Abstract: Objective To improve superovulation and establish a method of embryo freezing for rats. Methods Different doses of PMSG-HCG (15 IU，20 IU，25 IU/rat) were injected (i.p.) into three groups(Group A，B，C) of 5 weeks SD rats, and each treated female was coupled with fertile male, the effect of each dose was compared to determine the best dose for superovulation. Two-cell was collected by clysising fimbriae tubae. The embryos were divided into 2 groups. Embryos in group 1 were frozen for 1 minute, and embryos in group 2 for 5 minutes. All the embryos of rats were frozen according to the standard method for mouse embryos frozen. The embryos were resuscitated, and the rate of resuscitation were compared to assess the two method. Results The average number of zygotes obtained from each rat in group A，B，C was 13 土 12.7，31 土 14.2，and 41 土 25.4. There were significant differences among the groups (P＜0.05). The resuscitation rate of embryos in group 1 is 88.3%, and 84.9% in group 2. Of 152 rat embryos were frozen for 1 minute, 139 embryos were successfully resuscitated, and cultured for 20 minutes.The normal cultured 105 embryos were transplanted into pseudopregnant rats, and 39 offspring were obtained. Conclusion The method for rat superovulation has been successfully improved, and a method of embryo freezing for rats has been established.

Key words: Rat, Superovulation, Embryo freezing