On Oct. 8, 1998, a team from Kinki University reported the first successful cloning of adult cows. To date, five groups had produced a total of 19 calves cloned from adults as part of an ongoing government campaign to improve the quality of beef cattle.

The researchers used cells taken from the oviducts and cumulus, the tissue that surrounds the oocytes, or egg cells, of a single adult cow. The scientists starved the cells into quiescence, then transferred their DNA-carrying nuclei into egg cells stripped of their own nuclei. After reactivating the cells with an electric shock, the group grew several oocytes in culture to the blastocyst stage. They then selected 10 blastocysts and implanted them in five hosts. All became pregnant.

Their study findings appeared in the journal Science.