135 Effect of Different Bovine Breeds on Efficiency of Embryo Production by Ovum Pick-Up-IVF

Abstract

Production of bovine embryos by ovum pick-up (OPU)-IVF has increased in recent years. However, numerous factors affect efficiencies of embryo production using this technology. This study was investigated the effects of different breeds on embryo production by OPU-IVF. In total, 98 OPU-IVF sessions were conducted on 41 Holstein and 27 Japanese Black cows from February 2015 to May 2017. The collected cumulus–oocyte complexes (COC) were matured for 22 h. After co-culture of COC with sperm for 6 h, the presumptive zygotes were washed and denuded by pipetting. Those zygotes were then cultured in CR1aa medium supplemented with 5% calf serum for 9 days in a micro-well culture dish. Blastocyst formation rates were analysed at 9 days post-insemination (hpi). The kinetics of embryo development was observed at 27, 31, and 55 hpi. Four factors were considered for selecting embryos to predict pregnancy competence: (1) timing of first cleavage; (2) formation of 2 blastomeres after first cleavage at 31 hpi; (3) absence of fragments after first cleavage at 31 hpi; (4) formation of 8 or more blastomeres at 55 hpi. The quality of blastocysts was compared with the proportions of embryos that were selected based on these 4 factors. Data were analysed by the Chi-squared test with Yates’ correction and Student’s t-test. Total numbers of COC from Holstein or Japanese Black cows were 1330 (n = 51) and 1543 (n = 47), respectively. However, no differences were observed in the numbers of collected and cultured COC per OPU session between Holstein (26.1 ± 20.1 and 21.7 ± 20.1) and Japanese Black (32.8 ± 24.7 and 28.7 ± 22.7) cows. The percentage of COC linked into Grade 1, 2, or 3 was 47.6, 32.1, and 10.7% for Japanese Black and 45.8, 25.6, and 12.2% for Holstein cows, respectively. The proportion of COC with expanded cumulus cells was significantly higher (P < 0.01) in Holstein (12.7%) than in Japanese Black (7.7%) cows. The number of blastocyst and transferable embryo production per OPU session in Holstein (7.5 ± 8.3 and 7.3 ± 7.7) cows was not different from that in Japanese Black (10.6 ± 9.3 and 9.8 ± 9.0) cows. Moreover, there was no difference in blastocyst formation rates between Japanese Black (36.8%) and Holstein (34.8%) cows. Percentages of embryos selected by factors 1 to 4 were 42.6, 66.8, 59.1, and 54.4% in Holstein, and 54.6, 83.2, 72.2, and 75.2% in Japanese Black cows, respectively. Proportions of blastocysts in Holstein and Japanese Black cows selected by a combination of all 4 factors were 21.6 and 36.1%, respectively. There were significant differences (P < 0.01) between the 2 breeds in terms of proportion of blastocysts selected based on individual factors as well as a combination of all 4 factors. These results suggested that the efficiency of embryo production did not differ between Japanese Black and Holstein cows. However, the quality of embryos selected by a combination of 4 factors was significantly higher in Japanese Black than in Holstein cows.