Changes in the plasma LH, progesterone, and estradiol during the ovulatory cycle of the duck ( Anas platyrhynchos domestica) exposed to different photoperiods

Abstract

Luteinizing hormone (LH), progesterone, and estradiol concentrations in the plasma of Khaki Campbell female ducks under various photoperiods were determined by radioimmunoassays at 2-hr intervals during the ovulation cycle. Ducks maintained under 14L:10D (lights on at 5:00 and off at 19:00), 16L:8D (lights on at 6:00 and off at 22:00), and 18L:6D (lights on at 6:30 and off at 0:30) conditions laid eggs mostly during 3:30–5:30, 6:00–8:00, and 7:30–9:30, respectively. Delaying the time of lights off for 3 and 5.5 hr resulted in delaying the time of oviposition for about 2.5 and 3.5 hr, respectively. Plasma LH, progesterone, and estradiol started to increase shortly after the time of lights off in all the ducks which ovulated. The peaks of these three hormones were observed 3, 5, and 1 hr before ovulation in the ducks maintained under 14L:10D, 16L:8D, and 18L:6D conditions, respectively. A small peak of estradiol was observed 17 hr before ovulation. No peaks of LH, progesterone, and estradiol were observed in the plasma of ducks which failed to ovulate. These results strongly suggest that the onset of darkness is closely linked to the induction of plasma LH and progesterone increases and lights off may be the signal for the induction of ovulation in the female duck.