Field evaluation of poor performance in Standardbred trotters

Exercise tests allow evaluating athletic capacity and fitness, following training-induced adaptations and determining causes of poor performance. A retrospective study was conducted over the cases of 40 poor performing Standardbreds referred to an Equine Sports Medicine consultation at a Belgian racetrack. The study aimed at determining if the implementation of a standardised exercise test and determination of specific athletic parameters could discriminate between the poor performers and a group of eight healthy racehorses and help in establishing a diagnosis. After a through clinical examination, the horses were submitted to an exercise test that consisted of 3 bouts of 1500m at increasing speeds with a recovery phase of 500 m in between. Speed and heart rate were continuously monitored and blood lactate concentrations were evaluated after each step. Pre and post-effort blood work and respiratory endoscopy with sampling were done in each horse. Five main causes of poor performance were identified: locomotor, respiratory, cardiac, muscular problems and inadequate training. In the poor performers group, 24 horses suffered from upper and/or lower respiratory disease, 20 from lameness, 4 from cardiac disease, 4 from exercise-induced myopathy and 5 from maladjusted training. More than half of the horses had multiple problems (23 horses). The fitness parameters (V-LA4, V-200) obtained were useful for inter-individual comparisons and discriminated poor performers from healthy controls, whatever the cause of the intolerance. This study confirms the high prevalence of lameness and respiratory diseases as causes of poor performance in racehorses. The field exercise tests were readily performed with minimal equipment and enabled to identify conditions which were not clearly apparent as during the clinical examination at rest. The recovery of maximum information by a thorough questioning of the trainer and selected ancillary examinations was critical to reach a diagnosis.