[Bovine 17-beta-estradiol during estrous cycle]

Using a highly specific antiserum, a method of plasma estradiol-17 beta determination by R.I.A. without chromatographic separation, was developed. Increasing on day 18, estradiol-17 beta reached a peak level of 8.6 pg/ml (6.4-12.6) at the onset of estrus. It then sharply decreased, and remained at a low level 1.75 pg/ml with secondary peaks on day 4-5, 12 and sometimes on day 8.