Effects of developmental regulation of follicles by estradiol-benzoate injection on the results of ovum pick up and in vitro fertilization techniques in cows

In order to improve the results of ovum pick up and in vitro fertilization(OPU-IVF) techniques by inducing growth phase follicles before oocyte collection, the effects of estradiol benzoate (EB) injection on follicular development, oocyte quality and embryo production were investigated in this study. Four cows (Japanese black cattle) were used, and each animal had OPU three times at seven days interval in one session. In the first session, OPU was done without any treatment (control). In the next session, from the result of pre-examination, each animal was injected with 1mg EB (ova hormone,Teikokuzouki Medical, Japan) intramuscularly six days prior to OPU, to set the timing of follicular development three to four days before the collection. Numbers of follicles, which were monitored daily by ultrasonography, and changes in plasma levels of estradiol-17beta (E2beta) were examined in both sessions. We also evaluated the numbers of the collected oocytes, morphological quality and the development rate to blastocysts after IVF. An acute rise in plasma E2beta was observed the day after EB injection, and high levels (10pg/ml) lasted for two days, while follicular development was suppressed. Plasma E2beta diclined to the basal level by the fourth day, in accordance with the beginning of follicular development. On the other hand, in the control session, follicular development began the day after OPU, and the numbers of follicles increased progressively. Although total numbers of follicles at OPU were slightly lower in the EB session (19.3 +- 6.1 vs. 22.7 +- 6.0, LS means +- SD), collecting rates of oocyte and AB ranked oocyte were higher in EB session than the control. Numbers of collected oocyte and AB ranked oocyte were similar in both session (10.9 +- 6.1 vs. 9.7 +- 7.2; 7.5 +- 3.5 vs. 6.6 +- 4.6, respectively). The development rate of blastocysts were significantly higher in the EB session (66.4 +- 1 8.1% vs. 40.9 +- 27.7%; P0.01), and the numbers of blastocysts tended to increase (5.3 +- 3.3 vs. 3.0 +- 3.1). In conclusion, the present study showed that EB injection is effective procedure for OPU, which can improve embryo production by inducing the numbers of growth phase follicles by the time of oocyte collection.