-mile ride).
• The study found an increase in plasma total protein concentration, indicating a decrease in plasma volume during the ride. However, these measurements returned to preride values after the recovery period.
• There were decreases in serum osmolality and serum electrolyte concentrations but an increase in aldosterone concentration during the exercise. The aldosterone concentration further increased during recovery to peak levels.

Conclusions

• The study concluded that despite the apparent quick recovery of plasma volume and ionic composition close to normal values, there was a significant depletion of body fluid and electrolyte stores persisting after the recovery period in horses successfully completing the 50- or 100-mile endurance competition.