Scientists have created hybrid white rhinoceros embryos in the lab using frozen sperm from extinct male northern white rhinoceros.

Their work is the latest step in an attempt to bring the most endangered mammal on Earth back from the brink.

Only two female northern white rhinoceros (Ceratotherium simum cottoni) still exist.

The last male northern white rhino, Sudan, died earlier this year.

Thomas Hildebrandt, a global pioneer in reproductive science,  has watched the decline of the subspecies of the iconic animal in the past 20 years.

“We may need a little bit of luck, but I think what we can demonstrate already is quite impressive.”

Professor Hildebrandt and colleagues have shown for the first time that artificial reproduction techniques can be successfully used to create rhino embryos, they report in the journal Nature Communications.

They have also proven the ability to generate embryonic stem cells, which could potentially produce more eggs and sperm.

Creating embryos using frozen sperm

Artificial reproduction techniques have never been attempted before in the rhino, study co-author Marilyn Renfree said.

“This is the first time it’s been done in this species because it’s a very large animal and has a particular shape to its reproductive tract,” Professor Renfree of the University of Melbourne said.

About the size of an SUV, the white rhinoceros is the largest of all rhino species.

There are two subspecies: the almost-extinct northern white rhinoceros, and their cousins, the southern white rhinoceros.

Southern white rhinoceros will play surrogate mothers to embryos created through artificial reproductive technologies. Photo: Getty

Using a specially designed tool, the team harvested eggs from live southern white rhinos and combined them with frozen sperm that had been previously collected from northern white males and stored in sperm banks.

The frozen sperm was a bit sluggish at first, but after zapping it with electricity the team were able to successfully produce early-stage embryos known as blastocysts.

The team also used eggs and sperm from the southern white rhinoceros to create pure embryos.

Three of the early-stage embryos – two hybrid and one pure – have been cryofrozen.

The team plan to implant embryos into southern white rhino females to see if the surrogate mothers can carry a pregnancy to term.

“We have several of these embryos in high quality,” Professor Hildebrandt said.

The quest to create a northern white rhino baby

While this phase of the work aims to create hybrid calves, the goal of the project is to create a pure northern white rhino calf.

To do this, the team plan to harvest eggs from the last two females –Sudan’s daughter Najin and granddaughter Fatu, which live at the Ol Pejeta Conservancy in Laikipia national park in Kenya.

Fatu and Najin graze at the Ol Pejeta Conservancy in Laikipia national park, Kenya. Photo: AAP

“Before we collect the [eggs] … we need proof of concept that the embryo transfer with hybrid embryos is working,” Professor Hildebrandt said.

It is also unclear at this stage whether or not Najin and Fatu will have viable eggs, he said.

“Nobody has any idea about how they look inside. The younger female is 18, the older female is 26, so we’re running out of time.”

If the team can produce a pure white rhino calf, they could use the stem cell technology, which they used in this paper, to produce a line of northern white rhino eggs from embryonic stem cells.

“We need one or two northern white rhino female calves, then I think we are all go for sure,” Professor Hildebrandt said.

Professor Renfree said the work still had a long way to go, but it was a proof of principle.

“This is a stunning result,” she said.

“I don’t know if it’ll ever save the northern white rhino … but it certainly is a great step in the right direction.”

Should we bring animals back from near extinction?

While powerful in their scope, using artificial technologies to save near-extinct species, such as the northern white rhinoceros is controversial.

Conservation biologist Guy Castley of the Environmental Futures Research Institute at Griffith University applauded the team’s work.

“They’ve made some big strides in advancing what has been known about artificial reproductive technologies and using IVF potentially to rescue genetic material for a species on the brink of extinction,” Dr Castley said, who was not involved in the research.

But, he said, it does not address the bigger picture issues such as poaching and habitat loss that led to demise of the species in the first place.

“If we were able to secure those rhinos they may end up with a life kept in captivity because there’s just no space for them to go in their natural environment.”

It would also take time to build up a viable herd, Dr Castley said, who has worked with the southern white rhino in the past.

“You’d have to have multiple surrogate females and multiple [embryos] that you can then generate an insurance population,” he said.

“Once that happens, the rhinos would have to get to an age where they would be able to breed, so you’re looking at 10 years old.”

With only two live northern white females and sperm from four males available, genetic diversity has been raised as another issue.

But Professor Hildebrandt is optimistic boosting the genetic gene pool could be achieved by using stem cell technology to create eggs from frozen skin cells of 12 different northern white rhinos stored in cell banks around the world.

The technique, inspired by the work of the 2012 Nobel Prize winners, has been proven to work in mice by Japanese scientist Katsuhiko Hayashi, another member of the team.

“The southern white rhino was nearly extinct at the beginning of the 20th century, there were less than 50 individuals left and now we have more than 20,000,” Professor Hildebrandt said.

“And their genetic variation is lower than what we have with these 12 samples.”

Last-ditch effort could save other species

Professor Renfree said having low biological diversity was better than not having the animals at all.

“There have been many, many, many attempts to save rhinos by classical conservation methods and they’ve all failed,” she pointed out.

“This is the last possible step to save these guys.”

It is estimated that there are fewer than 100 Sumatran rhinoceros left in the wild. Photo: Getty

The technology and the techniques developed by the team could also be used to help prevent the extinction of other large animals and related species such as the Sumatran rhino.

“If you really want to be successful you start doing it a lot earlier than the last few animals.”

Dr Castley agreed.

“I would hate to see another species go extinct,” he said.

“We weren’t able to take control of the situation and read the signs fast enough to do anything for the northern white rhino … but we might still be able to do something for other threatened species.

“If this research can assist with the progression and the development of novel technologies that can assist with those efforts then we should be using that,” he said.

-ABC