IntroductionExercising horses one, two, or three times per week during 6 weeks using two intervals with near‐maximal speed over 100 m elicited a decrease of VLa4, a widely accepted parameter of fitness and competitive success of horses (speed at which, under defined conditions, the blood lactate concentration reaches 4 mmol/l). Therefore, two field studies were performed to examine the possibility of avoiding decline in VLa4 with this type of exercise.MethodsStudy 1) 6 horses were submitted to the same exercise as above once per week during the first 2 weeks of a conditioning period (CP) adding one interval in each exercise session every 2 weeks for the following 6 weeks. Study 2) 6 horses did the same as horses in study 1 plus once per week an exercise bout at their individual VLa2 during 35 minutes. Before, every 2 weeks during, and 2 weeks after the CP, horses were subjected to standardized exercise tests to determine their VLa4 (and VLa2 where convenient) and maximal speed (speedmax). The effect of conditioning on VLa4 and speedmax was examined using two‐way repeated measures analysis of variance and Fisher's test.ResultsIn study 1 mean VLa4 declined during the first 4 weeks of CP but increased to the initial level thereafter (P<0.05) while speedmax remained the same over time. In study 2 VLa4 decreased continuously (P<0.01) while speedmax increased (P<0.01).ConclusionsThe results might be important to train horses racing over different distances.Ethical Animal ResearchAll procedures were approved by the Bioethical Committee of the University Nacional del Litoral, Esperanza, Argentina. Sources of funding: Verein zur Förderung der Forschung im Pferdesport, Germany, AVIGAN Alimentos Balanceados and Pellfood. Competing interests: none.