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Limited information exists about the physiological changes and clinical problems that occur in elite horses competing in high-speed 160 km endurance races.To provide initial data describing changes in physiological and laboratory measurements in horses competing in a high-speed, 160 km endurance race under temperate conditions and to compare data between horses that successfully completed the race and those that failed to finish.Body mass (BM) was measured, blood samples were collected, and veterinary examinations performed on horses before, during, and at the finish of a CEI*** 160 km endurance race.Of 36 horses participating in the study, 22 (61%) completed the race. Twelve horses were eliminated for lameness and 2 for persistent heart rate elevation. Mean speed of finishers was 15.2 km/h. Mean ±s.d.BM loss of finishers at the end of the race (5.7 ± 2.6%) was not different (P = 058) from BM loss of nonfinishers at elimination (6.7 ± 3.4%). Similarly, there were no significant differences in heart rate or veterinary assessment of hydration at the race end for finishers as compared to the elimination point for nonfinishers. PCV increased while sodium, chloride and potassium concentrations decreased with exercise but differences between finishers and nonfinishers were not detected. In contrast, both total and ionised calcium concentrations decreased in successful horses but remained unchanged in nonfinishers.Elite endurance horses are more likely to be eliminated from competition for lameness than metabolic problems; however, it remains unclear whether these conditions are entirely distinct. The magnitude of the decrease in sodium concentration in both finishers and nonfinishers was greater than in previous reports of 160 km rides.These data should be of use for both organisers and participants in elite 160 km endurance races. The tendency toward hyponatraemia as well as the difference in calcium concentrations between finishers and nonfinishers warrant further study.