Replacement of fetal calf serum with synthetic serum substitute in the in vitro maturation medium: Effects on maturation, fertilization and subsequent development of cattle oocytes in vitro

Abstract

The aim of this study was to investigate the possibility of using synthetic serum substitute (SSS) instead of fetal calf serum (FCS) in maturation medium to stimulate in vitro maturation (IVM). fertilization (IVF) and subsequent development of bovine oocytes. Ovaries were obtained from a local slaughterhouse. Selected oocytes were matured in tissue culture medium 199 (M-199) supplemented with 2 mM glutamine + 0.25 mM Na-pyruvate + 0.5 mug/ml of FSH + 5 mug/ml of LH + 25 mug/ml of gentamycin and 10% FCS or 10% SSS (FCS and SSS groups, respectively) for 22 h. Matured oocytes were fertilized in vitro using frozen bull sperm. Fertilization day was taken as day 0 in the present study. Forty-eight h after IVF, the numbers of 2-4-cell stage embryos were recorded and they were transferred into CR1aa culture medium for in vitro culture until day 8. In addition, blastocyst numbers were recorded on day 8. A total of 255 and 250 oocytes were used for the FCS and SSS groups, respectively. The cleavage rate of the FCS group (73.7%; 188/255) was significantly higher (P < 0.001) than that of the SSS group (30.0%; 75/250). While the blastocyst formation rate of the FCS group was 16.1% (41/255), no blastocyst development was observed in the SSS group. The difference between the groups in terms of blastocyst formation was also significant (P < 0.001). These results show that serum supplementation of the IVM medium is necessary to obtain a higher cleavage rate and development rate to the blastocyst stage of immature bovine oocytes recovered from ovaries obtained from slaughterhouses. In conclusion, further studies are required to replace FCS with SSS in the maturation medium, and supplementation with growth factors might improve cleavage and development rates in maturation medium supplemented with SSS.