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.
BACKGROUND
Hyperhydration, prior to prolonged moderate-intensity exercise simulating the 2nd day of a 3-day equestrian event (E3DEC), may induce arterial hypoxaemia detrimental to performance.


OBJECTIVE
Because moderate-intensity exercise does not induce arterial hypoxaemia in healthy horses, the effects of pre-exercise hypervolaemia on arterial oxygenation were examined during a prolonged exercise protocol.


METHODS
Blood-gas studies were carried out on 7 healthy, exercise-trained Thoroughbred horses in control and hyperhydration experiments. The study conformed to a randomised crossover design. The sequence of treatments was randomised for each horse and 7 days were allowed between studies. Hyperhydration was induced by administering 0.425 g/kg bwt NaCl via nasogastric tube followed by free access to water. The exercise protocol was carried out on a treadmill set at a 3% uphill grade and consisted of walking at 2 m/sec for 2 min, trotting for 10 min at 3.7 m/sec, galloping for 2 min at 14 m/sec (which elicited maximal heart rate), trotting for 20 min at 3.7 m/sec, walking for 10 min at 1.8 m/sec, cantering for 8 min at 9.2 m/sec, trotting for 1 min at 5 m/sec and walking for 5 min at 2 m/sec.


RESULTS
NaCl administration induced a significant mean +/- s.e. 15.5 +/- 1.1% increase in plasma volume as indicated by a significant reduction in plasma protein concentration. In either treatment, whereas arterial hypoxaemia was not observed during periods of submaximal exercise, short-term maximal exertion caused significant arterial hypoxaemia, desaturation of haemoglobin, hypercapnoea, and acidosis in both treatments. However, the magnitude of exercise-induced arterial hypoxaemia, desaturation of haemoglobin, hypercapnoea, and acidosis in both treatments remained similar, and statistically significant differences between treatments could not be demonstrated.


CONCLUSIONS
It was concluded that significant pre-exercise expansion of plasma volume by this method does not adversely affect the arterial oxygenation of horses performing a prolonged exercise protocol simulating the 2nd day of an E3DEC.
Tennent-Brown
B S
BS
Department of Veterinary Clinical Medicine and Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61802, USA.
Goetz
T E
TE
Manohar
M
M
Hassan
A S
AS
Freeman
D E
DE
Bundy
J S
JS
Evans
M R
MR
D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary*; D001810:Blood Volume / Q000502:physiology / Q000662:veterinary*; D018592:Cross-Over Studies; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D006454:Hemoglobins / Q000378:metabolism; D006736:Horses / Q000097:blood / Q000502:physiology*; D008297:Male; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology*; D013997:Time Factors
D006454:Hemoglobins; D012965:Sodium Chloride; D010100:Oxygen