Comparison of three methods for estimation of exercise-related ion losses in sweat of horses.

The study focuses on quantifying the loss of fluid and ions in the sweat of Thoroughbreds undergoing low-intensity, long-duration exercise and comparing the calculation methods for estimating these losses. The findings showed that ion losses measured via calculation methods involving local sweat rate and ion composition and exchangeable cation content were comparable, while calculations using extracellular ion content derived from plasma solids led to significantly lower estimates.

Methodology

• The study was performed on 6 Thoroughbred horses that had been trained for exercise.
• The horses were set to exercise at 40% of their maximum speed that resulted in their maximum oxygen consumption for a distance of 45km.
• Stages of the experiment were segmented into three 15-km sections with each followed by a 15-minute rest period.
• The experiment was conducted twice to ensure consistency in the findings.
• The sweat of the horses was quantitatively analyzed to estimate ion losses using three different methods: sweat ion composition (SWT), net change in exchangeable cation content (CAT), and change in extracellular ion content derived from plasma total solids and ion concentrations (PLAS).

Results and Findings

• The measurement of SWT showed an average sweat fluid loss of 27.5 ± 1.6 litres over the 45km exercise period.
• The total ion loss in sweat was around 241 grams or 7.8 moles, with higher sodium losses seen in the latter two phases of exercise compared to the first phase.
• The research observed that sodium and potassium losses calculated through SWT and CAT methods were similar while ion losses calculated through the PLAS method were notably lower.

Conclusions

• The study concludes that calculations of ion losses extrapolated from local sweat rate and ion composition or from changes in net exchangeable cation content provide similar results.
• However, using changes in the extracellular ion content derived from plasma total solids and ion concentration results in underestimation of the actual ion losses.

This indicates that the measurement method can significantly impact the interpretation of how much fluid and electrolyte loss occurs during prolonged exercise in horses. Therefore, it is crucial to select an accurate method for such estimations.