An international team of scientists looking to save the Northern White Rhino from extinction has cultivated a record number of viable embryos in a sub species crucial to its survival. The next step in the rescue effort, coordinated in part by the Czech zoo in Dvůr Králové, is to transfer the embryos to surrogate mothers.
The Northern White Rhino can no longer survive on its own as a species because the last living individuals are both females. To perpetuate the species’ existence, their immature egg cells must be collected, fertilised with the frozen sperm of deceased bulls, and implanted back in the womb of the original donor or of a close relative, the Southern White Rhino.
The latest such “advanced assisted reproduction technology” (aART) effort took place at a zoo in Germany, where eggs were extracted not from a northern but from a southern white rhino, a seven-year-old named Makena. Jan Stejskal, director of communication and international projects at Safari Park Dvur Králové and coordinator of international efforts to save the Northern White Rhino, explains the significance of the development.
“There are only two female Northern White Rhinos left in the world. The Serengeti Park in Hodenhagen, Germany, extracted twelve implanted eggs from Makena, from which four are viable embryos. It is the greatest success in the past five years of the rescue project.”
The two last Northern White Rhinos females, called Najin and Fatu, were both born in the Dvůr Králové zoo and transferred to Kenya in 2009. In 2014, a health check determined neither can conceive naturally, and since then the Czech zoo has been cooperating with a team of international experts to collect their eggs and then produce a pure Northern White Rhino embryo.
A lot can still go wrong. Problems with natural reproduction are often a major factor in the decline of wildlife populations, both in the wild and in human care. Southern White Rhinos in European zoos, such as Makena, also tend to have reproduction problems. Jan Stejskal again:
“It’s important to note that previously, we only had three Northern White Rhino embryos. To ensure a successful implant with surrogate mothers, the transfer must be done many times… But the experience gained through such work in European zoos should help ensure the survival of both subspecies.”
Working together towards that goal are the BioRescue team –comprised of the Dvůr Králové zoo, the Leibniz Institute for Zoo and Wildlife research in Berlin, the Avantea Laboratory in Italy (where the fertilisation takes place), and Ol Pejeta Conservancy in Kenya, along with the Eastern African country’s national wildlife service.
Despite the advances, it may be several years yet before another Northern White Rhino calf is born. Even if an embryo transfer is successful, a rhino pregnancy lasts for 16 months, and not all are brought to term.