Scientists will be watching closely to see if the rhino named Victoria can carry her calf to term over 16 to 18 months of gestation.
If she does, researchers hope someday she could serve as a surrogate mother and could give birth to the related northern white rhino, whose population is down to two females after decades of decimation by poachers. The mother and daughter northern white rhinos that live in a Kenya wildlife preserve are not capable of bearing calves.
The last northern white male rhino, named Sudan, was euthanized in March at the Kenya preserve because of ailing health related to his old age.
Victoria is the first to become pregnant of six female southern white rhinos the San Diego Zoo Institute for Conservation Research is testing to determine if they are fit to be surrogate mothers. If they pass the testing, they could carry northern white rhino embryos sometime within the next decade as scientists work to re-create northern white rhino embryos.
There are no northern white rhino eggs so creating an embryo would require using genetic technology.
The San Diego Zoo Institute for Conservation Research has the cell lines of 12 different northern white rhinos stored in freezing temperatures at its "Frozen Zoo."
Scientists hope to use frozen skin cells from the dead northern white rhinos to transform them into stem cells and eventually sperm and eggs. Then the scientists would use in vitro fertilization to create embryos that would be put in the six female rhinos.
"The confirmation of this pregnancy through artificial insemination represents an historic event for our organization but also a critical step in our effort to save the northern white rhino," said Barbara Durrant, director of reproductive Sciences at the San Diego Zoo Institute for Conservation Research.
But more challenges lie ahead, with artificial insemination of rhinos in zoos rare so far and resulting in only a few births.
Victoria is a healthy 3,747-pound (1,700-kilogram) rhino estimated to be 7 years old.
She and the other five female rhinos that range in age from 4 to 7 years old were all born in the wild and relocated to San Diego's Safari Park in 2015. Scientists will be perfecting artificial insemination techniques and embryo transfer techniques on the females, which undergo weekly ultrasounds. Durrant recently spotted the beginning of tiny limbs of Victoria's baby during her recent ultrasound. She is two months pregnant.
"We will know that they have proven themselves to be capable of carrying a fetus to term before we would risk putting a precious northern white rhino embryo into one of these southern white rhinos as a surrogate," Durrant said.
The ultimate goal - which could take decades - is to create a herd of five to 15 northern white rhinos that would be returned to their natural habitat in Africa.
Some groups have said in vitro fertilization is being developed too late to save the northern white rhino, whose natural habitat in Chad, Sudan, Uganda, Congo and Central African Republic has been ravaged by conflicts in the region. They say the efforts should focus on other critically endangered species with a better chance at survival.
The southern white rhino and another species, the black rhino, are under heavy pressure from poachers who kill them for their horns to supply illegal markets in parts of Asia.
There are about 20,000 southern white rhinos in Africa.
This version corrects that there are no frozen northern white rhino eggs, not a limited amount of eggs, and corrects weight of Victoria to 3,747 pounds not 747 pounds.
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