Though more female rhinos than males survive, it's actually eggs that are in short supply, researchers told Live Science in June. Northern white rhinos ovulate only one egg at a time every 30 days or so, which makes collecting mature eggs a slow process. Immature eggs can be harvested from the ovaries, but researchers have to develop techniques to mature those eggs in the lab.
Scientists also have to develop IVF procedures that work on rhinos, which has never been done before.
"Every species requires different culture conditions, and that's because the actual conditions in the uterus in the animal are different," said Barbara Durrant, director of reproductive physiology at the San Diego Zoo Institute for Conservation Research.
Durrant and her colleagues around the world are trying to make use of research on horse IVF, as horses are close relatives of rhinoceroses. But IVF is also difficult in horses, Durrant said in June.
The Dv?r Králové Zoo plans to continue its efforts to save the subspecies.
"It is our moral obligation to try to save them," zoo director P?emysl Rabas said in a statement. "We are the only ones, perhaps with San Diego Zoo, who have enough of collected biological material to do so."
The loss also struck Nabiré's keepers on a personal level.
"Nabiré was the kindest rhino ever bred in our zoo," Rabas said.
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