Effects of Competitive ELISA-Positive Results of Piroplasmosis on the Performance of Endurance Horses

SIMPLE SUMMARY: Equine piroplasmosis (EP) is a common infectious disease in southern Europe. To better understand the impact and influence of EP on the performance of endurance horses, we collected blood samples from national elite horses during different endurance competitions. The horses were tested against piroplasmosis, and several blood parameters related to performance were also evaluated. It seems that horses without clinical signs of piroplasmosis can participate without performance impairment in competitions of up to 80 km. Although it is recommended that longer distance competitions should be further evaluated, this is the first step for decision-making by organizers and participants in this sport. ABSTRACT: Endurance is an increasingly popular equestrian sport. However, in southern Europe, there is a high prevalence of horses that are asymptomatic carriers of equine piroplasmosis (EP), a tick-borne disease that could affect their performance. This study aimed to evaluate the impact and influence of EP on the performance of endurance horses. Blood samples were collected from 40 horses in Extremadura, Spain, before and after a race, in different national elite horse endurance competitions. Hematological and biochemical parameters and EP seroprevalence were analysed by competitive enzyme-linked immunosorbent assay. The global seroprevalence of EP was 70%, with 27 horses testing positive for Theileria equi (67.5%) and three (7.5%) for Babesia caballi, with two of these horses (5%) positive for both. Approximately 82.5% of the horses (33 of 40) completed the competition, with no influence on performance or position achieved in those with subclinical parasitosis. There were also no significant differences in hematological or biochemical values between seropositive and seronegative horses. The data suggest that horses without clinical signs of EP can participate without performance impairment in competitions of up to 80 km. Although it is recommended that longer distance competitions should be further evaluated, this is the first step for decision-making by organizers and participants in this sport.