A species conservation consortium has successfully implanted an artificially fertilized southern white rhinoceros embryo into a surrogate rhinoceros mother in Kenya. This is the world’s first pregnancy of a rhino following an embryo transfer. Although the surrogate mother and calf are now dead, the scientists hope to use the same technology to carry northern white rhino babies to term in the future. This could save the species, which is in acute danger of extinction.
Transferring an embryo into a surrogate mother is common in humans and animals such as horses and cows. A team from the scientific and species conservation consortium BioRescue has carried out extensive research to make this reproductive medicine method possible for rhinos – no easy feat for these wild animals, which weigh around two tons. The associated hope is to create rhino babies through artificial insemination and have them carried out in surrogate mothers. This would increase the number of rhinos’ rare offspring and could even save the northern white rhinoceros (Ceratotherium simum cottoni) from extinction – there are only two living specimens left. So far, the team has carried out 13 embryo transfers on rhinos, three in Kenya and ten in Europe. However, the surrogate mother has never had a stable pregnancy.
Successful embryo transfer in rhinos
In September 2023, the team in Italy once again created two in-vitro fertilized embryos from southern white rhinos (Ceratotherium simum simum) and then implanted them into the uterus of the rhino surrogate mother Curra of the same species at the Ol Pejeta station in Kenya. The eggs used to create the embryos came from a female southern white rhinoceros living in the Belgian zoo Pairi Daiza. The sperm used for fertilization came from a male from Salzburg Zoo, also a southern white rhinoceros. And this time an embryo actually implanted in the surrogate mother: the team discovered that she was pregnant while observing the female rhinoceros.
However, the surrogate mother Curra died unexpectedly around two months after the embryo transfer. Extreme rains had flooded the surrogate mother’s enclosure, washing Clostridia spores to the surface. The animal’s autopsy revealed poisoning by the toxin from these bacteria. At the same time, it was determined that Curra was pregnant with a 70-day-old, 6.4 centimeter long and therefore well-developed and viable male fetus. DNA analysis of the fetus confirmed this. “In the horse, the rhinoceros’s closest relative, fetal loss occurs most frequently in the first 50 days. “The development of this fetus suggests that the probability of a successful birth was over 95 percent,” explains Cesare Galli from the Italian veterinary clinic Avantea.
Although Curra’s death is a tremendous loss and meant the calf could not be carried to term, the pregnancy is a scientific breakthrough and the first evidence that embryo transfer is possible in rhinos. “It took many years for us to be successful. And we are overwhelmed that we now have proof that this technology works perfectly,” says Thomas Hildebrandt from the Berlin Leibniz Institute for Zoo and Wildlife Research.
Hope for the Northern White Rhinoceros
This finding now paves the way to applying the same technique to the closely related northern white rhinos. Unlike the southern subspecies, of which there are still around 17,000 animals, the northern species is already extinct in the wild. There are currently only two living northern white rhinos left in the world: Najin and her daughter Fatu. Both females live in the sanctuary in Kenya, but can no longer carry any embryos themselves. Ideally, however, they should take over the care of rhino babies born through surrogate mothers and teach them the social behavior of the species.
In order to produce offspring of the endangered species, sperm and other cells from deceased and the two still living northern white rhinos were stored in liquid nitrogen. Since 2019, the BioRescue team has already created 30 northern white rhinoceros embryos using artificial insemination and also cryopreserved them in liquid nitrogen. These embryos will now be implanted into surrogate mothers of the southern rhino subspecies and carried to term. With the successful detection at Curra, the team can now theoretically carry out the first embryo transfer with a northern white rhinoceros embryo. “We can succeed in two to three years,” says Hildebrandt.
However, new surrogate mothers must first be selected and waited until they are ready to conceive. However, this can only be recognized by the researchers through the mating behavior of a bull rhinoceros that wants to mate with the females. The team in Kenya uses a sterilized bull to avoid creating a natural pregnancy with a southern rhinoceros. However, the last such bull also died in the Clostridia outbreak. Only when a new bull is available can an embryo transfer with a northern white rhinoceros embryo take place.
Source: Leibniz Institute for Zoo and Wildlife Research (IZW) in the Forschungsverbund Berlin eV