This is an intermediate stage technique that will be used until it becomes possible to grow new replacement ovaries:

Collecting ovary tissue from rare animals and growing eggs in other species "could help preserve genetic diversity within endangered species," says one of the researchers, Shae-Lee Cox of Monash University in Clayton,Victoria. It could also speed up livestock breeding, help the study of egg development in exotic species, and even preserve fertility in cancer patients.

Cox and her colleagues grafted sections of mouse ovaries onto rat kidneys. The rats had their immune systems suppressed and so did not reject the tissue. The scientists collected eggs from the ovaries, fertilized them and then implanted the resulting embryos into a surrogate mouse.

Five healthy pups were born from 31 different transplants. All five mice were fertile and went on to produce their own healthy pups.