They are the last of their kind: only two examples of the northern white rhinoceros exist in the world. The elder of the two females, Najin, are now retiring from conservationists and scientists: the 32-year-old rhinoceros cow no longer has to donate egg cells. The stress placed on the animal by the procedure does not outweigh the possible successes of breeding the species.
Najin and her daughter Fatu are the only two surviving representatives of the northern white rhinoceros (Ceratotherium simum cottoni), a rhinoceros species that has been extinct in the wild since 2008. Most of the last populations of this species, which were found in northern Congo, among others, were largely exterminated by poachers in the 1980s. Najin, Fatu and the last male Sudan come from a safari park and should produce offspring as part of a breeding program. But that didn’t work and Sudan died in 2017.
Artificial insemination to save the species
Since then, conservationists and veterinarians have been trying to save the species using the most modern methods of reproductive medicine: egg cells are removed from the two rhinoceros and fertilized with the sperm of the rhinoceros bull Sudan, which was frozen before his death. “This procedure is absolutely new in rhinos, and although it is carried out in a highly professional and safe manner by the world’s leading scientists and veterinarians on the BioRescue team, it poses risks for the animals,” explains Jan Stejskal, Director of International Projects in the Dvur Králové Safari Park. To do this, the rhinoceros cows have to undergo a hormonal treatment that promotes the maturation of the egg cells in their ovaries. Then the eggs are removed from them under general anesthesia.
This process has so far resulted in the production of three embryos, all of which were conceived with eggs from Najin’s daughter Fatu. The embryos, which are currently still on ice, are to be carried by a southern white rhinoceros as surrogate mother in the future. In contrast, with Najin, who was already quite old at 32, the attempts were less successful: “The egg collection at Najin only delivered a few egg cells, none of which could be successfully fertilized to produce an embryo,” reports Stejskal. Ultrasounds have also shown that Najin has several small, benign tumors in the cervix and uterus, as well as a cyst in the left ovary. This could explain why the egg retrieval was not so successful from her.
“Retired” for ethical reasons
In view of these findings and the unpromising results of the egg retrieval, the BioRescue consortium has decided to retire Najin: “Removing an individual animal from a protection program due to animal welfare concerns is usually not a question that takes a long time to think about.” , explain the veterinarians Frank Göritz from the Leibniz Institute for Zoo and Wildlife Research and Stephen Ngulu from Ol Pejeta Conservancy. “But when a single individual makes up 50 percent of the population, this decision is reconsidered several times because it could have a significant impact on the prospects of the conservation program.”
The decisive factor for this was the weighing of ethical concerns regarding the welfare of the rhinoceros against the interests of species protection. “We are aware of the fact that we are pushing the limits of what is feasible in nature conservation and this also requires thinking about ethical and moral consequences,” says BioRescue project manager Thomas Hildebrandt from the Leibniz Institute for Zoo and Wildlife Research. “We are convinced that we shouldn’t do anything we could do just because we can.” Najin should remain an important part of the mission as a representative of her kind and by passing on social knowledge to future descendants.
Stem cell technology as a second mainstay
This means that the program to save the northern black rhinoceros still has a female who can deliver egg cells: Najin’s daughter Fatu. It should continue to deliver egg cells, but the scientists of the BioRescue project are also relying on stem cell-based techniques: Pluripotent stem cells induced by a kind of genetic reprogramming can be grown in the laboratory from freshly removed or frozen tissue from Sudan, Najin and Fatu, for example some skin cells.
These cells, which are returned to their embryonic state, could then be used to breed egg cells and sperm. Although such stem cell-based techniques are still in their infancy when it comes to rhinoceros reproduction, the scientists hope that this will give them another chance to save the northern white rhinos.
Source: Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW)