After the males died the breeding program continued with sperm harvested from the males. The scientists then harvest the females’ eggs before fertilizing them in a laboratory.
しかしながら, neither Najin nor Fatu have been able to carry a pregnancy to full term.
研究者, led by the Leibniz Institute for Zoo and Wildlife Research in Germany, said in the press release that they had made the “exceptionally difficult” decision having undertaken an “in-depth ethical risk assessment.”
“Oocyte [ovary cell] collections in Najin have yielded only few eggs and none of them could be fertilized successfully to become an embryo.
“Weighing this outcome with potential risks, it is the most responsible decision to cease any further intervention on Najin and to stop using her as a donor of oocytes,” they said in the press release.
“She will remain a part of the program, for example by providing tissue samples for stem cell approaches, which can be performed with minimal invasion.
The researchers added that they had found multiple small, benign tumors on her reproductive organs.
The retirement of Najin from oocyte collections leaves just one living northern white rhino left in the breeding program — 彼女の娘, Fatu, who is more than a decade her junior.