Oviposition-Inducing Activity in the Ovarian Follicles of Different Sizes in the Laying Hen

The walls of the preovulatory follicles and the ruptured follicles collected during the middle of a clutch sequence were extracted separately for an oviposition-inducing factor. The activity of this factor in the follicular extracts was estimated by single intravenous injection of the extracts to hens with a soft-shelled egg in the uterus. Administration of the extracts from either follicles destined to ovulate in 20 to 27 hours or follicles in 46 to 53 hours failed to induce premature oviposition of soft-shelled egg in any of the hens treated. In contrast, the largest follicle within 1 hour prior to the expected ovulation exhibited a high activity for inducing premature ovipositions. This level of the activity seemed to be persisted in the subsequent ruptured follicle for several hours, followed by considerable decrease in activity after about one day or more days.