Maternal Recognition of Pregnancy in the Rabbit: Effect of Conceptus Removal1

Abstract

The time at which maternal recognition of pregnancy occurs in the rabbit has not been established. To determine the time in gestation when the conceptuses become essential for maintaining corpus luteum function, conceptuses were removed by either flushing the uterus on Days 5 and 6 postcoitum (pc) or by extrusion through incisions in the uterus on Days 10, 14, 18, and 26 pc. Pseudopregnant does were similarly treated on Days 5, 6, 10, and 18 pc. Progesterone profiles were utilized to monitor corpus luteum function. Serum progesterone profiles of does whose conceptuses were removed during the preimplantation period, on Days 5 and 6, or during the early postimplantation period, Day 10 pc, were identical to those of both intact and sham-operated pseudopregnant rabbits. However, conceptus removal on Days 14, 18, or 26 pc resulted in a significant decrease in progesterone levels within 48 h after surgery. These data clearly demonstrate that maternal recognition of pregnancy occurs some time between Days 10 and 18 pc and that the conceptuses provide a continuous, or at least an episodic, signal to maintain continued corpus luteum progesterone secretion.