title: Suckling-induced delay of implantation and increased fecundity in rats.
abstract: In rats fertilized during the 1st or 2nd day postpartum (second consecutive pregnancy), suckling induces intrauterine blastocyst dormancy and delays implantation for 8-22 days. In spite of this relatively long time of blastocyst dormancy, associated with greatly reduced cellular metabolism, subsequent implantation and growth results in significantly larger litters (13.6 +/- 0.62; means +/- SE) than in primigravidas (10.4 +/- 0.89) or in rats with a second-spaced pregnancy (11.2 +/- 0.72). Enhanced fecundity in rats with second consecutive pregnancies may be attributed to increased ovarian blood supply of preceding gestation and/or to augmented pituitary FSH-LH secretion resulting in intensified ovarian gonadotropic stimulation for postpartum ovulation.
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000502:physiology*; D010064:Embryo Implantation; D005260:Female; D005298:Fertility; D007774:Lactation; D008098:Litter Size; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains