Efficiency of the production of bovine trophoblastic vesicles from elongating blastocysts derived from transfer of in-vitro-produced blastocysts or superovulation-artificial insemination

Co-transfer of bovine embryos with trophoblastic vesicles (TVs) is a useful method to improve pregnancy rate. However, efficiency of TVs production by recovering the elongating blastocysts derived from superovulation varies depending on the condition of donor cows such as response to hormone treatment. In the present study, we examined the efficacy of TVs production derived from elongating blastocysts which were produced by transfer of in vitro-produced blastocysts (ET) or superovulation-artificial insemination (SOV-Al). On day 14, ET-derived elongating blastocysts were recovered 7 days after transfer of 5-10 and 11-20 blastocysts. On day 17, ET-derived elongating blastocysts were recovered 10 days after transfer of 10 blastocysts. SOV-Al-derived elongating blastocysts were recovered 14 and 17 days after artificial insemination. TVs were generated from culture of trophoblastic fragments, which had been dissected from morphologically normal elongating blastocysts of longer than 3 mm in length. Numbers of recovered elongating blastocysts and TVs were compared among treatments. Numbers of total and intact elongating blastocysts embryos were significantly lower (P0.05) when elongating blastocysts were recovered on day 14 after transfer of 5-10 blastocysts (2.3 and 0.9) than those from ET of 11-20 (5.7 and 2.3) embryos or SOV-Al (8.3 and 2.7). On day 17, total and intact elongating blastocysts embryos were not different between ET (4.2 and 3.2) and SOV-Al (9.9 and 3.4). The rate of TVs formation and number of TVs from dissected trophoblastic fragments were higher when TVs were produced from elongating blastocysts recovered on day 17 after ET (93.5% and 31.6) than other groups (60.8-88.6% and 2.1-20.1). These results indicate that TVs production can be improved and widened more in a field by the method of embryo transfer of in vitro-produced blastocysts, which have developed to elongating blastocysts in vivo.