Calves Derived from in Vivo Frozen-Thawed Embryos Collected from Canada Holstein Friesian Cows with High Genetic Background

Embryo Transfer (ET) is one of the assisted reproductive technologies and a useful tool for improving herds. The purpose of this study is to produce the calves using frozen embryos which were produced in the top one percent Holstein in Canada by ET. One hundred seventeen recipients were used for surrogate mothers and seventy cows were diagnosed to be pregnant. Fifty seven calves were born successfully and thirteen out of them failed to produce viable calves (abortion: 4, stillbirth: 9). Their gestational length, birth body weight and sex ratio for all the viable calves (n = 57) were 278.1 ± 3.6 days (range: from 271 to 286 days), 44.0 ± 3.0 ㎏ (range: from 37 to 49 ㎏) and 57.9 vs. 42.1 % (male 33 and female 24), respectively. Microsatellite analysis confirmed that they were derived from frozen embryos. In conclusion, this study demonstrated that viable calves derived from frozen-thawed embryos from Canada were born by ET.