They believe that in successfully transferring a rhinoceros embryo for the first time, they are a step closer to being able to reproduce the critically endangered creature.
Reviving the northern white would help to “heal the ecosystem” in central and eastern Africa, according to conservationists.
The last two northern white rhinos left in the world, both females, live at the Ol Pejeta Conservancy in Kenya, under 24-hour guard from poachers, but are unable to carry pregnancies.
So the scientists implanted an embryo created in a laboratory into a surrogate mother, a southern white rhino, which is a different but related species.
The next step will be to repeat the procedure using northern white embryos. The work is thought to be the last chance to save the northern white, whose dwindling numbers due to poaching have been watched helplessly by conservationists for years.
Since 2020, conservationists have created 30 embryos of the species, by using eggs from Fatu, the younger female in Kenya, and sperm taken for artificial insemination from two male northern whites before they died.
The embryos are stored in liquid nitrogen in Germany and Italy.
In the latest procedure, the scientists transferred a southern white rhino embryo to find out whether the procedure could work.
The successful impregnation of a southern white rhino with an embryo of the same species was a milestone, project leader Thomas Hildebrandt said.
“We achieved something that was not believed to be possible,” he said.
The trial suffered a setback when the bull and surrogate mother, along with the foetus, were killed by an infection which the team said was caused by bacteria following a mudslide.
The foetus was only 70 days old – but the experts said they were confident it could have survived the pregnancy.
Later this year, the scientists, led by the Leibniz Institute for Zoo and Wildlife Research, plan to implant other surrogates with northern white rhino embryos.
The Ol Pejeta Conservancy was also home to Sudan, the last male northern white rhino, who died in 2018.
“This animal played a crucial role in a complex ecosystem before it got extinct for a while. It lived in the landscape and architecture of central Africa, and bringing back the northern white rhino to this ecosystem will help to heal the ecosystem,” Mr Hildebrandt told The Washington Post.