Sex ratio and conception rates of fresh/vitrified embryos at different developmental stages by ovum pick up in Hanwoo cows

Jihyun Park1, Seonggyu Bang1, Wonyou Lee2, Kilyoung Song3, Miyun Park3, Junseo Chung4, Islam Saadeldin1, Sanghoon Lee1, Junkoo Yi5,6,*, Jongki Cho1,**
Author Information & Copyright
1Chungnam National University, Daejeon 34140, Korea.
2Lartbio Ltd. 60 Haan-ro, Kwangmyeong-si, Gyeonggi-do 14322, Korea.
3ROAR Clinic, 550, Misa-daero, Hanam-si, Gyeonggi-do, Gyeonggi-do 12925, Korea.
4College of Veterinary Medicine, Chonnam National University, Gwangju 61186, Korea.
5School of Animal Life Convergence Science, Hankyong National University, Anseong 17579, Korea.
6Gyeonggi Regional Research Center, Hankyong National University, Anseong 17579, Korea.
*Corresponding Author: Junkoo Yi, School of Animal Life Convergence Science, Hankyong National University, Anseong 17579, Korea, Republic of. Gyeonggi Regional Research Center, Hankyong National University, Anseong 17579, Korea, Republic of. E-mail:
**Corresponding Author: Jongki Cho, Chungnam National University, Daejeon 34140, Korea, Republic of. E-mail:

© Copyright 2023 Korean Society of Animal Science and Technology. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


Embryo transfer plays a crucial role in enhancing the breeding value of livestock; it has been applied in Hanwoo cattle, which is a popular breed for beef production in Korea. Both <italic>in vivo</italic>-derived (IVD) and <italic>in vitro</italic>-produced (IVP) embryos are used for this purpose; however, IVP embryos have been preferred recently owing to advancements in ovum pick-up (OPU) technology and genomic selection. Despite technological advancements, comprehensive data on large-scale OPU/IVEP/embryo transfer in Hanwoo cows are lacking. In this study, 16 elite Hanwoo donor cows were selected on the basis of specific criteria. Oocytes were retrieved from 241 cows using OPU. The collected cumulus-oocyte complexes (COCs) were matured, fertilized, and cultured <italic>in vitro</italic> to produce transferable embryos. Embryos were classified according to their developmental stage and then transferred to 675 recipient cows. A total of 3,317 COCs were collected, with an average of 13.76 COCs per cow. The number of transferable embryos produced per cow was 3.7. Hanwoo OPU-derived IVP embryos exhibited a higher production yield than the global average, indicating a stable IVEP environment. Both fresh and frozen IVP embryos yielded similar conception rates; hence, the use of vitrified-thawed embryos in transfer plans feasible. However, frozen-thawed embryos at Stage 7 had a lower conception rate than those at earlier stages. There was no significant difference between the conception rates of sexually mature heifers and postpartum cows used as recipients. The male-to-female offspring ratio increased as the developmental stage progressed. Seasonal effects on conception rates were not observed; however, higher abortion rates and a higher proportion of male offspring were observed during winter. This study provides valuable data for improving the Korean embryo transfer industry, enabling more strategic growth of the domestic Hanwoo cow production.

Keywords: Embryo transfer; In vitro-produced (IVP) embryos; Ovum pick-up (OPU); Frozen-thawed embryos; Conception rate; Sex ratio