Scientists at the University of Connecticut (UConn) announced Monday that they and their Japanese colleagues have produced six genetically identical calves using cells cultured for up to 3 months.

Four calves were born in December 1998 from cells cultured for two months and two more cloned calves were born in February 1999 from three months culture.

The cells were taken from the ear of a 17-year-old prize bull which is the father of about 160,000 offspring under artificial propagation.

A paper on the technology appears in the January 4 issue of the US Journal "Proceedings of the National Academy of Sciences".

In the rapidly evolving field of cloning technology, it has been believed that long-term culture of donor cells would compromise their efficiency for cloning.

But the UConn scientists say that long-term culture of donor cells may do just the opposite and may make it possible to manipulate genetic modifications in the donor cells prior to cloning.

Their findings could have enormous implications in the cattle industry and in the future applications of cloning technology in biomedical research.

Dr. Xiangzhong (Jerry) Yang, head of the UConn Transgenic Animal Facility and corresponding author of the article, says the significance of this research should set the stage for future targeted gene manipulations of the donor cells. (Xinhua)