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

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 24 h in the presence or absence of E₂. Incubation in 1 μg/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 24 h of in vitro incubation. At 0 h, > 70% of oocytes already had undergone germinal vesicle breakdown. After 12 h, ∼70% of oocytes had reached metaphase I of nuclear maturation, with ∼75% achieving TI/MII by 24 h 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.