Najin, one of the world's last northern white rhinos, retires from breeding

Najin, a 32-year-old northern white rhino, has been retired from a breeding program aimed at saving the species after researchers found benign tumors on her reproductive organs. She is one of only two surviving northern white rhinos worldwide.

(CNN)Hopes that mankind can save the northern white rhino from extinction appeared more remote than ever this week, after scientists announced they will retire one of the last two living northern white rhinos from a breeding program.

Najin, a 32-year-old northern white rhino -- who, along with her daughter Fatu is one of only two left in the world -- will no longer be harvested for eggs for "ethical" reasons, the team of researchers from the BioRescue consortium announced in a press release Thursday.
Rhinos are targeted by poachers, fueled by the belief in Asia that their horns cure various ailments. As a result, the northern white rhino subspecies is on the brink of extinction.
    Najin, who was born at a safari park in Czech Republic in 1989, was moved to the Ol Pejeta Conservancy in Kenya in 2009 as part of a breeding program to revive the population.
      Fatu, pictured here in July at the  Ol Pejeta Conservancy, is now the last white rhino in the breeding program.
      She was moved there with her daughter, Fatu, along with the world's last two male northern white rhinos -- who died in 2014 and 2018.
        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.
        However, neither Najin nor Fatu have been able to carry a pregnancy to full term.
          The researchers, 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 -- her daughter, Fatu, who is more than a decade her junior.