136 IMPACT OF SELECTION SYSTEM BY KINETICS ON THE EARLY EMBRYONIC DEVELOPMENT IN BOVINE OVUM PICKUP-IVF EMBRYOS

Abstract

Recently, in vitro-produced (IVP) embryos have been increasingly produced using ovum pickup (OPU) and IVF in cows worldwide. However, the conception rate of IVP embryos is lower than that of in vivo-derived embryos. This study was conducted to determine the proportion of embryos that led to a high conception rate when the embryos were selected according to the 4 predicting factors. A total of 30 Holstein and 20 Japanese Black cows were used, and 81 OPU-IVF sessions were performed from October 2014 to May 2016. The collected cumulus-oocyte complexes (COC) were cultured for 22 h. Capacitated sperm (at a final concentration of 5 × 10⁶ spermatozoa/mL) were incubated with COC for 6 h. After insemination, presumptive zygotes were separated from cumulus cells and sperm by pipetting. Then, the presumptive zygotes were cultured for 9 days in CR1aa supplemented with 5% calf serum by using a micro-well culture dish (Dai Nippon Printing, Tokyo, Japan). The kinetics of embryo development was observed at 27, 31, and 55 h post-insemination (hpi). The 4 factors used to select embryos were as follows: (1) time at which first cleavage occurred (less than 27 hpi, or less than 31 hpi, in case any of the zygotes did not cleave at 27 hpi in each culture dish); (2) 2 blastomeres after first cleavage at 31 hpi; (3) absence of fragments after first cleavage at 31 hpi; and (4) 8 or more blastomeres at 55 hpi. The number of blastocysts was analysed at 7, 8, and 9 days post IVF. Additionally, the number of produced embryos that could be used for embryo transfer (ET) was determined. The data were analysed using the chi-square test. The total numbers of blastocysts and produced embryos were 615 and 503, respectively. The numbers of blastocysts and produced embryos selected using the combination of factors 1 to 4 were 200 (32.5%) and 169 (27.5%), respectively. The numbers of blastocysts and produced embryos selected using factor 1 were 397 (64.6%) and 340 (67.6%), using factor 2 were 445 (71.3%) and 378 (75.1%), using factor 3 were 364 (81.8%) and 307 (81.2%), and using factor 4 were 374 (60.8%) and 308 (61.2%), respectively. The numbers of blastocysts and produced embryos that were rejected using a combination of factors 1 to 4 were 123 (27.5%) and 90 (17.9%), respectively. The conception rate of fresh embryo transfer was 46.6% (n = 73). We found that the conception rate of the embryos selected using factors 1 to 4 was significantly (P < 0.05) higher than that of embryos without one factor or more [60.0% (n = 35) v. 29.4% (n = 34)]. These results show the applicability and efficiency of the 4 factors for producing embryos with a high competence for conception.