Free Swimming and Exercise-Induced Pulmonary Hemorrhage in Endurance Horses: A Preliminary Study.

Swimming is used for rehabilitation of musculoskeletal injuries and for conditioning to improve equine fitness. However, there are anecdotal reports that suggest that tethered swimming can induce epistaxis, likely secondary to exercise-induced pulmonary hemorrhage (EIPH). The objective of this observational, prospective study was to investigate if EIPH occurs during intensive free-swimming training sessions (5 × 70m) using 15 endurance horses. On tracheo-bronchoscopic evaluations following swimming, low grade mucus scores were observed, but no tracheal blood was observed. Bronchoalveolar lavage fluid analysis revealed a low cellularity, and the median red blood cell count (RBCs) was 271 cells/μL (interquartile range 150-363 cells/μL), which is much lower than the threshold of RBCs >1,000 cells/μL for horses to be considered positive for EIPH. Therefore, free swimming does not seem to predispose endurance horses to EIPH following a typical free-swimming training session.