Embryos produced with serum show the alterations in their ultrastructure, impaired compaction, abnormal blastulation, aberrant mRNA expression profiles and large calf syndrome with greater incidences of stillbirths and deaths after birth. The aim of the present study was to describe in vitro embryo production by analyzing embryo production, fetal production and pregnancy rate in free-serum medium. The OPU-IVP data used in this study from 2016. Approximately, sixteen cows (Hanwoo), which belonged to the Institute of Gyeongsang National University, were used. Two experimental group is used in this study. Serum groups were conducted in March to July and free-serum group was conducted in September to December. The recovered cumulus-oocyte complexes were morphologically classified to four grades based on the compaction of cumulus cells layers and homogeneity of the cytoplasm. The number of oocyte was significantly greater in serum groups than that in free-serum groups (29.61 ± 0.63 vs. 15.6 ± 0.62; p < 0.05). Between serum and free-serum groups indicate that average of 1st and 2nd grade oocytes were no difference (2.38 ± 1.67 vs. 2.38 ± 1.48; p > 0.05), but number of 3rd and 4th grade oocytes were greater in serum groups than that in free-serum groups (7.31 ± 7.64 vs. 5.60 ± 6.29; p < 0.05). Embryo cleaved competence was higher in rate in free-serum groups than that in serum groups (62.1% vs. 58.3; p < 0.05). However, blastocyst developmental rate was no difference between serum and free-serum groups (33.1% vs. 43.5%; p < 0.05). 986 recipients were used for embryo transfer. Pregnancy rate was indicated that between serum and free-serum group was no difference (54.6% vs. 56.3%; p < 0.05). In conclusion, we developed the free-serum system for production of in vitro bovine embryos in order to meet the developmental and qualitative requirements for large scale commercial use.

ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSION
CONFLICTS OF INTEREST
ACKNOWLEDGEMENTS
AUTHOR’S AFFILIATION, POSITION ANDORCID NO.
REFERENCES

• Byung-Hyun Choi(Division of Applied Life Science (BK21 Plus), Gyeongsang National University, Jinju 52828, Korea, GAST, Gyeongsang National University, Jinju 52828, Korea)
• Bun-Young Park(GAST, Gyeongsang National University, Jinju 52828, Korea)
• Rami Kong(Division of Applied Life Science (BK21 Plus), Gyeongsang National University, Jinju 52828, Korea, GAST, Gyeongsang National University, Jinju 52828, Korea)
• Mi-Ju Son(GAST, Gyeongsang National University, Jinju 52828, Korea)
• Chan-Sang Park(Division of Applied Life Science (BK21 Plus), Gyeongsang National University, Jinju 52828, Korea, GAST, Gyeongsang National University, Jinju 52828, Korea)
• Nyeon-Hak Shin(Gyeongnam-do Provincial Government Livestock Research Institute, Sancheong 52263, Korea)
• Hye-Young Cheon(Gyeongnam-do Provincial Government Livestock Research Institute, Sancheong 52263, Korea)
• Yeong-Rok Yang(Gyeongnam-do Provincial Government Livestock Research Institute, Sancheong 52263, Korea)
• Jin-Woo Lee(Gyeongnam-do Provincial Government Livestock Research Institute, Sancheong 52263, Korea)
• Jong-In Jin(Institute of Agriculture and Life Science, Gyeongsang National University, Jinju 52828, Korea, GAST, Gyeongsang National University, Jinju 52828, Korea)
• Il-Keun Kong(Division of Applied Life Science (BK21 Plus), Gyeongsang National University, Jinju 52828, Korea, Institute of Agriculture and Life Science, Gyeongsang National University, Jinju 52828, Korea) Corresponding author