Retention and development of eggs transferred to the uterus at various times after ovulation in the rabbit

The pattern of egg expulsion/retention was determined in rabbits 24 h after transfer of eggs to the uterus 24-84 h p.c. Nearly all eggs transferred at 24 or 36 h p.c. were expelled into the vagina but from 36 h onwards an increasing proportion was retained in utero, although maximum retention was not recorded until 76-84 h p.c. In rabbits in which both uterine horns were ligated before egg transfer at 12-48 h p.c., egg development was evaluated 24 or 72 h later, or at term. Practically all eggs transferred at 12 or 24 h perished within 3 days; however, from transfers at 36 h 25% of eggs implanted with 40% survival to term, and further improvement in endometrial receptivity occurred by 48 h. These findings reveal a clear time difference between limitations imposed by endometrial and myometrial function on egg development. Limited attempts to create more favourable uterine conditions by means of progesterone treatment were unsuccessful.