Effect of oocyte selection, estradiol and antioxidant treatment on in vitro maturation of oocytes collected from prepubertal Boer goats

Development of improved procedures for in vitro maturation of oocytes collected from prepubertal goats has applications for in vitro embryo production and accompanying strategies for genetic improvement. The objective of described studies was to determine the effects of oocyte grade, in vitro maturation time, antioxidant supplementation and concentrations of estradiol in the maturation medium on in vitro maturation of oocytes harvested from 1- 6 mm follicles present on the ovaries (obtained from an abattoir) of 1-6-month old prepubertal Boer goats. Rates of progression to metaphase II were greater for Grade 1 oocytes (>3 compact layers of cumulus cells and evenly granulated cytoplasm) than Grade 2 oocytes (<3 layers cumulus cells and evenly granulated cytoplasm) and were lowest for Grade 3 oocytes (devoid of cumulus cells with abnormal cytoplasm). No significant effects of maturation for 24 vs 27 vs 30 h on progression of oocytes to metaphase II were observed. The addition of 5 ìM â-mercaptoethanol to maturation medium increased the proportion of oocytes progressing to metaphase II and glutathione content in such oocytes, whereas supplementation with 10 mM hypotaurine was without effect. A significant inhibitory effect of in vitro maturation in the presence of high concentrations of estradiol (10 and 100 ìg/mL) on progression to metaphase II was observed, and no effect was observed in response to 1 ìg/mL estradiol treatment as compared with control. Results suggest that oocyte selection and â-mercaptoethanol supplementation can positively influence progression to metaphase II of oocytes harvested from ovaries of prepubertal goats, whereas high concentrations of estradiol are inhibitory to in vitro maturation.