BEIJING, Aug. 15 (Xinhuanet) -- Researchers have come up with a way of extracting sperm from frozen mice in such a way that it yields normal, healthy offspring, according to a paper published in Tuesday's issue of the U.S. journal Proceedings of the National Academy of Sciences.

Sperm is often frozen for use in assisted reproduction for humans and other animals, as well as for conserving endangered species. However, defrosted sperm is not always capable of fertilizing an egg.

But the researchers from Japan, Britain and the United States have found that sperm can be frozen safely for much longer than previously thought, so long as they are kept in organs or whole carcasses and cooled slowly to minus 20 degrees Celsius or lower.

Using sperm from whole mice and testes that had been frozen for between one week and 15 years, they were able to fertilize eggs and obtain healthy offspring.

"If spermatozoa of extinct mammalian species can be retrieved from animal bodies that were kept frozen for millions of years in permafrost, live animals might be restored by injecting them into (eggs) from females of closely related species," the researchers wrote.

The research was led by Atsuo Ogura from the Institute of Physical and Chemical Research in Ibaraki, Japan, and funded by the Japanese ministries of education and health, and the Human Science Foundation of Japan. Enditem

(Agencies)