Airway endoscopy and tracheal cytology of two-year-old Thoroughbred horses during the first year of race training

Abstract

The immunological status of the respiratory tract is critical to racehorses’ performance. Respiratory diseases in young Thoroughbred (TB) racehorses are a major concern during their early athletic career. This study investigated the airway adaptations occurring in young TB race horses during their first year of race training. Eighteen animals were evaluated at five different time points over a one-year follow-up period. A physical examination was performed, followed by airway endoscopy, in which tracheal mucus (TM) and pharyngeal lymphoid hyperplasia (PLH) were observed. Differential cytology of the tracheal wash (TW) was also performed. The physical parameters in the five assessments and TM grade did not vary. The PLH grade was lower at time-points 3 (T3) and 4 (T4) than at the initial evaluation (T0) (P=0.028 and P=0.036, respectively). The cytological analysis revealed that neutrophil count decreased at T4 as compared with T0 (P=0.022). Epithelial cell count was increased, and macrophage count decreased, at T3 and T4, compared with T0 (P=0.004 and P=0.031, respectively). Haemosiderophage count was higher at T1 (P=0.020) and lower at T2 (P=0.003), compared to T0. A statistical correlation between mucus and all cell types was found, showing a non-specific immune response. In conclusion, young TB racehorses underwent airway modifications during the initial months of race training, and a thorough follow-up is needed during the initial period after stabling.