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Initiation of Reproductive Function and Subsequent Activity of the Corpora Lutea in Prepuberal Gilts^{1, 2,}

North Carolina State University, Raleigh 27607 and Duke University, Durham, North Carolina 27710

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.

¹ Paper No. 4574 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh. Contribution from the Reproductive Physiology Research Laboratory, Department of Animal Science. Research supported in part by Special Grant Project No. 916-15-32 from the Cooperative State Research Service, U.S.D.A. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Experiment Station of the products named, nor criticism of similar ones not mentioned.

² The authors are grateful to Dr. Jeanne Martin for carrying out the solid phase synthesis of LRF under this study. The PMSG used in the third experiment was supplied by the National Institute of Arthritis and Metabolic Diseases Rat Pituitary Hormone Program.

³ Supported by a graduate research assistantship from the North Carolina Pork Producers. Present address: Department of Animal Science, University of Georgia, Athens.

⁴ Present address: Colby, Kansas.