Pre-exercise hypervolaemia is not detrimental to arterial oxygenation of horses performing a prolonged exercise protocol simulating the second day of a 3-day equestrian event.

The research article investigates whether pre-exercise hyperhydration impacts the arterial oxygenation of horses during a prolonged exercise simulation of a 3-day equestrian event. The findings suggest that there was no negative effect on the horses’ arterial oxygenation due to pre-exercise hyperhydration.

Research Objective and Methods

• The main objective of the study was to examine the effects of pre-exercise hypervolaemia (an increase in blood plasma volume, induced here by hyperhydration) on arterial oxygenation during a prolonged, moderate-intensity exercise routine.
• Seven healthy, exercise-trained Thoroughbred horses were the subjects of this study, structured as a randomised crossover design. Each horse was subject to both control and hyperhydration exercises, with a resting period of 7 days in between.
• For the hyperhydration part of the experiment, the horses were administered a dose of sodium chloride (NaCl) through nasogastric tube followed by access to water. This resulted in the expansion of their plasma volume.
• The exercise routine consisted of a series of walking, trotting, cantering and galloping episodes at varying speeds and durations, all performed on a treadmill set at an uphill grade of 3%.

Research Findings

• After the administration of sodium chloride, there was a notable increase (approx. 15.5%) in the horse’s plasma volume.
• Analysis showed that arterial hypoxaemia (reduced oxygen levels in the blood), haemoglobin desaturation, hypercapnoea (high carbon dioxide levels in the blood), and acidosis occurred during short-term maximal exertion in both control and hyperhydration conditions. However, during submaximal exercise periods, arterial hypoxaemia was not recorded.
• The interesting aspect here is that the degree of arterial hypoxaemia, haemoglobin desaturation, hypercapnoea, and acidosis remained the same between control and hyperhydration conditions, showing no significant differences.

Conclusion of the Study

• The study concluded that an increase in plasma volume caused by pre-exercise hyperhydration does not significantly affect arterial oxygenation in horses undergoing a prolonged exercise routine similar to the second day of a 3-day equestrian event.
• This finding refutes the original hypothesis that hyperhydration could lead to arterial hypoxaemia and thereby hinder a horse’s performance during equestrian events.