Impact of Lower Airway Inflammation on Fitness Parameters in Standardbred Racehorses

SIMPLE SUMMARY: Among racehorses, mild–moderate equine asthma (MEA) represents the second most frequent cause of poor performance. Multiple authors have tried to identify the direct effects of tracheal mucus accumulation and the cytological profile of the bronchoalveolar lavage (BAL) on athletic capacity, obtaining contrasting results. The present retrospective study aims to investigate the associations between different signs of airway inflammation and a series of fitness parameters obtained through a standardized incremental treadmill test in a population of 116 poorly performing Standardbred racehorses. The possible relationships between treadmill parameters and endoscopic scores, BAL leukocyte populations, and bacterial cultures of tracheal wash were statistically evaluated. The percentage of neutrophils in the BAL was correlated with several fitness parameters, negatively affecting aerobic capacity; analogously, horses with neutrophilic or mixed MEA showed worse athletic capacity compared with those with eosinophilic–mastocytic MEA. These results suggest that lower airway neutrophilia negatively affects sports performance. ABSTRACT: Mild–moderate equine asthma (MEA) is a common respiratory disorder among racehorses, characterized by lower airway inflammation. Although it is generally agreed that MEA causes poor performance, contrasting results have been reported about the effects of tracheal mucus and the leukocyte populations of the bronchoalveolar lavage (BAL) on performance. This study aims to investigate the associations between airway inflammation and fitness parameters measured during an incremental treadmill test on Standardbred racehorses. For this purpose, the clinical records of 116 Standardbreds subjected to a diagnostic protocol for poor performance were retrospectively reviewed. Parametric and nonparametric statistics were used to evaluate the relationships between endoscopic scores, BAL cytological results, and fitness parameters. Moreover, horses were divided into MEA and non-MEA groups and into neutrophilic, eosinophilic–mastocytic, and mixed MEA groups; fitness parameters were compared between groups. Neutrophils percentages were inversely correlated with the speed at a heart rate of 200 bpm, the speed and heart rate at a plasma lactate concentration of 4 mmol/L (VLa4 and HRLa4), and the maximal speed, while they were positively correlated with higher lactate concentrations. Moreover, significant differences were detected between different MEA subtypes concerning VLa4, HRLa4, and lactate concentrations. These results suggest that airway neutrophilic inflammation impairs athletic capacity in Standardbreds.