Effects of shortening the steeplechase phase (Phase B) of a 3-day-event

F.M. Andrews
S.L. White
L.H. Williamson
P.L. Maykuth
Dennis R. Geiser DVM, University of Tennessee - Knoxville
E.M. Green
S.L. Ralston
R.A. Mannsman

Abstract

Of 3 groups of horses competing in the Endurance Test (Phase B) of a 3-day-event, horses in group 1 (n = 15) had a 3.5 min steeple chase phase, group 2 (n = 13) a 3 min steeple chase phase and group 3 (n = 6) a 2.5 min steeple chase phase. The shortening of Phase B was associated with a lengthening of Phase C (Roads and Tracks) so that the total distance of the event for all horses was 14 940 m. Mean ambient environmental temperature during the Endurance Test was 25.31C (20.3-29.7C). Mean relative humidity was 43.82.4% (39-48.6%) and the average 'comfort index' was 121. Blood samples were collected from the horses before and after the Endurance Test, at the 4 km marker on Phase C (C4K), at the end of Phase C, and 20 min after the completion of Phase D. There were no significant differences between the groups competing in the Endurance Test, despite the shorter Phase B. However, there were significant decreases in body weight, total body water, net exchangeable cations, chloride, ionized calcium and pH. The sodium and total calcium concentrations were not affected by the event. The packed cell volume, total plasma protein, lactate, potassium and glucose concentrations, and aspartate aminotransferase, and lactate dehydrogenase activity increased during the Endurance Test. Horses competing in the competition had significant fluid and electrolyte losses, reduced glomerular filtration, increased glycogenolysis and significant leakage of enzymes from working muscles during the competition. These changes could not be reduced by shortening Phase B and lengthening Phase C.