Plasma oestrogen, progesterone and other reproductive responses of gilts to photoperiods.

Abstract

Yorkshire gilts in 18 cool-white fluorescent light with 6 h dark daily and those in 9.0-10.8 h natural light exhibited puberty earlier (165 and 175 days: P less than 0.05) and had more corpora lutea (13.5 and 12.6: P less than 0.05) than those reared in complete darkness (200 days and 11.3 respectively). Weekly samples of plasma showed significant fluctuations of progesterone which confirmed the different times of the first over oestrus (puberty). In all 3 groups total oestrogen concentrations showed a peak at about 135 days. The correlation between oestrogen and progesterone values changed from a positive to a negative value at about 135 days of age. It is suggested that the oestrogen peak marks a time of change in sensitivity of the reproductive system to hormonal feedback.