Studies Of The Effects Of Vc On Bovine Pre-implantation Embryo Development And The Factors Affecting SCNT Cloned-Cattle

In vitro maturation（IVM）of bovine oocytes and production efficiency of cloned cattle by somaticcell nuclear transfer (SCNT) are affected by many factors. In order to obtain bovine oocytes in highquality and improve the productivity of SCNT cloned-cattle The roles of different concentrations ofvitamin C (Vc) and the effects of factors like number of transferred embryos, seasonal changes andphysiological conditions of surrogate cattle on the production of SCNT cloned-cattle were investigatedin this study.The results showed that:(1) The IVM medium containing50μg/ml of VCimproved thematuration rate of bovine oocytes significantly, while no significant effects on the development ofparthenogenetic embryos was observed; The in vitro culture (IVC) medium containing20μg/ml VCsignificantly increased the cleavage rate of in vitro fertilized(IVF) embryos, remarkably enhanced themRNA levels of pluripotency-related genes in blastocysts, while had no significant effect on the rate ofblastocyst formation. Respective supplements of50μg/ml and20μg/ml Vc into IVM and IVCmedium increased the cleavage rate of IVF embryos significantly and improved the mRNA expressionlevels of pluripotency genes in the blastocysts greatly; Different concentrations of VCcould affect theexpression of apoptosis-related gene of the embryos, but their anti-apoptosis effect was not significant.(2) Compared with one-or three-embryo transfer, two-embryo transfer resulted in relatively higherpregnancy rate, lower abortion rate and higher calving rate; The efficiency of embryo transfer in spring,summer and autumn (from May to September) was significantly better than that of winter (fromDecember to January); The pregnancy rate of surrogate cattle with corpus luteum of A and B rank issignificantly higher than that with C rank; The results indicate that number of transferred embryos,seasonal changes and physiological conditions of surrogate cattle have a critical impact on theproductivity of cloned-cattle by SCNT. In this study, techniques of bovine oocyte IVM and proceduresof SCNT cloned-cattle were optimized, which will provide a theoretical and experimental basis forfurther improving the quality of bovine IVM oocytes and the productivity of SCNT cloned-cattleproduction program.