Progesterone enhances in vitro development of bovine embryos

Increased pregnancy rates in cattle given progesterone (P(4)) prior to 5 d after breeding have recently been reported. The objective was to determine if this increase in pregnancy rate could be attributed to a direct positive effect of P(4) on the developing embryo. In Experiment 1, 280 bovine oocytes were inseminated in vitro and at Day 3 (insemination = Day 0), good quality 8 cell embryos (n = 206) were randomly allocated to be cultured in either CR1aa+serum with 0 or similar to 15 ng/mL (n = 102 and n = 104, respectively). In Experiment 2, 881 bovine oocytes were used; on Day 3, good quality 8 cell embryos (n = 511) were randomly allocated to either the control (CR1aa+FCS, n = 168), vehicle (CR1aa + FCS + ethanol, n = 170), or P(4) treatment (CR1aa + FCS + similar to 15 ng/mL P(4) in ethanol, n = 173). On Day 7, in both experiments, there were increased numbers of blastocysts developing in the P(4) group (Experiment 1, 59% and Experiment 2, 71%) compared to the vehicle (Experiment 2, 53%) or control (40 and 62% in Experiments 1 and 2, respectively). The addition of P(4) (8%) stimulated the rate of embryo development (early blastocysts or more advanced stages on Day 6) compared to vehicle (3%) and control (0%) and the P(4) group had more hatched or hatching blastocysts (33%) on Day 9 compared to the control or vehicle group (21 or 22%). Additionally, the P(4) group had greater embryo diameter and significantly more Grade 1 blastocysts on Day 7. In conclusion, P(4) had a direct, positive effect on developing bovine embryos cultured in vitro. (C) 2012 Elsevier Inc. All rights reserved.