The Relationship between Lung Inflammation and Aerobic Threshold in Standardbred Racehorses with Mild-Moderate Equine Asthma

SIMPLE SUMMARY: Horses can be affected by equine asthma, a disease that shares several similarities with human asthma. Young racehorses can be affected by a mild form of equine asthma, which can have a negative impact on racing performance. In this study, we evaluated the relation between the increase in inflammatory cells in the bronchoalveolar lavage fluid of horses affected by poor performance due to equine asthma and the speed at which the horse blood lactate reaches the value of 4 mmol/L, which is a parameter of athletic capacity. With this aim, we evaluated the results of a treadmill test with blood lactate analysis of 30 horses that had a bronchoalveolar lavage fluid cytology consistent with a mild form of equine asthma. The results showed a significant relation between the increase in the differential count of neutrophils in bronchoalveolar lavage and the decrease in the speed at 4 mmol/L of lactate. This confirm the negative impact of neutrophilic lung inflammation in the presence of equine asthma on athletic capacity and, consequently, on racing performance. ABSTRACT: Mild–moderate equine asthma (MEA) is a common disease of young racehorses characterized by inflammation of the lower airways diagnosed by cytological examination of bronchoalveolar lavage fluid (BALF), and it is considered an important cause of poor performance. The most common parameter of athletic capacity associated with horse performance is the speed at 4 mmol/L of lactate (VLA4). The aim of the present work was to evaluate the relation between the different BALF inflammatory cells and VLA4 in racehorses affected by MEA. A population of Standardbred racehorses that underwent an accurate protocol for poor performance evaluation was collected for a retrospective study. Horses with any other alteration potentially influencing performance were excluded, thus considering only subjects with BALF cytology consistent with MEA. A sample of 30 horses (3.4 ± 1.0 years old) was selected. The relationship between BALF inflammatory cell differential count and VLA4 was evaluated by means of linear regression. Statistical analysis showed a significant relation (p = 0.015, r(2) = 0.19) between the increase in the differential count of neutrophils in BALF and the decrease in VLA4. The results obtained suggested that the accumulation of neutrophils 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.