Effects of administration of water versus an isotonic oral rehydration solution (ORS) at rest and changes during exercise and recovery.

This study assessed how horses react to either water or an isotonic oral rehydration solution (ORS) in terms of hydration and exercise performance. It turns out that an isotonic, plasma-like ORS significantly aids in maintaining plasma volume and circulation at rest, as compared to pure water.

Research Methodology

In the study, two hydration methods were administered to five thoroughbred horses: an isotonic oral rehydration solution (ORS) that simulates the osmotic balance of plasma, and regular water, which lacks an osmotic skeleton. These solutions were administered via nasogastric tube four hours post-feeding. The experiment consisted of four separate sessions in which the horses were either rested or exercised.

• The effects of each hydration method were then assessed based on a series of measurements taken at rest, during exercise, and after exercise.
• These measurements included the uptake of deuterium (an isotope of hydrogen used to measure body water), the concentrations of sodium, potassium, chloride, glucose, total protein in the plasma, volume of packed cells, pH values, and CO2 levels.
• The researchers also measured the actual and standard base excess, changes in plasma volume, and any weight loss.

Observations and Findings

• An increase in the plasma uptake of both water and ORS was observed by 10 minutes post-administration.
• Interestingly, there were no significant differences in the rate of uptake of water or ORS while the horses were at rest. However, during the exercise session, there was a trend toward slower absorption of the ORS compared to water.
• The mean decrease in total protein (3.0 g/l) and the increase in plasma volume (4.6 ml/kg) after administering ORS while resting was significantly higher as compared to water. Corresponding values after administering water were a decrease in total protein by 1.3 g/l and a decrease in plasma volume by 1.2 ml/Kg.
• There was no significant difference in total plasma protein or plasma volumes detected after either water or ORS administration during the exercise treatment.
• Exercise seemed to have minimal impact on plasma sodium concentration.

Conclusions

The research findings established the effectiveness of isotonic, plasma-like ORS in the maintenance of plasma volume and circulation better than equal amounts of water when given at rest. However, the positive effects observed upon administration of ORS at rest might be somewhat masked during exercise. As such, the choice of hydration method for equine athletes may need to be adjusted depending on the stage of activity (rest vs. exercise).