The fertility treatment used frozen sperm from three dead northern white bulls.
"An worldwide team of scientists has now successfully created hybrid embryos from Southern White Rhino (SWR) eggs and Northern White Rhino sperm using assisted reproduction techniques (ART)", the researchers from Avantea, a laboratory of advanced technologies for biotechnology research and animal reproduction, noted in a statement.
This could provide a way of "rescuing valuable genes" from a sub-species that is already functionally extinct; the last male northern white rhino, named Sudan, died earlier this year at the age of 45.
The two surviving members of the northern white species - a mother and daughter called Najin and Fatu - live in Kenya's Ol Pejeta Conservancy.
Researchers led by Dr Thomas Hildebrandt from the Leibniz Institute for Zoo and Wildlife Research have created hybrid rhinoceros embryos and derived stem cells from these using in vitro fertilisation, or IVF.
But the procedure is not without risk: "we have to do a full anaesthesia, the animal is down for two hours, and it is quite a risky situation" for the last two of their kind, conceded Hildebrandt. "We used ultrasound to very precisely inject a needle into [the area of the ovary that releases] eggs".
The team hopes that in the coming months, the Kenyan authorities will give permission for the collection of eggs of the two last females of the Northern white Rhino.
Early attempts were disappointing, but the results improved significantly when they zapped the eggs with two electrical pulses just after the sperm injection.
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Perhaps no species on Earth is closer to extinction as the northern white rhinoceros.
"Our results indicate that ART (assisted reproduction techniques) could be a viable strategy to rescue genes from the iconic, nearly extinct, northern white rhinoceros", the team wrote in the journal Nature Communications.
The short timeline is necessary, he said, so that a baby northern white rhino could be socialized by members of its own subspecies. These would then be implanted in southern surrogates, as the remaining northern females are unable to carry embryos themselves.
The last hopes were pinned on four white rhinos, two males and females living in zoos and nurseries in the United States, the Czech Republic and Africa. "Any embryos produced would likely need to be cryopreserved (or frozen) until a surrogate could be set up".
The breakthrough experiment was conducted with the primary goal of saving the northern white rhinos from extinction. Therefore, the best way of saving the rhinos from extinction is by stopping poaching but it has proven hard. Rhino horns even proved beneficial in the field of medicine.
Supporters believe the work could be used to help other endangered species, while some conservationists believe the focus should be on other critically endangered species, including the Javan and Sumatran rhinos, that have suffered because of poaching and human encroachment on habitats.
Furthermore, even if a few calves are born, "there will still be a lot of work to do in getting those offspring to propagate, and given the limited gene pool, inbreeding depression will be a very real threat", she said. Once this is accomplished successfully, it will be theoretically possible to selectively breed the hybrids to dilute the traits of SWR and concentrate those of the extinct species, giving birth to a pure population of northern white rhino.
He told the Independent: "We came to the point around 2008 that there was no chance to save this subspecies with the techniques we had available at that time".