Hematological changes and athletic performance in horses in response to high altitude (3,800 m)

This study had two goals: 1) measure hematologic changes with high-altitude acclimatization in horses; and 2) assess the effect of 9 days at high alti tude on subsequent athletic performance at low altitude. Six horses perform ed standardized exercise tests on a dirt track (before and during time at a ltitude) and treadmill (pre- and postaltitude exposure). Resting and immedi ate postexercise blood samples were measured for blood volume, lactate, red cell number, packed cell volume, and 2,3-diphosphoglycerate (DPG) concentr ations at 225 m, over a 9-day period at 3,800 m, and shortly after returnin g to 225 m. Acclimatization produced increases in total red cell volume (38 .2 +/- 2.4 to 48.1 +/- 2.9 ml/kg, P = 0.004) and DPG/hemoglobin concentrati ons (19.4 +/- 1.7 increased to 29.4 +/- 0.4 mu mol/g, P = 0.004). Two perfo rmance variables, heart rate recovery postexercise and lactate recovery, we re faster after acclimatization.