Hyperhydration prior to moderate-intensity exercise causes arterial hypoxaemia.

Area of Science:

• Equine physiology
• Sports science
• Veterinary medicine

Background:

• The second day of a 3-day event is physically demanding for horses.
• Hot and humid conditions can exacerbate dehydration, negatively impacting cardiovascular and thermoregulatory function, and exercise capacity.
• Exercise-induced dehydration is a significant concern in equine athletic performance.

Purpose of the Study:

• To investigate the effects of pre-exercise hyperhydration on plasma volume, core temperature, and exercise capacity in horses.
• To test the hypothesis that fluid administration would increase plasma volume and limit core temperature increases.
• To evaluate the impact of hyperhydration on cardiovascular and respiratory function during simulated competition.

Main Methods:

• Seven Standardbred geldings underwent a standardized training protocol and exercise test.
• Horses were subjected to a 4-phase exercise test designed to elicit specific heart rate percentages.
• A cross-over design was used, with horses receiving either no fluid (control) or approximately 26L of isotonic fluid via nasogastric tube 120 minutes prior to exercise.

Main Results:

• Hyperhydration led to a pre-exercise bodyweight gain of 21.3 +/- 1.2 kg.
• Horses in the hyperhydrated group experienced greater arterial hypoxemia during intense exercise phases (B and D).
• Lower pH and HCO3- levels were observed in both arterial and mixed venous blood of hyperhydrated horses.

Conclusions:

• Pre-exercise hyperhydration in horses may induce pulmonary edema, leading to more severe arterial hypoxemia during intense exercise.
• The administration of large fluid volumes prior to exercise can be detrimental to respiratory function in horses.
• Caution is advised when administering large fluid volumes to horses before strenuous exercise to avoid adverse effects.