Plasma Concentrations of Six Steroids and LH During the Ovulatory Cycle of the Hen, Gallus domesticus1

Five laying hens were serially sampled via a brachial vein cannula at 2 h intervals for a period of 34 to 72 h. Plasma samples were grouped to the nearest 2 h interval relative to the estimated time of ovulation, and subsequently each sample was assayed for progesterone (P4), estradiol-17β (E2), estrone (E1), testosterone (T), 5α-dihydrotestosterone (DHT), corticosterone (B), and LH. Mean concentrations of plasma LH, P4, E1, E2, and DHT were highest 6 h prior to ovulation, while a peak of T preceded ovulation by 8 h. There was a surge of B preceding ovulation by 2 h; however, this is attributed to a peak related to oviposition and not to ovulation. There was a small daily surge of LH occurring at the onset of darkness regardless of whether an ovulation occurred on the subsequent morning. These hormone fluctuations are discussed with reference to the potential direct or indirect role of each hormone in the induction of ovulation.