Effects of Zinc Supplementation During In Vitro Maturation on Meiotic Maturation of Oocytes and Developmental Capacity in Yak

Zinc (Zn) is an essential trace element that is required during mammalian developmental processes. The objective of this study was to investigate the effects of Zn supplementation during in vitro maturation (IVM) on the developmental capacity of yak (Bos grunniens) oocytes. Cumulus expansion, nuclear maturation, intracellular glutathione (GSH), reactive oxygen species (ROS) levels, superoxide dismutase (SOD) activity, subsequent embryonic development, and the expression of Zn transporters (ZnTs) and Zrt and Irt-like proteins (ZiPs) were evaluated. The Zn concentrations in yak plasma and follicular fluid were 0.740 ± 0.012 and 0.382 ± 0.009 μg/mL, respectively. The cumulus expansion did not show significant differences in COCs after matured with or without Zn supplementation (P > 0.05). The intracellular GSH was higher in oocytes matured with 1 or 2 mg/L Zn than in control group (0 mg/L) (P < 0.05). However, ROS levels of oocytes matured with 1 or 2 mg/L Zn were reduced significantly compared with the control and 0.5 mg/L groups (P < 0.05). The SOD activity was increased significantly after Zn supplementation. The cleavage rate was not significantly different after Zn supplementation (P > 0.05). Percentages of matured oocytes that developed into the blastocyst stage after IVF were 47.9, 50.5, 60.4, and 58.9% for 0, 0.5, 1, and 2 mg/L Zn groups, respectively. Gene expression analysis revealed that the expression patterns associated with Zn were changed after Zn supplementation. In conclusion, Zn supplementation to IVM improved yak oocyte maturation and subsequent development by increasing GSH and SOD activity, decreasing ROS in oocytes.