For many reasons, breeding cheetahs is difficult. Because most of the species died leaving only a small number left to repopulate in the wild some 10,000 years ago, today’s cheetah population suffers from low genetic diversity. All living cheetahs are between 5 and 10 percent genetically alike; this similarity manifests itself in poor sperm quality, increased disease susceptibility and high infant mortality. To make matters worse females are picky about which mates they choose and have delicate reproductive cycles. If two unrelated female cheetahs are placed in the same living quarters, the stress can actually shut down one another's reproductive, or estrous, cycles. But even in non-stressful situations, female cheetahs' estrous cycles are extremely unpredictable. Adrienne Crosier, a biologist at the Smithsonian Conservation Biology Institute's Center for Species Survival who leads the cheetah breeding program, says they hesitate to call it a cycle because it is so difficult to track.
This is all unfortunate, because the world's fastest land mammal could use help breeding. The cheetah has been critically endangered for decades. Between 7,000 and 10,000 cheetahs are left in the wild—the majority in Africa—down from 100,000 in 1900, and habitat destruction and human conflict continue to decrease their numbers.
The good news is that scientists are making headway with assisted reproduction techniques that could help save the charismatic animal. On April 6, for example, scientists at the Smithsonian National Zoo's Center for Species Survival in Front Royal, Va., including Crosier, attempted to extract an older female's eggs. The plan was to fertilize the eggs in vitro and either freeze them for later use or transfer them into a younger female. It was the second attempt at harvesting eggs for a possible embryo transfer since June 2013. Although neither were successful, it is still a positive development, because what went wrong can be corrected for future attempts. Depending on how many females at the National Zoo reproduce naturally this year, Crosier says, she expects they will try another egg extraction in the next few months.
Biologists at the National Zoo are also making progress with artificial insemination. But the technique only results in pregnancies about 22 percent of the time. Crosier says she expects artificial insemination will be a reliable, viable option in about a decade—once scientists learn to use hormones to better control the estrous cycle, along with getting the timing right. Extensive cheetah sperm banks exist around the world. Laurie Marker, founder and executive director of the Cheetah Conservation Fund in Namibia, has obtained and frozen sperm samples from nearly 200 male cheetahs over the years that could be used to impregnate live females today or in the future. David Wildt, head of the Center for Species Survival, says about 10 to 20 percent of cubs at the National Zoo are and will continue to be produced by artificial insemination.
Finally, there’s genome sequencing, which could help scientists understand what genes account for specific diseases or debilitating characteristics. Stephen O'Brien, cheetah expert and chief scientific officer at Saint Petersburg State University's Theodosius Dobzhansky Center for Genome Bioinformatics, says he hopes the genome sequence will allow scientists to answer more questions about the cheetah than ever before, and help save the species.
Cheetah experts all agree that assisted reproduction is only a stopgap—O'Brien calls it an "emergency room technology”—and that real progress in saving wild cheetahs will have to involve restoring habitat and working with locals to prevent hunting or defensive killing. Crosier says she hopes reliable assisted reproduction can be a piece of the larger repopulation strategy. "We've had a big hand in the decline of a lot of species and I'm personally not willing to sit back and watch them disappear if we have the opportunity to save them."