Scientists have successfully impregnated a rhino using embryo transfer for the first time, marking a significant breakthrough in conservation efforts to save the world's population of the northern white rhinoceros.

Only two northern white rhinos are left on Earth: a mother named Najin, 33 years old, and her daughter Fatu, age 23. Both live in Kenya at Ol Pejeta Conservancy, where they are closely guarded.

The vast majority of the population of the endangered animal was killed by poachers, who reduced the population from around 500 to 15 in the 1970s and 1980s.

At a press conference in Berlin on Wednesday, researchers for the German government-funded Biorescue project announced they had successfully impregnated a southern white rhinoceros named Curra in September 2023, using egg cells and sperm collected from donor rhinos.

This is significant because it confirms, for the first time, that embryo transfer can work in rhinos. Experts have said the procedure is crucial for saving the world's white rhino population from extinction..

Researchers have 30 preserved northern white rhino embryos stored in Italy and Germany and are awaiting transfer into southern white rhino surrogate mothers.

Pregnancy not carried to term

The sad news, however, is that Curra did not live to deliver a baby rhino.

After a 70-day pregnancy, Curra died in November after extreme flooding set dormant bacteria spores free at Kenya's Ol Pejeta Conservancy, where Curra was under close observation. A toxicology report showed that she died of an infection caused by the spores.

However, the Biorescue researchers said the success of the pregnancy is a good sign that the transfer technique could work in other northern white rhinos.

The northern white rhino and southern white rhino have compatible reproductive systems, the researchers said, which makes surrogacy possible.

Cesare Galli, director of Avantea, a lab in Italy where the embryos were created, said that although Curra's pregnancy had a long way to go, the "chances [had been] very high" — around 70% — that it would have been successful had she lived.

Susanne Holtze, a postdoctoral researcher at the Leibniz Institute for Zoo and Wildlife Research who is involved in the project, stressed this breakthrough had involved a "long and bumpy, sometimes windy road."

Curra's pregnancy came after two failed implantations and one ectopic pregnancy, which is when a fertilized egg grows outside of the uterus. It had taken five years of work to get from embryo to fetus.

However, Holtze told DW she was confident that impregnation of a southern white rhino with a northern white rhino embryo would be easier than Curra's impregnation with a southern white rhino embryo. She said the outer walls of the southern white rhino oocyte, a basic cell that becomes an egg, are thicker than those of the northern white rhino.

Embryo transfer as soon as June

Researchers said they may manage to transfer a northern white rhino embryo into a southern white rhino surrogate as soon as June 2024.

Northern white rhino pregnancies last 16 months. Once the northern white rhino is born, the researchers said, it will be crucial to integrate it with Fatu and Nijan so it understands itself and behaves as a typical northern white rhino.

To create a lasting population of northern white rhinos, researchers cannot use only the 30 embryos they have stored, as all 30 of the eggs are from Fatu. To create the genetic diversity needed to sustain a population, researchers said they were planning to use  gene editing.

If all goes well, in a few years the scientists involved in the project may be able to save the rhinos from "disappearing from the face of the Earth," said Samuel Mutisya, head of conservation at the Ol Pejeta Conservancy, at a press conference.

Hosting the last-known-to-exist white rhinos is a "huge responsibility," he said.

Edited by: Zulfikar Abbany