Abstract: In this study, it was aimed to investigate the effect of different treatment durations of luteinizing hormone (LH) on maturation in vitro of bovine oocytes. The experiments were designed as following：first,the bovine cumulus oocytes complexes(COCs) were matured in vitro in medium with or without LH, the appropriate GVBD rate about it was recorded and analyzed to determine the time course of their maturation in vitro. Second,the bovine COCs were in vitro matured in medium with LH during different durations respectively (0 to 3 h,0 to 6 h,0 to 9 h and 0 to 24 h). After 24 h for in vitro maturation, their percentage of polar bodyⅠ(pbⅠ) was also analyzed. The GVBD rate in the group treated with LH for 6 h(30.19%±5.22％) was significantly lower than the control 1 group (48.42%±5.92%) (P＜0.05). Meanwhile, the percentage of polar bodyⅠ(pbⅠ) in group 4 treated by LH (81.05%±2.70％) was significantly higher than that of the control 2 group (65.89%±3.34％)(P＜0.05). Thus, it might be concluded that LH may improve the nuclear maturation of bovine oocytes while they are matured in vitro within 24 h.

Key words: luteinizing hormone (LH); bovine; oocytes; in vitro maturation