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Where Do Zoo Babies Come From?
Comments () | Published September 1, 2009
Over the next decade, Monfort and his team studied P-horse reproduction. They’ve charted estrus cycles in mares to determine the best time for breeding. They performed the first successful reverse vasectomy, allowing valuable genes of a P-horse stallion to reenter the population. Last year, the zoo saw the births of two foals—the first in nine years. Another was born in July.

Thanks in part to the zoo’s work with the captive population, P-horses began to be reintroduced into the wild in 2001. Today more than 400 roam in sanctuaries in China, Mongolia, and Kazakhstan. Scientists in the National Zoo’s satellite-imagery lab monitor the horses. Last year, the species’s status was downgraded from “extinct in the wild” to “critically endangered.”

“Research is sometimes mind-bogglingly slow,” says Collins. “But it feels good to see our hard work finally pay off.”


With every discovery comes a new challenge. Monfort says the next step is to develop tools to make breeding easier. Moving animals from one zoo to another for breeding can be risky and expensive, and it doesn’t always result in pregnancy.

Lots of techniques could be helpful, such as artificial insemination, but scientists have found that methods that work with one species don’t necessarily translate to others. Wynne Collins has tried for years to artificially inseminate the zoo’s Przewalski’s horses, but so far she’s been unsuccessful. In Asian elephants, the technique has yielded results—Kandula, the only Asian elephant born at the National Zoo, was the product of artificial insemination.

So was the zoo’s poster cub, Tai Shan, the only giant panda born at the National Zoo. His mother, Mei Xiang, was artificially inseminated in March 2005.

Giant pandas are notoriously hard to breed in captivity—doing so requires a perfect storm of environment and timing—and they’re prone to pseudopregnancies. During false pregnancy, a panda’s hormone levels and behavior are identical to the patterns in a real pregnancy. Scientists can’t determine a pseudopregnancy until the animal’s hormones return to normal without a birth. This makes early pregnancy detection very hard.

Tai Shan was born on July 9, 2005, much to the delight of zoo scientists. He was the zoo’s first giant panda cub to survive birth and the first to result from artificial insemination.

Another useful tool is a semen-freezing technique called sperm cryopreservation. It was first used for cattle in the 1940s but has been adapted for wildlife over the last 30 years. Budhan Pukazhenthi is at the forefront in developing the method for the Eld’s deer, an endangered species from Asia that looks like a heartier version of the white-tailed deer. The goal is to build a library of samples that can be used now and in the future to mate ideal pairs. Says Pukazhenthi: “You can reintroduce genes into a population long after an animal is gone.”

The concept of freezing semen is pretty basic—mix it with chemicals to prevent icing, freeze it, then thaw it and hope the cells aren’t damaged—but the trick is finding the right combination of chemicals for each species. Scientists have been able to create workable compounds for the Eld’s deer and a number of wild cats, but Pukazhenthi says the process is trial and error. He’s currently working on sperm cryopreservation for P-horses and Asian elephants.

The technique has seen impressive results for the black-footed ferret, one of the world’s most endangered animals. Indigenous to the Great Plains, the species was considered extinct until 1981, when a small population was found in Wyoming.

The National Zoo was the first facility outside Wyoming to take part in a breeding program. For more than ten years, Pukazhenthi and other scientists have maintained a Black-Footed Ferret Genome Resource Bank, a repository of semen from the most valuable males. Last year, they successfully inseminated two ferrets with frozen sperm—specimens taken more than a decade ago from males that died in 1999 and 2000.

With the help of an SSP, the genome bank, artificial insemination, and other breeding methods, the zoological community has brought the population of black-footed ferrets back from 18 in 1981 to more than 800 in the wild today.

“It’s not black magic,” says Pukazhenthi. “There are times when we get discouraged and times when we have success. All of those experiences serve as steppingstones for the next time.”

Like Pukazhenthi, Jon Ballou downplays his contributions. He talks at length about breeding programs and genetics but clams up when it comes to discussing his impact on zoo science. Asked why he didn’t name the mean-kinship equation after himself, he laughs and says shyly, “I didn’t even think of it.”

How does it feel to know he’s helped save hundreds of wildlife species from extinction?

“Well,” he says slowly, as if searching for the right words, “I guess I feel useful.” 

For Math and Science Fans

Jon Ballou’s “mean kinship” equation helps zoos manage their breeding programs. The formula measures the relationships among animals. In mathematical terms, it’s expressed like this:

MK(i) = Sum[K(ij)] / N

MK(i) is the mean—or average—kinship of individual i.

K(ij) is the kinship between animals i and j.

N is the number of animals in the population.

Individuals are assigned numerical values based on how closely they’re related to other animals in the population. For example, siblings i and j have a kinship (K) of 0.25; a grandchild has a kinship to its grandparent of 0.125. Unrelated animals are assigned a value of zero.

Once the relationships are tallied for each pair of animals in a group, you add the numbers and take the average. The animals with the lowest mean-kinship value are the most valuable. Animals with the highest kinship averages have usually been bred enough times, and their genes are well represented.

Zoo scientists aim to achieve genetic diversity, so they restock the pool with genes that are underrepresented. Based on the mean-kinship formula, scientists aim to breed only those animals with the lowest genetic kinship. The process helps zoos minimize inbreeding.

This article first appeared in the September 2009 issue of The Washingtonian. For more articles from that issue, click here.


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Posted at 12:00 AM/ET, 09/01/2009 RSS | Print | Permalink | Comments () | Articles