Physiologic changes during maximal treadmill exercise of poorly performing Standardbred horses with or without tracheal blood post-exercise

Abstract

From a group of 46 young racing Standardbreds presented for problems of decreased athletic performance, eight with complete physiologic data were found to have blood in the trachea (POS) within one hour post-maximal exercise test on a high speed treadmill. This group was compared to those horses from the larger group of 46 which had no tracheal blood post-treadmill exercise (NEG). Parameters measured during the treadmill test included maximal speed (Vmax), heart rate (HRmax), respiratory and stride frequency (RF, SF respectively) at maximal speed, aerobic capacity (VO2 max/peak), and post-exercise plasma lactate concentration (Lac). Within one hour of the exercise, bronchoscopy and bronchoalveolar lavage were also performed. Of the physiologic parameters measured there were no differences between the groups in Vmax, HRmax, SF, VO2 max/peak, or Lac, but there was a significant decrease in RF at 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 suggestive of increased airway inflammation in more of the POS horses, whereas all horses had hemosiderophages present. This study suggests that some horses with post-exercise blood in the trachea may have an associated 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 of race horses for exercise-induced pulmonary haemorrhage.