Najin and Fatu are the last remaining northern white rhinos in the world. Mother and daughter live in Ol Pejeta Conservancy in Kenya. Their horns have been sawn off at the base to make them less attractive to poachers, whose tireless efforts have pushed the subspecies to the brink of extinction. Armed guards patrol the grounds to ensure the safety of the animals.
On the other side of the world, the San Diego Zoo Wildlife Alliance is working with a variety of international organizations to discourage the northern white rhino from following the path of the baiji and the Pyrenean ibex. Scientists are exploring in vitro fertilization, egg retrieval and other techniques in hopes of one day creating northern white rhino embryos to be placed in southern white rhinos for gestation. It’s a truly remarkable endeavor – and veterinarians play a crucial role.
The San Diego Zoo Safari Park has one of the world’s largest populations of captive white rhinos, currently more than 20. In 2019, a southern white rhino was born there, conceived through artificial insemination, an important first step in applying similar techniques to the closely related one Save northern white rhino.
According to Barbara Durrant, PhD, director of reproductive sciences at the San Diego Zoo Wildlife Alliance, the zoo’s international effort to grow embryos in the lab could be the northern white rhino’s last hope for survival — but it won’t be easy. One of the biggest challenges is egg retrieval (OPU), a skill only a handful of people worldwide possess. The San Diego Zoo Wildlife Alliance works with Morne de la Rey, BVSc, director of Embryo Plus South Africa, who perfected the technique for rhinos.
Scientists from the San Diego Zoo Wildlife Alliance traveled to South Africa to study the work of Dr. de la Rey, and in March 2020, de la Rey visited the San Diego Zoo Safari Park to assist the OPU with four southern white rhinos. The oocytes are matured, fertilized by intracytoplasmic sperm injection, and then cultured until the development of the blastocytic stage, the last stage before implantation in a replacement uterus.
“We don’t want to produce the first northern white rhino calf here, or even a few calves,” notes Dr. Durrant. “We are here for the long term. It will take decades for this project to be successful to reintroduce the northern white rhino into the wild.”
A key part of the initiative is the San Diego Zoo Wildlife Alliance’s Frozen Zoo, which cryogenically preserves living cells from more than 1,200 species, including 12 individual northern white rhinos. It is hoped that the cells can be turned into stem cells, which could develop into sperm and egg cells.
“Some of the northern white rhino cells have been in the freezer for 20 years,” says Durrant. “These animals are long gone, but we have their genetic material, which gives us the potential to bring back northern white rhinos that never bred in their lives.”
Several organizations and institutions around the world are collaborating with the San Diego Zoo Wildlife Alliance on the northern white rhino initiative, Durrant explains. These include the Kenya Wildlife Service; the Leibniz Institute in Berlin, Germany, and a laboratory in Italy which, among other things, conducts research on the embryonic production of rhinos.
Veterinarians understandably also play an important role in the San Diego Zoo Wildlife Alliance’s efforts to save the northern white rhino. “One of our tasks is anesthesia in rhinos, which includes intubation and ventilation. It’s quite a challenging process that not every institution does,” explains Lauren Howard, DVM, DACZM, Director of Veterinary Services. “We also monitor their health using lab results, fecal results and the like. We’ve also done some pharmacokinetic studies on some of the anesthetics we use in rhinos, and we’ll be working with pharmacologists on that.” In addition, the San Diego Zoo Wildlife Alliance has five veterinary pathologists who will perform full autopsies, biopsies, and placental examinations on all rhinos that have died perform on all newborn rhinos.
Sometimes other veterinarians are called in for more specialized care. For example, a horse surgeon was consulted when one of the park’s rhinos broke a toe. Another equine surgeon helped care for a female rhino that had abnormal reproductive anatomy.
“We’re constantly extrapolating and asking what’s the next pet model?” Howard explained. “If we have a sick tiger, a feline internist is perfect because a tiger is really just a big cat. For rhinos, we use the horse as the domesticated model because they are evolutionarily on the same tree. Their size, their digestive tracts, their oral cavities are all relatively similar, so we turn to the horse people most often.”
The initiative to save the northern white rhino builds on previous efforts by the San Diego Zoo Wildlife Alliance to save endangered species from extinction. One of the most successful examples is the California condor, Durrant says. At its nadir, the species had fewer than 20 live birds, but captive breeding programs at the San Diego Zoo and elsewhere have helped increase their numbers to the point where hundreds have returned to the wild. Another example is the Przewalski’s horse, an endangered species found in Mongolia. In partnership with a Texas company, the San Diego Zoo Alliance recently produced the first Przewalski’s horse clone that could go a long way towards saving the species.
Saving the northern white rhino from extinction is the primary goal of the global initiative, but so is the eventual return of the species to its natural habitat. Of course, there are other challenges as well.
“Reintroducing the species to its natural habitat is a goal I’m not sure I’ll achieve in my lifetime, but maybe my daughters will,” says Howard. “We know we can make all the rhinos in the world, but if their habitat continues to disappear, we won’t have room for them. We’re working on what’s easiest for us to control in the rhino part, but there will be a much bigger problem determining where these animals can ultimately be placed. In the meantime, we are working to house an entire herd of northern white rhinos here in the future, which again is likely several decades away.”
Howard derives great personal satisfaction from her participation in the global effort to save the northern white rhino.
“Two things make it special,” she explains. “You see a team working together to achieve a goal that is not immediately ahead of us, but sometime in the future. It’s really nice to see because veterinarians spend so much time responding to emergencies. Putting all of our collective skill, talent and passion into bringing back the northern white rhino is truly heartwarming to watch.
“The other part is a connection to Najin and Fatu and all our colleagues around the world who are working hard to save the species. We’re not in a bubble. Several different groups are working in parallel, doing our best to pool resources and figure out how best to move forward. What we do in our own little corner resonates around the world. It feels pretty good to know that we are connected to the people who guard these northern white rhinos 24/7 and protect them from poachers. We are all on the same team.”
Don Vaughan is an award-winning writer who writes frequently on veterinary topics.