New insights into the function of progesterone in early pregnancy

Abstract

• Successful growth and development of the post-hatching blastocyst and pregnancy establishment are a result of the interaction between a competent embryo and a receptive uterine environment. • Progesterone (P4) plays a key role in reproductive events associated with establishment and maintenance of pregnancy through its action on the uterine endometrium. • Low concentrations of circulating P4 after ovulation have been associated with a reduction in conceptus growth and elongation, a decrease in interferon-tau production, and reduced pregnancy rates in cattle. • Elevated concentrations of circulating P4 in the immediate postconception period have been associated with an advancement of conceptus elongation, an increase in interferon-tau production and, in some cases, increased pregnancy rates in cattle. • Administration of P4 early in the oestrous cycle of the recipient can effectively advance uterine receptivity for the transfer of older asynchronous embryos. • Despite the potential beneficial effects of exogenous P4 supplementation on fertility, results of supplementation studies have been inconsistent and may be related to the strategy used to achieve high P4, the type of animal (e.g., lactating or not) as well as endogenous concentrations in the animal.