Effect of 5 different types of exercise, transportation and ACTH administration on plasma cortisol concentration in sports horses.

This study was carried out to compare the changes in plasma cortisol concentration produced by 5 different types of exercise, transportation and ACTH administration. Venous blood was analysed for cortisol concentration before and after each stimulus. The types of exercise were show jumping (n=28), cross country phase of a three-day event (n=32), trot race (n=9), gallop race (n = 10) and endurance ride (n=8). The response following the intravenous injection of synthetic ACTH (200 µg) in 6 of the event horses was determined. The ACTH test was carried out one week after competition. In 5 horses, the response to road transport of one hour was studied. All stimuli, except transportation produced a significant increase in plasma cortisol concentration. The endurance ride produced the largest increase and the show jumping the smallest. ACTH administration resulted in a 164% rire in plasma cortisol. Il was concluded that I) the degree of increase in plasma cortisol concentration appeared to reflect both intensity and dotation of workload; endurance ride appeared to be the most exhaustive and show jumping the least; 2) there was a correlation (r2=0.82) between the individual cortisol response to cross country exercise and to exogenous ACTH in the saure horses and 3) there was an important individual effect on transport-induced cortisol changes.