Reasons for performing study: This study investigated the physiology of endurance horses competing in warm weather over technical terrain, a situation where horses may become metabolically compromised.
Hypotheses: There will be changes in physiological, haematological and biochemical variables as horses progress through the 160 km ride and horses detected clinically at the veterinary inspections as metabolically compromised will have significant differences in measured laboratory variables compared to horses that complete the ride successfully.
Methods: Forty-eight horses competing in the Australian Tom Quilty 160 km endurance ride were monitored and weighed, and blood samples collected for analysis of electrolytes, packed cell volume (PCV), plasma protein and acid-base variables, preride, mid-ride, at the end of their ride and the following morning after a period of recovery. Statistical analysis was performed using multinomial logistic regression and repeated measures ANOVA.
Results: Of the 48 horses participating in the study, only 18 successfully completed the ride (SC), 16 were eliminated for lameness (VOL) and 10 for metabolic reasons (VOM); 4 were voluntarily withdrawn by the riders. A lighter preride bodyweight was predictive for VOM. PCV and total plasma protein increased mid-ride in all groups compared to preride, with significantly greater increases in PCV for VOM compared to the other horses. Changes were detected in blood concentrations of sodium, chloride and calcium over time and between the groups, with lower mid-ride sodium and chloride in VOM compared to SC and VOL.
Conclusions: VOM horses weighed less preride and were, on analysis of blood and physiological variables mid-ride, more dehydrated with greater electrolyte depletion than the SC or VOL horses.