This study was performed to investigate the result that in-vivo or in-vitro embryos of Hanwoo cows were transferred to Holstein cows. Seventeen Hanwoo cows were used as donors for production of in-vivo embryos and fresh hanwoo in-vivo embryos were transferred to 1,150 Holsteins. And 2 embryos were transferred to 188 Holstein recipients to produce twin calves. Diagnosis on pregnancy was performed by rectal palpation at $60sim90$ days after transfer. The pregnancy rate of Holstein recipients was 55.8% after transfer with Hanwoo in-vivo embryos and 38.2% after transfer with Hanwoo in-vitro embryos. The delivery rate of pregnant Holstein recipients was 88.4% after transfer with Hanwoo in-vivo embryos and 75.6% after transfer with Hanwoo in-vitro embryos. The rate of delivery of Holstein recipients transferred with two Hanwoo embryos was 36.2% and the rate of twin production was 25.9%. The rate of twin production by embryo transfer with in-vivo embryos was 30.4%, whereas the fate with in-vitro embryos was 15.6%. The pregnancy rate according to the grade of corpus luteum of Holstein recipients transferred with Hanwoo in-vitro embryos was 41.5 and 36.0% for A and B grade, respectively. The pregnancy rate according to the transfer in site in the uterine lumen of recipients was 40.9 and 32.7% for anterior and middle site, respectively. The pregnancy rate according to day of embryo transfer after estrus of recipients was 45.5, 38.8 and 39.7% for day 6, day 7 and day 8, respectively. There was difference of pregnancy rate according embryo transfer technician ($30.5sim45.8%$) individual dairy farm ($21.1sim51.0%$). These results are supposed to indicate that the rate of pregnancy after transfer with Hanwoo embryos to Holstein recipients was similar to that within the same breed, and consequently that this method would be beneficial to enhance the productivity in Hanwoo reproduction.

Keywords: Hanwoo, embryo transfer, pregnancy rate, in-vivo, in-vitro