Initiation of Reproductive Function and Subsequent Activity of the Corpora Lutea in Prepuberal Gilts2

Abstract

A series of three experiments were conducted to study the mechanisms involved in the maintenance of pregnancy in prepuberal gilts which had been induced to ovulate with injections of PMSG and followed with either HCG or an LH releasing factor. In the first experiment ova were recovered 4 days after administration of HCG to gilts 155 to 185 days old. Rates of recovery of ova were 51% to 79% and rates of ova cleavage were 52% to 69%, except in gilts 175 days old. There was both a low recovery and cleavage rate for ova from those gilts. The number of gilts pregnant at 25 days of gestation for those 155, 165, 175 and 185 days old were respectively: 1/10, 2/10, 2/10 and 5/10, with average litter sizes of four to five fetuses. The number of gilts farrowing increased from one of five in those 155 days old to four of five in those 185 days old with average litter sizes of 1.0 to 5.5 pigs. In the second experiment priming dosages of progesterone and estrogen administered prior to the induction of ovulation had no effect on fertility 25 days into the gestation period. Those same steroids administered after the induction of ovulation increased the number of gilts pregnant at 25 days of gestation from two of 10 to five of 10 and five of nine. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science.