"It is a terrible loss. Nabiré was the kindest rhino ever bred in our zoo. It is not just that we were very fond of her. Her death is a symbol of the catastrophic decline of rhinos due to a senseless human greed. Her species is on the very brink of extinction," said Přemysl Rabas, the director of the zoo.

Nabiré was born on November 15, 1983 at the Dvůr Králové Zoo as one of the only four northern white rhinos ever bred in captivity. She spent all her life in Dvůr Králové. "The pathological cyst inside the body of Nabiré was huge. There was no way to treat it," said Jiří Hrubý, a rhino curator of the zoo.

In the wild, the northern white rhinos (NWR) were poached to extinction. Their slaughter has been driven by the demand for their horn in some countries of East Asia and the Arabian Peninsula.

Thanks to 40 years of breeding efforts, the Dvůr Králové Zoo prolonged the very presence of NWR on this planet. The initial group was brought to Dvůr Králové Zoo in 1975 from southern parts of Sudan. The group consisted of two males and four females. Two individuals of the founding group are still alive – a male Sudan lives in Ol Pejeta in Kenya and a female Nola is located in San Diego.

In addition to these, there are two more northern white rhinos, females Nájin and Fatu, both of them born at the zoo in Dvůr Králové. Together with a male Sudan, they were translocated in 2009 to Kenya.

Nabiré was one of the animals that participated in Dvůr Králové Zoo efforts to breed these rarest rhinos in the world. Nabiré could not conceive naturally due to a large amount of cysts in her utero. Her left ovary, however, appeared to be healthy, so it was hoped she might become a donor of eggs for in vitro fertilization which could result in an artificially made embryo.

For this reason, her potentially healthy ovary was immediately after the death removed and taken to a specialized laboratory in Italy. Tissue samples that could be used for scientific research and reproduction work were collected as well.

Dvůr Králové Zoo with its partners continues with the efforts towards survival of the northern white rhino. "It is our moral obligation to try to save them. We are the only ones, perhaps with San Diego Zoo, who have enough of collected biological material to do so. We are aware that our chances are slim, but the hopes are still alive," said Přemysl Rabas, the director of the zoo.

Apart from its own breeding program, Dvůr Králové Zoo shifted part of a NWR group to the San Diego Zoo in 1989 to reduce the risk of possible decimation of the only captive animals held at a single location due to unexpected healthy problems.

Unfortunately, the females did not conceive in San Diego and Dvůr Králové Zoo remained the only facility where northern white rhinos managed to reproduce. But even in Dvůr Králové their rate of reproduction was too low. In addition to research of hormonal cycles, which has taken place in Dvůr since the 1980s, the zoo began to cooperate with the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin on artificial techniques of reproduction in 2001.

All females were stimulated with hormonal implants and females Nájin and Fatu were repeatedly artificially inseminated with semen of northern males in 2006 and 2007.

After unsuccessful attempts with artificial insemination, the zoo decided to go for a next step – in December 2009, the zoo transported two males and two females to Ol Pejeta Conservancy in Kenya. It was hoped that natural surroundings close to their original habitat could give them an impulse that would prompt their breeding. Although the acclimatization of the animals went well, the hormonal cycles of the females improved and repeated mating was observed, unfortunately, no pregnancy occurred.

Thus, the team from IZW Berlin with support from the Dvůr Králové Zoo and other partners currently aims at developing a robust protocol to optimize a procedure of harvesting and maturing oocytes, fertilization of oocytes and following embryo transfer for a southern white rhino. When the process is standardized on close relatives of northern white rhinos, the team will aim at harvesting oocytes from the last northern white rhino females, mature oocytes, fertilize them with northern white rhino semen, generate embryos on a large scale and cryo-preserve them or transfer them directly into a surrogate mother of a southern white rhino origin.

According to health examination that took place at the end of 2014, the two females in Ol Pejeta Conservancy, Nájin and Fatu, could become donors of eggs for the experiment. Also, Dvůr Králové Zoo collaborates with the San Diego Zoo Global and other partners on challenging task to save the northern white rhino by using advanced cellular technologies.