PHYSIOLOGICAL-CHANGES DURING MAXIMAL TREADMILL EXERCISE OF POORLY PERFORMING STANDARD-BRED HORSES WITH OR WITHOUT TRACHEAL BLOOD POSTEXERCISE

From a group of 46 young racing Standardbreds presented for problems o f decreased athletic performance, eight with complete physiologic data were found to have blood in the trachea (POS) within one hour post-ma ximal exercise test on a high speed treadmill. This group was compared to those horses from the larger group of 46 which had no tracheal blo od post-treadmill exercise (NEG). Parameters measured during the tread mill test included maximal speed (V-max), heart rate (HR(max), respira tory and stride frequency (RF, SF respectively) at maximal speed, aero bic capacity (VO2 max/peak), and post-exercise plasma lactate concentr ation (Lac). Within one hour of the exercise, bronchoscopy and broncho alveolar lavage were also performed. Of the physiologic parameters mea sured there were no differences between the groups in V-max, HR(max), SF, VO2 max/peak, or Lac, but there was a significant decrease in RF a t end exercise (85+/-5.9 versus 96+/-10.9 breaths per minute, p<0.05) in the POS group of horses. The bronchoalveolar findings were suggesti ve of increased airway inflammation in more of the POS horses, whereas all horses had hemosiderophages present. This study suggests that som e horses with post-exercise blood in the trachea may have an associate d decrease in respiratory rate at the point of fatigue during exercise . However, it also brings into question the validity of using tracheal blood as the sole criterion for sanctioned, yet empirical treatment o f race horses for exercise-induced pulmonary haemorrhage.