Body weight, fluid, electrolyte, and hormonal changes in horses competing in 50- and 100-mile endurance rides.
Authors: Schott, McGlade, Molander, Leroux, Hines
Journal: American journal of veterinary research
Summary
# Editorial Summary Prolonged endurance exercise causes significant fluid and electrolyte depletion in horses that persists well beyond competition, according to this 1997 investigation of 12 horses completing 50-mile rides and 7 completing 100-mile distances. Researchers measured body weight, blood biochemistry (including plasma proteins, osmolality, electrolytes, and aldosterone), and fluid shifts before exercise, during the competition (at strategic intervals for the 100-mile group), immediately post-ride, and after overnight recovery. Both groups experienced substantial weight loss—3.6% for the 50-mile cohort and 4.9% for the 100-mile group—with incomplete recovery even after 18 hours of rest, retaining a 3.9–4.3% deficit compared to pre-ride values. Whilst plasma volume appeared to normalise rapidly (indicated by returning plasma protein concentrations to baseline), serum osmolality and electrolyte concentrations remained depressed, and aldosterone levels—which peaked during overnight recovery—suggested the horses' physiological systems were still actively attempting to restore homeostasis. These findings underscore the importance of structured recovery protocols, prolonged electrolyte and fluid supplementation (not just immediate post-ride provision), and extended monitoring periods for endurance horses, as conventional overnight rest alone is insufficient to restore full fluid and ionic balance despite apparent clinical normalcy.
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Practical Takeaways
- •Endurance horses require extended recovery protocols beyond overnight rest, as body fluid and electrolyte deficits persist despite apparent normalization of basic blood parameters—consider multi-day rehydration and electrolyte supplementation strategies
- •Do not rely on rapid normalization of plasma parameters as evidence of complete recovery; aldosterone elevation indicates ongoing fluid and electrolyte depletion that warrants continued monitoring and supplementation
- •Develop individualized post-ride management protocols that account for the 4-5% body weight loss inherent to endurance competition, ensuring adequate water and electrolyte intake over several days rather than assuming overnight recovery is sufficient
Key Findings
- •Body weight decreased by 3.6% after 50-mile rides and 4.9% after 100-mile rides, with persistent 3.9-4.3% deficits after overnight recovery
- •Plasma volume and ionic composition returned to near-normal values within 12-18 hours post-ride, as evidenced by normalization of plasma total protein and serum electrolyte concentrations
- •Aldosterone concentration increased during prolonged exercise and peaked after overnight recovery, indicating persistent physiological stress despite apparent normalization of other parameters
- •Substantial depletion of total body fluid and electrolyte stores persists after overnight recovery despite rapid apparent restoration of plasma volume and composition