New approaches to detect cortisol administration in the horse.

The cortisol threshold concentration of 1.0 microg/ml in horse urine adopted by the International Federation of the racing Authorities in 1994 is specific. However, an increase in the sensitivity for the detection of cortisol administration would be helpful. Previous studies have shown that 20beta-dihydrocortisol concentration in urine would be a good indicator of cortisol administration. The purpose of the present work was to estimate the population parameters and the critical values of 20beta-dihydrocortisol and 20beta-dihydrocortisone concentration in urine compared with that of cortisol. Using the same probability (1.1 x 10(-4)) which was used for the establishment of the official cortisol threshold, the critical values of 5000 ng/ml for 20beta-dihydrocortisol and 350 ng/ml for 20beta-dihydrocortisone were obtained. Considering these 2 critical values for 20beta-dihydrocortisol and 20beta-dihydrocortisone, the time during which a horse could be declared positive is significantly increased.