Regulation of Implantation and Establishment of Pregnancy in Mammals

Pat Lonergan, Niamh Forde, Lonergan, Pat, Forde, Niamh

Progesterone (P4) secretion by the corpus luteum is critical for the establishment and maintenance of pregnancy and plays a major role in regulating endometrial secretions essential for stimulating and mediating changes in conceptus growth and differentiation throughout early pregnancy. Numerous studies have demonstrated an association between elevated P4 and acceleration in conceptus elongation. Given that larger conceptuses produce more interferon tau, the pregnancy recognition signal in ruminants, it would be reasonable to hypothesize that treatments aimed at increasing peripheral concentrations of P4 should improve pregnancy rate. However, data on the impact of post-insemination supplementation of P4 on pregnancy rates are conflicting and, at best, indicate a modest positive response. Whether a P4-induced increase in conceptus size can improve fertility continues to be an active area of investigation. The aim of this chapter is to review recent data on the role of P4 in conceptus development in ruminants, particularly cattle, and to summarize results from attempts at manipulating endogenous P4 with the aim of improving conceptus survival and pregnancy rate.