Successive ovum pick-up followed by in vitro embryo production (OPU-IVP) during pregnant periods in Japanese black cattle

This study was aimed to examine the effect of successive ovum pick-up followed by in vitro embryo production (OPU-IVP) during pregnant or nonpregnant periods in Japanese Black cattle on the efficiency of premature oocyte collection and IVP and on serum sex hormone levels of the donor. OPU was performed at various time points, either during the post parturition nonpregnant period or 9 to 61 days after artificial insemination (AI), in thirteen parous cows, including four that were repeatedly used. These donors were divided into pregnant (seven cows) and nonpregnant (four cows that hednot received AI and two that had not conceived after AI). When the efficiency of OPU was compared between the pregnant and nonpregnant groups, the average number of collected oocytes was 9.8 (recovery rate 76.7%) and 16.8 (84.8%), and the proportions of grade A-C oocytes was 72.3 and 62.7%, respectively. In pregnant cows, although the number of aspirated follicles, the number of collected oocytes and the rate of collection were significantly lower (p0.05, p0.01 and p0.05, respectively), the percentage of grade A-C oocytes was significantly higher (p0.05). The rate of IVP embryos developing into the 5-cell stage or later and the blastocyst stage were, respectively, 43.4 and 16.2% for the pregnant donors and 53.2 and 11.1% for the nonpregnant. The serum estradiol (E2) levels of some pregnant cows showed small peaks at 3 and 10 days after the second OPU, and cows in two-month or earlier pregnancy showed cyclic follicular development. The serum progesterone (P4) level of pregnant cows stayed around 2 ng/ml regardless of OPU timing. In the nonpregnant group, on the other hand, serum E2 was generally at high levels, considerably ranging from 1 pg/ml to the estrus 8 pg/ml level. The E2 level tended to increase especially at the second OPU and 10 days after that, suggesting new follicular growth synchronous to OPU. The P4 level in nonpregnant cows remained low around 1 ng/ml throughout the experimental period. Of nine cows that received consecutive OPU post-AI, seven cows were conceived, thus resulting in a favorable conception rate of 77.8%. A11 pregnant cows went into labor, although two newborns died of dystocia caused by fetal oversize and abnormal posture. In conclusion, our results show that in vitro production of OPU embryos derived from pregnant cows facilitates efficient reproduction of high genetic merit donors without affecting the conception rate or delivery interval.