Effect of Season on Oocytes and in Vitro Fertilization by Fresh and Frozen Semen of Cattle

The aim of the research is to study the effect of season on the quality of bovine oocytes and semen (fresh and frozen) used for in-vitro maturation and fertilization. Fresh ovaries were collected from slaughtered animals by aspiration with 18- gauge needle attached to a 5 ml syringe filled with (flushing fluid). The oocytes were classified to Grades A and B after washing 3 times by the fluid, the oocytes were left in the incubator for 18-22 h to mature at 38°C and CO 2 5%. After 18-22 h, the cumulus cells were removed and washed 1-2 times to remove all the cumulus cells around the oocytes. The matured oocytes and the capacitated sperms (fresh and frozen) were incubated in the fertilizing medium and checked daily for seven days. The results showed that the aspiration technique significantly (p < 0.01) gave a high percent of good quality oocytes with homogenous cytoplasm in comparison to fair and denuded oocytes. Moreover, the maturation (the first polar body appeared) also was significantly increased during summer, autumn and winter compared to spring (p <0.05). The rate of embryo morula stage increased significantly (p < 0.05) with using the fresh semen compared to frozen ones (54.52% vs. 38.02 %). In conclusion, season and fresh semen play an important role in the rate of success of in-vitro fertilization in cattle.