Effect of lung inflammation on lactate threshold in standardbred racehorses with moderate equine asthma

Moderate Equine Asthma (MEA) is a common disease of young racehorses characterized by coughing, mucus accumulation and inflammation of the airways and diagnosed by cytological examination of bronchoalveolar lavage fluid (BALF). Despite the large evidence concerning the role of MEA as a cause of poor performance, it is difficult to quantify the impact of lung inflammation on the racing fitness. The most common parameter for equine athletic performance is the speed at 4 mmol/L of lactate (VLA4). Aim of the present work was to evaluate the effect of the different BALF inflammatory cells on VLA4 in racehorses affected by MEA. Data from a cohort of 258 Standardbred racehorses in training investigated for poor performance were retrospectively evaluated. All horses underwent an accurate diagnostic protocol, which included an incremental treadmill test, with plasma lactate analysis and calculation of VLA4, and BALF collection. Horses with any other alteration potentially influencing performance were excluded, considering only those subjects with BALF cytology consistent with MEA. Of the 258, a sample of 30 horses (average age 3.4±1.0 y.o., median age 3.5 y.o.) was selected. The association between BALF inflammatory cells differential count and VLA4 was evaluated by means of linear regression. Statistical analysis showed a significant association (p=0.015, r2 0.19) between the increase in neutrophils differential count in BALF and the decrease in VLA4. The results obtained suggest that neutrophils accumulation in the airways of MEA horses may have a direct impact on athletic capacity, possibly due to impaired alveolar-blood gas exchanges during strenuous exercise, confirming the role of neutrophilic MEA as a cause of poor performance in Standardbred racehorses.