138 Effects of different treatments of donors on the efficiency of embryo production and conception in bovine ovum pickup-in vitro production

Abstract

An in vitro-produced bovine embryo has a low conception rate compared with that of an in vivo embryo. The present study was conducted to examine the effects of different treatments delivered to donors before ovum pickup (OPU) sessions to improve the conception rate of in vitro-produced bovine embryos. In total, 351 OPU sessions were performed on 138 Holstein and 213 Japanese Black cows from January to December 2017. Donors were divided into 4 groups based on their pretreatment before OPU: (1) single injection of 2.5 AU of FSH 40 h before OPU; (2) CIDR insertion on Day 0, injection of 2 mg of oestradiol benzoate on Day 1, 4 injections of FSH (each 2.5 AU) every 12 h beginning from Day 5 to 7, followed by removal of CIDR and OPU on Day 9; (3) injection of 50 μg of gonadotropin-releasing hormone 72 h before OPU; or (4) no pretreatment. The collected cumulus-oocyte complexes were matured for 22 h in 25 mM of HEPES buffered TCM-199 supplemented with 5% newborn calf serum and 0.02 AU mL⁻¹ FSH. After 6 h of gamete co-culture (5.0 × 10⁶ sperm mL⁻¹), the presumptive zygotes were washed and the remaining cumulus cells were denuded by pipetting. The presumptive zygotes were then cultured in KSOMaa supplemented with 5% newborn calf serum for 9 days in a micro-well culture dish (Dai Nippon Printing, Tokyo, Japan). Blastocyst formation rates were analysed 9 days after insemination, and the formed blastocysts were transferred to oestrous synchronized recipients on the seventh or eighth day after oestrus. The data were analysed by Chi-squared test with Yates correction. The average numbers of collected oocytes were 57.7 ± 17.4 (n = 136), 25.3 ± 12.8 (n = 20), 28.8 ± 12.5 (n = 18) and 24.3 ± 12.9 (n = 177) in groups 1 to 4, respectively. Groups 1 and 2 showed significantly (P < 0.01) high percentages of Grade-1 oocytes (52.1 and 49.6%, respectively) compared with groups 3 and 4 (37.3 and 39.9%, respectively). The proportion of blastocysts in groups 1 (38.6%) was significantly different compared with that in groups 2 (32.1%) and 4 (35.3%), but the difference was insignificant in the case of group 3 (36.4%). The conception rates in groups 1 (43.5%, n = 868) and 2 (59.1%, n = 44) were significantly (P < 0.05) higher than those in groups 3 (35.1%, n = 57) and 4 (34.9%, n = 768). These results suggest that although the efficiency of embryo production did not differ largely between donors pretreated with 4 FSH injections and those without any pretreatment, the conception rate in donors pretreated with 4 FSH injections was significantly higher than that in donors without pretreatment. Moreover, donors pretreated with a single injection of FSH showed significantly high efficiency of embryo production and conception rate than donors without pretreatment.