been much research on the connection between body condition score and performance ability in horses so optimum scores are unknown. However, horses with a low body condition score lack the fat reserves for strenuous work and also may lack lean muscle. Horses with a very high body condition score carry too much weight, which interferes with stamina and biomechanics. Some studies addressed the relationship of body condition score and endurance performance in endurance races. In a study of the 1990 Purina Race of Champions (a 241-km / 150-mile, 2-day endurance race), it was found that the top-7 finishers of the race (i.e. highly competitive horses) had significantly lower body condition scores and marginally less rump fat than horses eliminated for metabolic criteria (i.e. less competitive horses). By contrast, two studies on the Tevis Cup (a 160-km / 100-mile 24-hour race held each August near Truckee, California) found both for 1995 and 1996 (study 1) and for 1998 (study 2), that significantly more horses finished the race when they had a higher (vs. lower) body condition score: Horses competing in 1995 and 1996 had body condition scores ranging from 1.5 to 5.5 (1998: 2.5 to 5.5); no horses with a score of ≤ 2.5 (1998: scores ≤ 3) finished the respective race, and all horses with a score of 5.5 (same in 1998) finished the respective race. In both studies, no significant relationship was found between the horse's weight and their time to require the course (or, if they were eliminated: the miles they completed before elimination). The studies did not find a significant effect for the influence of rider weight on the race results; for 1998, the rider weight / horse's body weight ratio was significantly higher among horses qualified for metabolic criteria than for race finishers (however no significant effect on placing of the finishers). The authors discuss for their first study the role of substrate depletion at sub-maximal exercise levels, but also the possibility that horses had a negative energy intake before the race due to their high exercise levels, possibly also leading to a decrease in muscle mass. They explain the differences of results between the studies in part in that the participating horses of the 1990 Purina Race of Champions have had to qualify before and present a more highly-performing field of horses. Both Tevis Cup studies found that horses with a higher body condition score