Post exercise hydration responses to an electrolyte, glycerol, and creatine supplement in horses: a preliminary study.

This small crossover study in six quarter horses found that a commercial hydration supplement containing electrolytes, glycerol, and creatine improved early post-exercise rehydration compared with water alone. Supplemented horses drank more, showed greater plasma volume expansion, and better maintained body mass during a 3-hour recovery.

Why this study matters

• Dehydration from sweating can impair equine performance, recovery, and thermoregulation; electrolytes are commonly used to aid rehydration.
• Glycerol and creatine are osmotically active compounds that can promote water retention in other species, but their combined effects in horses have been unclear.
• This study provides initial equine data on a commercially available supplement that includes electrolytes, glycerol, and creatine.

Study design at a glance

• Participants: Six healthy Quarter Horses.
• Design: Within-subject cross-over; each horse completed two conditions on separate study days.
• Conditions:
  • Water-only condition.
  • Supplemented condition using a commercial hydration product containing electrolytes, glycerol, and creatine.
• Protocol: Each day included a standardized moderate exercise bout, a recovery interval, and a 3-hour post-exercise hydration period.
• Outcomes assessed: Hematocrit, hemoglobin, total plasma protein, calculated plasma volume (PV), body mass change, and voluntary water intake.

Key results

• Hematocrit and hemoglobin decreased over time in both conditions, indicating post-exercise hemodilution as rehydration progressed.
• Total protein concentrations were consistently lower in the supplemented condition, consistent with greater dilution of plasma proteins.
• Calculated plasma volume increased more with supplementation than with water alone (p = 0.033).
• Body mass was preserved during the 3-hour hydration period with supplementation but declined with water only (p = 0.004).
• Horses voluntarily consumed more water when supplemented (p = 0.0079).

How to interpret the findings

• Greater plasma volume expansion and lower total protein with supplementation suggest more effective vascular rehydration during early recovery.
• Increased voluntary water intake may reflect improved palatability and/or physiologic drivers (e.g., osmolality/tonicity effects), though mechanisms were not dissected.
• Preserved body mass aligns with better net fluid balance, which is biologically plausible given:
  • Electrolytes facilitate water retention by replacing sweat losses and supporting extracellular fluid balance.
  • Glycerol can act as an osmotic agent that promotes whole-body water retention.
  • Creatine may increase intracellular water content in muscle in other species; its specific contribution in horses remains to be quantified.
• P-values indicate statistically significant differences for PV change, water intake, and body mass, but the abstract does not report effect sizes or variability.

What the study does not show

• No direct performance or thermoregulatory outcomes (e.g., heart rate recovery, core temperature, exercise capacity) were measured.
• The observation window was limited to 3 hours; longer-term hydration status, renal responses, and next-day recovery are unknown.
• Generalizability is limited: small sample (n = 6), one breed, a single exercise intensity, and unspecified environmental conditions.
• The exact supplement formulation and dosing details were not provided, so the relative contributions of electrolytes, glycerol, and creatine cannot be separated.
• Regulatory considerations (e.g., competition rules regarding ingredients) and safety over repeated use were not addressed.

Strengths and limitations

• Strengths:
  • Cross-over design reduces between-horse variability by using each horse as its own control.
  • Multiple complementary endpoints: hematologic markers, behavior (drinking), and body mass.
• Limitations:
  • Preliminary, small sample size limits precision and detection of modest effects.
  • Potential order or carryover effects and blinding/washout details are not described.
  • Palatability or flavoring effects on water intake cannot be ruled out.

Practical implications

• After moderate exercise, a combined electrolyte–glycerol–creatine supplement may help horses drink more, expand plasma volume, and better maintain body mass compared with water alone during early recovery.
• Introduce any new supplement under veterinary or equine nutrition guidance, especially for competition horses or those with medical conditions.
• Monitor individual responses (body weight, drinking behavior, urine output) when trialing such products and adjust management accordingly.
• Verify ingredient acceptability under relevant competition rules before use.

Future research directions

• Larger, randomized, blinded trials across breeds, ages, training status, and environmental conditions.
• Dose–response and component analysis to isolate the roles of electrolytes, glycerol, and creatine.
• Extended monitoring to evaluate sustained hydration, renal function, thermoregulation, and recovery over 24–48 hours and across repeated exercise bouts.
• Inclusion of performance and welfare outcomes (e.g., workload tolerance, GI comfort, behavioral indicators).
• Systematic assessment of palatability versus physiologic drivers of increased water intake.

Bottom line

• In this small cross-over study, an electrolyte–glycerol–creatine hydration supplement outperformed water alone for early post-exercise rehydration markers in Quarter Horses, supporting further confirmatory trials.