The Effects of Progesterone on Oviposition and Ovulation in the Domestic Fowl (Gallus Domesticus)

1. Following an injection of 0.5 or 0.1 mg progesterone/kg between 0 and 6 h after ovulation, oviposition of the resulting egg was delayed by 1 to 11 h and occurred 26 to 31 h after injection, depending on the dose. The injection terminated the laying of a sequence of eggs by causing the next ovulation to occur a day late. The delayed ovulation occurred at the time normally expected for the first ovulation a sequence and became the first of a new sequence. 2. Following an injection of 0.5 or 0.1 mg progesterone/kg between 6 and 15 h after ovulation, oviposition of the resulting egg was generally delayed by between 15 and 28 h and occurred at the same time of day as the next ovulation, which was delayed as in the first experimental situation. Subsequent ovulations were resynchronised and followed at intervals according to the normal sequence established before the injection. 3. Injection of 0.5, 0.1 or 0.05 mg progesterone/kg between 12 and 9 h before expected ovulation advanced the oviposition of the egg already in the uterus (shell gland) by about 3 h. The succeeding ovulation was either advanced or blocked. 4. These observations suggest that the pre-ovulatory surge of progesterone is directly or indirectly involved in the timing of oviposition and ovulation.