Up-to-date artificial insemination (AI) using frozen sperm consider as the most widely using technology for improvement of Korean Native Cow (Hanwoo) embryo production. However, it is time consuming, required at least 15~20 years to make more than 6 generations, and their offspring number is limited. To overcome such limitations, superovulation and in vitro fertilization have been developed. For superovulation, the number of produced embryos are not enough for commercialization and donor cows need rest period. This led to use of slaughterhouse ovary for in vitro fertilization, but it is impossible to repeat the collection from the same individual and it only can improve the genetic merits of offspring for one generation. Production of embryos using Ovum Pick-Up (OPU) technique, where oocytes can be repeatedly collected from living elite donor, might overcome these limitations. In this study, we investigated the possibility of using OPU technique from donors at different age and different session periods for mass-embryo-production. Oocytes were collected from 26 donor cows twice per week, 3 - 4 months per year, between 2013 and 2016. Results showed that, the average number of embryo produced in first year used donor was significantly higher than that in second year used donor (3.89 ± 2.85 vs 3.29 ± 2.70), however, there was no significant difference between third year used donor (3.51 ± 3.32) and other groups. Taken together, our data showed that repeated using of donor up to three years is possible for in vitro embryo mass-production. Moreover, OPU can be used as suitable embryo producing technique for livestock breed improvement.

Abstract
 INTRODUCTION
 MATERIALS AND METHODS
  1. Chemicals
  2. Ethics statement
  3. Experimental design
  4. Recovery of oocytes by OPU technique
  5. Oocyte collection and in vitro maturation (IVM)
  6. In vitro fertilization (IVF) and IVC
  7. Statistical analyses
 RESULTS
  1. Follicle and oocyte dynamics for session
  2. Embryo development rate and the number of blastocysts
 DISCUSSION
 REFERENCES

• Byung-Hyun Choi(Division of Applied Life Science (BK21 Plus), GAST, Gyeongsang National University)
• Seok-Hwan Song(Division of Applied Life Science (BK21 Plus))
• Bun-Young Park(GAST, Gyeongsang National University)
• Rami Kong(Division of Applied Life Science (BK21 Plus), GAST, Gyeongsang National University)
• Mi-Ju Son(GAST, Gyeongsang National University)
• Chan-Sang park(Division of Applied Life Science (BK21 Plus), GAST, Gyeongsang National University)
• Nyeon-Hak Shin(Gyeongsangnamdo Livestock Experiment Station)
• Hye-Young Cheon(Gyeongsangnamdo Livestock Experiment Station)
• Sung-Hoon Lee(Gyeongsangnamdo Livestock Experiment Station)
• Jong-In Jin(Institute of Agriculture and Life Science, GAST, Gyeongsang National University)
• Jung-Gyu Lee(Institute of Agriculture and Life Science, GAST, Gyeongsang National University)
• Il-Keun Kong(Division of Applied Life Science (BK21 Plus), Institute of Agriculture and Life Science) Correspondence