Oocyte quality and estradiol supplementation affect in vitro maturation success in the white-tailed deer (Odocoileus virginianus)

Abstract: White-tailed deer oocyte biology is not well documented. The objective of this study was to determine (1) the influence of estradiol (E2) supplementation on meiotic resumption and the ability to “rescue” poorer quality (lower grade) oocytes and (2) the kinetics of oocyte nuclear maturation in vitro in the white-tailed deer. In Experiment 1, immature oocytes harvested during hunting-culling operations were cultured for 24h in the presence or absence of E2. Incubation in 1μg/mL E2 promoted nuclear maturation (to telophase I, TI; or to metaphase II, MII) in a higher proportion of Grade 1 oocytes (∼77%; P<0.05) compared with that in Grade 2 or Grade 3 counterparts (∼51%). For Grades 2 and 3 oocytes, there was no advantage (P>0.05) for E2 supplementation in reaching TI/MII. In Experiment 2, Grade 1 oocytes were cultured in the presence of E2 and nuclear status evaluated at 0, 3, 6, 12, and 24h of in vitro incubation. At 0h,>70% of oocytes already had undergone germinal vesicle breakdown. After 12h, ∼70% of oocytes had reached metaphase I of nuclear maturation, with ∼75% achieving TI/MII by 24h in vitro. In summary, adding E2 to an in vitro maturation (IVM) culture system for white-tailed deer was advantageous, but only for the highest quality oocytes, with ∼75% achieving nuclear maturation. In contrast, E2 supplement did not benefit lower-grade oocytes, half of which will reach MII, with the other half failing. Under the described culture conditions, good-quality white-tailed deer oocytes achieve nuclear maturation over a time duration comparable with that reported in other ungulates. [Copyright &y& Elsevier]