Body weight,hematologic findings,and serum and plasma biochemical findings of horses competing in a 48-, 83-, or 159-km endurance ride under similar terrain and weather conditions

OBJECTIVE: To compare physiologic, hematologic, and selected serum and plasma biochemical variables obtained from horses competing in 48-, 83-, or 159-km endurance rides before competition and at the same cumulative distance points. ANIMALS: 83 horses. PROCEDURE: Weight and rectal temperature measurements and blood samples were obtained from horses before, during, and after 1 of 3 rides conducted on the same day. Plasma protein (PP), lactate, WBC, serum electrolyte, and calcium concentrations; PCV; and creatine kinase (CK) activity were determined. Assessments were made to determine whether any differences among groups, with respect to total distance competed, could be explained by differences in lap speed or conditioning and to investigate the effect of time in transit or on-site prior to competition on results of blood analyses or competition outcome. RESULTS: Horses in the 159-km distance group had the lowest preride serum sodium, chloride, bicarbonate, and calcium concentrations. As hours in transit increased, preride PP concentration was significantly greater; serum sodium, chloride, and bicarbonate concentrations were lower; CK activity at 159 km was greater; and horses were more likely to be eliminated. The preride sodium was significantly greater in horses that completed the ride, compared with those eliminated. CONCLUSIONS AND CLINICAL RELEVANCE: Among distance groups, distance ridden, speed, level of fitness, and years of experience of horses had little effect on the variables examined. Electrolyte and water supplementation and earlier arrival at the event may be beneficial for horses that are transported long distances to endurance competition.