Physiological and glucocorticoid response to treadmill exercise of Holstein heifers

Effect of exercise for 8 wk prepartum on heart rate, respiration rate, rectal temperature, and serum glucocorticoid concentration was determined for nine Holstein heifers. Exercise was on a treadmill 30 min daily, 5 d/wk, for approximately 8 wk. Physiological measures were taken at rest and immediately postexercise; blood samples were taken via jugular vein cannulas at 2-h intervals 26 h preexercise, at 10-min intervals during exercise and 21.5 h postexercise, all at initiation of the experiment and again near the end of pregnancy. The three physiological measures increased during exercise at both the initiation and termination of the 8-wk exercise period. Mean serum glucocorticoids of heifers increased from 5.4 to 21.3 ng/ml during initial exercise but increased from 4.4 to 5.2 ng/ml following approximately 8 wk exercise. These glucocorticoid data mimic trends found in other species, i.e., physically fit subjects or animals trained to chronic exercise have lower glucocorticoids than sedentary or untrained subjects during intense or exhaustive exercise.