Supplementation of progesterone on establishment of pregnancy, resynchronization of estrus, and development of in vitro-produced bovine embryos

Progesterone is necessary for the maintenance of pregnancy and has been associated with embryonic mortality. Five experiments were conducted to discover the role of progesterone on establishment of pregnancy, resynchronization of estrus, and development of in vitro produced bovine embryos. The objective of experiment 1 was to determine whether an ovulatory estrus could be resynchronized in previously synchronized artificially inseminated (AI) nonpregnant cows without compromising pregnancy from the previous synchronized ovulation or to those inseminated at the resynchronized estrus. Treatments consisted of a vaginal insert containing progesterone administered after a timed AI (TAI) at different timepoints, and for differing durations. It was determined that pregnancy rates to the initial TAI were similar and the resynchronization of estrus was successful in two treatments, however, fertility in those treatments was decreased. In experiment 2, we established the concentrations of progesterone in the lumen of the uterine horn and oviduct to establish a base concentration to be used in further experiments. Using uterine flushes of estrus synchronized heifers and fluid collection of reproductive tracts post-slaughter; we determined that, while concentration of progesterone was highly variable in females, the mean was nearly 1 ng/mL. The objectives of experiments 3 and 4 were to determine the effects of culturing in vitro produced embryos with or without a co-culture of bovine oviductal epithelial cells (BOEC) with or without two concentrations of progesterone on embryo development. We determined that co-culture of bovine embryos with BOEC decreased development and the addition of progesterone decreased development of embryos. The objective of experiment 5 was to determine if the addition of two concentrations of progesterone at two stages of culture impacted embryo development, embryo metabolism and numbers of cells in each embryo. We determined that while some characteristics changed slightly with the addition of progesterone, overall viability was not increased or decreased dramatically. Our conclusion was that although we do not fully understand the role of progesterone on embryonic mortality, we were unable to affect pregnancy rate or embryonic development with the concentrations and timing of progesterone employed in these experiments.