The hormone profile in the blood plasma of heifers after cycle synchronization with prostaglandin F2alpha

Highly sensitive radio-immuno assay (RIA) was used for 21 days to study the curves of several steroid hormones, progesterone (P), oestradiol 17 beta (E2), and testosterone (T), as well as of luteinizing hormone (LH) in peripheral blood of six heifers to which oestrus had been induced by prostaglandin F2 alpha. The validity of the authors' RIA for P, E2, and T determination in blood plasma was positively verified by two reliability criteria, correctness and accuracy, as well as by comparative determinations, using reference methods. Only four of the six heifers returned to oestrus, within 21 days from first oestrus induction. A typical cycle-related curve of the P concentration in peripheral blood with peak values between the 13th and 17th days of cycle (15-26 nmol/l) was recorded from four animals. The peak values of pre-ovulatory E2 and LH were between 33.0 and 53.2 pmol/l or between 19.5 and 52.5 micrograms/l. Some of the T rises in peripheral blood were in parallel to E2 concentrations. All hormone curves are presented in detail and are discussed in relation to clinico-physiological findings.