Procedure Marks Milestone in San Diego Zoo Global’s Efforts to Save the Critically Endangered Northern White Rhino from Extinction
Researchers at the San Diego Zoo Institute for Conservation Research accomplished their first artificial insemination attempt on a southern white rhinoceros earlier this month—a key step in San Diego Zoo Global’s science-based, collaborative efforts to develop and perfect assisted reproductive technologies to save the critically endangered northern white rhino. Only three northern white rhinos currently remain on Earth.
“This procedure was historic for us, as it was our first time to attempt artificial insemination on a rhino,” said Barbara Durrant, Ph.D., director of Reproductive Sciences, San Diego Zoo Institute for Conservation Research. “The sperm had excellent motility, the procedure went very well, the rhinos involved are doing great and now we wait and hope for a pregnancy.” The artificial insemination took place July 6 on a 9-year-old rhino named Amani, at the San Diego Zoo Safari Park’s Nikita Kahn Rhino Rescue Center. Amani is one of six female southern white rhinos that were relocated to the Safari Park from private reserves in South Africa in November 2015, to serve as potential surrogates for a northern white rhino embryo in the future.
Keepers have worked for months to build positive relationships with the rhinos and have trained them to voluntarily walk into a chute for medical procedures. Durrant and Parker Pennington, Ph.D., postdoctoral associate, San Diego Zoo Institute for Conservation Research, have slowly acclimated the rhinos to allow researchers to perform transrectal ultrasound scans on a regular basis. These exams have allowed the researchers to collect detailed data on the complicated reproductive systems of the southern white rhino—and to learn more about the variability between the six rhinos, mapping ovarian dynamics, learning when they grow follicles, learning when they ovulate and more.
The procedure was not the first time artificial insemination has been performed on a rhino, but it was a first for San Diego Zoo Global researchers. Once it was determined that Amani was ovulating, fresh semen was collected from the Safari Park’s southern white rhino bull, Maoto. The collection was immediately taken to the Reproductive Sciences lab at the San Diego Zoo Institute for Conservation Research, where it was evaluated for concentration and motility. It was then transported to the Nikita Kahn Rhino Rescue Center, where the veterinary and animal care teams had prepared the female rhino for the procedure. Pennington inserted a catheter into the rhino’s cervix, and the sperm was expelled. The entire procedure with the female rhino took less than 20 minutes.
The artificial insemination procedure provided an opportunity for researchers to learn more about the intricacies of rhino reproduction, and to learn whether Amani is able to conceive and carry a calf to term—a crucial component of this conservation project. “It is very important for Amani and the other five rhinos to get pregnant when they’re young,” Durrant said. “Just like human females and other mammals, the older they are, the more difficult it can be to conceive.” Durrant added, “Pregnancy is not only important for the individual rhino’s reproductive health, but also when we make northern white rhino embryos, we would never risk putting a precious northern white rhino embryo into the uterus of a female who was not proven to be reproductively fit.”
Scientists will not know the result of this artificial insemination effort for many weeks. They will begin doing ultrasound scans on the rhino in the next two weeks, examining both uterine horns for evidence of a fetus, which may not be visible until it is several weeks old.The rhino’s ovaries will also be examined by ultrasound to confirm the presence of a corpus luteum, the structure formed after ovulation. In addition, analysis of Amani’s hormone levels will be closely monitored as an indicator of pregnancy. A rhino’s gestation period is 16 months. If the procedure was successful and Amani is able to carry the calf to term, the first southern white rhino calf born at the Nikita Kahn Rhino Rescue Center could arrive around November. Even if the procedure does not prove to be successful, the data collected leading up to this attempt will be extremely valuable for future work.
To reach the ultimate goal of successfully producing a northern white rhino, multiple steps must be accomplished. One of the first steps involved sequencing the genome of the northern white rhino to clarify the extent of genetic divergence from its closest relative, the southern white rhino. Another step requires conversion of cells preserved from 12 individual northern white rhinos in the San Diego Zoo Institute for Conservation Research’s Frozen Zoo® to stem cells that could develop into sperm and eggs—a process successfully begun in the laboratory of Jeanne Loring, Ph.D., of The Scripps Research Institute, with details of the process published in 2011.
Reproductive options include artificial insemination, in vitro fertilization and embryo transfer, with the southern white rhinos serving as surrogates for northern white rhino embryos. The reproductive system of rhinos is very complex, and there is still much to be learned. There are many challenges ahead, but researchers are optimistic that a northern white rhino calf could be born from these processes within 10 to 15 years. This work also may be applied to other rhino species, including critically endangered Sumatran and Javan rhinos.
Only three northern white rhinos remain in the world after the Nov. 22, 2015 death of Nola, an elderly 41-year-old northern white rhinoceros at the San Diego Zoo Safari Park. The northern white rhino is the world’s most critically endangered rhino, and the three that remain reside at the Ol Pejeta Conservancy in Kenya.