Researchers will stop harvesting eggs from one of the two remaining northern white rhinoceros in the world, according to a Thursday announcement by BioRescue, according to the AFP.

Efforts to bring the species back from the brink of extinction are still underway. Currently, BioRescue is focusing on extracting eggs from the two remaining northern white rhino females. However, the scientific consortium announced on Thursday that one of the females, 32-year-old Najin, will be retired as a donor from the project.

Although Najin has been a valuable participant, and despite all the care being taken during its various procedures, BioRescue simply feels like the risks to Najin outweigh the benefits she could bring to the program at this point.

Hard choice to make

“Weighing up risks and opportunities for the individuals and the entire species rendered this decision without an alternative,” BioRescue said in a statement.

The only other northern white rhino on Earth, and Najin’s daughter, Fatu, has thus remained the sole egg donor for the program. Using her cells, researchers will try to develop viable embryos. Neither Fatu nor Najin are able to carry a pregnancy to term, so surrogate mothers from the closely-related southern white rhino subspecies will be used.

This assisted reproduction programme has been underway since 2019.

Harvesting of the eggs involved a high-risk procedure. Although it was carried out by an international team of excellent veterinarians, it still required the animals to be anesthetized for almost two hours, and the extraction process involved the use of specialized techniques — all of which means that there was an unavoidable level of risk involved in the programme.

Thankfully, the process was successful. The eggs were then taken to a lab in Italy for fertilization, development into embryos, and preservation. Frozen sperm from two (now-deceased) male northern white rhinos was used for this step.

So far, the programme has resulted in the creation of three embryos of the northern white rhino subspecies. But these were all developed from eggs harvested from Fatu. As such, it simply doesn’t make sense to keep risking Najin’s wellbeing.

“She will remain a part of the programme, for example by providing tissue samples for stem cell approaches, which can be performed with minimal invasion,” said Jan Stejskal, director of international projects at Safari Park Dvur Kralovs, where Najin was born in 1989.

It’s safe to say that programmes such as this one are the subspecies’ last shot at avoiding extinction. Sudan, the last male northern white rhino, died at the Ol Pejeta Conservancy in Kenya in 2018. Najin and Fatu are currently living under permanent guard at the same location.

Those guards are not meant to protect the animals from predators. Rhinos only need to fear precious little threats in the wild. Their populations were decimated, instead, by poachers over the last 5 decades or so.