Najin and Fatu are the last remaining northern white rhinos in the world. The mother and daughter live at the Ol Pejeta Conservancy in Kenya. Their horns have been sawed off at the base to make them less attractive to poachers, whose ceaseless efforts have driven the subspecies to the brink of extinction. Armed guards patrol the grounds, dedicated to keeping the animals safe.
On the other side of the world, the San Diego Zoo Wildlife Alliance is collaborating with a host of international organizations in a desperate bid to keep the northern white rhino from going the way of the baiji and the Pyrenean ibex. Scientists are exploring in vitro fertilization, ovum pickup, and other techniques in the hope of one day creating northern white rhino embryos, which will be placed in southern white rhinos for gestation. It is a truly remarkable endeavor—and veterinarians are playing a critical role.
The San Diego Zoo Safari Park boasts one of the largest captive populations of white rhinoceroses in the world, currently more than 20. In 2019, a southern white rhino, conceived through artificial insemination, was born there, an important first step in using similar techniques to save the closely related northern white rhino.
According to Barbara Durrant, PhD, director of reproductive sciences for the San Diego Zoo Wildlife Alliance, the zoo’s international outreach efforts to create embryos in the lab may be the last best hope for the northern white rhino’s survival—but it will not be easy. One of the greatest challenges is ovum pick-up (OPU), a skill possessed by only a handful of people worldwide. The San Diego Zoo Wildlife Alliance is collaborating with Morne de la Rey, BVSc, director of Embryo Plus South Africa, who perfected the technique for rhinoceroses.
Scientists from San Diego Zoo Wildlife Alliance have traveled to South Africa to observe Dr. de la Rey’s work, and in March 2020, de la Rey visited the San Diego Zoo Safari Park to assist with OPU on four southern white rhinos. The eggs will be matured, fertilized by intracytoplasmic sperm injection, then cultured through development of the blastocyte stage, the last stage before implantation into a surrogate uterus.
“We are not in this to produce the first northern white rhino calf or even a couple of calves,” notes Dr. Durrant. “We’re in it for the long run. It will be decades before this project is successful in placing the northern white rhino back in the wild.”
An essential 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 the cells can be converted to stem cells that could develop into sperm and eggs.
“Some of the northern white rhino cells have been in the freezer for 20 years,” Durrant says. “Those animals have been long gone, but we have their genetic material, giving us the potential to bring back northern white rhinos that never reproduced in their lifetime.”
Several organizations and institutions around the world are collaborating with the San Diego Zoo Wildlife Alliance on the northern white rhino initiative, explains Durrant. They include the Kenya Wildlife Service; the Leibniz Institute in Berlin, Germany, and a laboratory in Italy that is conducting research on rhino embryo production, among others.
Veterinarians, understandably, also play a vital role in the San Diego Zoo Wildlife Alliance’s effort to save the northern white rhino. “One of our responsibilities is performing anesthesia on rhinos, which involves intubation and ventilation. That’s a pretty challenging procedure not every institution does,” explains Lauren Howard, DVM, DACZM, director of veterinary services. “We also monitor their health through laboratory results, fecal results, and that kind of thing. We have also done some pharmacokinetic studies on some of the anesthesia we do in rhinos, and we’ll work with pharmacologists on that.” In addition, the San Diego Zoo Wildlife Alliance has five veterinary pathologists who perform full postmortems on any rhinos that die, as well as biopsies and placental evaluation on all newborn rhinos.
Thinking outside the box—or species
Sometimes other veterinary specialists are called upon for more specialized care. For example, an equine surgeon was consulted when one of the park’s rhinos broken a toe. Another equine surgeon assisted in the care of a female rhino that exhibited an abnormal reproductive anatomy.
“We’re constantly extrapolating and asking, what’s the closest domestic animal model?” Dr. Howard explains. “If we have a sick tiger, a cat internist is perfect because a tiger is really just a big cat. For rhinos, we use the horse as the domestic model because evolutionarily, they’re kind of on the same tree. Their height, their digestive tracts, their oral cavities are all relatively similar, so the equine folks are the ones we turn to most frequently.”
The initiative to save the northern white rhino stands tall on the shoulders of earlier efforts at 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 living birds, but captive breeding programs at the San Diego Zoo and elsewhere helped elevate its numbers to the point where hundreds have been returned to the wild. Another example is the Przewalski’s horse, an endangered species found in Mongolia. Working with a company in Texas, the San Diego Zoo Alliance recently produced the first Przewalski’s horse clone, which could go a long way in rescuing the species.
Saving the northern white rhino from extinction is the primary goal of the global initiative, but so, too, is the eventual return the species to its natural habitat. Of course, therein lie still more challenges.
“Reestablishing the species in its natural habitat is a goal I’m not sure I’ll see in my lifetime, but perhaps my daughters will,” Howard says. “We recognize we can make all the rhinos in the world, but if their habitat continues to disappear, we’ll have no place to put them. We’re working on what we can control most easily in the rhino part, but there’s going to be a much bigger issue establishing where ultimately these animals can be placed. In the meantime, we’re working on being ready to house a whole breeding herd of northern white rhinos here in the future, which, again, is still likely several decades off.”
Howard gets great personal satisfaction from her participation in the global effort to save the northern white rhino.
“Two things make it special,” she explains. “One is seeing a collaborative team pull together to accomplish a goal that is not immediately in front of us, but sometime in the future. That’s really nice to see because veterinarians spend so much time responding to emergencies. To put all of our collective skill, talent, and passion toward bringing back the northern white rhino is really warming to see.
“The other part is a connection to Najin and Fatu, and all of our colleagues across 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 try to figure out exactly how best to move forward. What we do in our own little corner echoes across the entire world. It’s a pretty neat feeling to know that we’re connected to those people who are guarding those northern white rhinos 24-7, protecting them from poachers. We’re all on the same team.”
Don Vaughan is an award-winning writer who frequently writes about veterinary-related topics.