Published: Jul 22, 2011 5:54 PM EDT
Updated: Jul 22, 2011 4:55 PM EDT

WASHINGTON (AP) - Giant panda Mei Xiang kept people guessing for months, but National Zoo veterinarians determined Friday that she had failed to become pregnant for the fifth year in a row even after a Chinese breeding expert tried to help her conceive.

Veterinarians announced Mei Xiang (may-SHONG) was experiencing a pseudopregnancy over the past several months, which means she ovulated but did not conceive. Animal keepers had been closely watching her behavior and monitoring her hormone levels because she had been eating less, staying in her den and cradling objects the way she did before she gave birth once before, in 2005.

 

Zoo scientists are concerned Mei Xiang may be infertile, said David Wildt, a senior scientist at the Smithsonian Conservation Biology Institute in Front Royal, Va., which has studied panda breeding with Chinese experts. Records from pandas worldwide dating back to 1985 show that pseudopregnancies are not rare, but consecutive ones are.

 

"It seems to be showing that if a giant panda has multiple years of pseudopregnancies, there's a high likelihood she will never succeed," he said.

Because of that, the zoo may seek to swap Mei Xiang out for another female. Smithsonian officials likely will begin talking with the Chinese within weeks about whether to continue trying to breed the current Washington pair - Mei Xiang and male panda Tian Tian (tee-YEN tee-YEN) - or perhaps move animals around within the Chinese panda program.

Wildt said the zoo needs healthy, reproductively viable animals to be able to contribute knowledge about the species. The current pair has never been able to breed naturally and only once with an artificial insemination.

"We are going to do something different," he said. "We don't intend to just let these animals go through this particular situation every year without trying to figure out what the issues are."

In January, the Smithsonian Institution signed new five-year, $2.5 million agreement with the Chinese to keep the beloved pandas in Washington. The agreement, announced during a lavish state visit by China's president, came with the caveat that one or both of the pandas could be switched out for others from China if they aren't able to breed.

It's difficult to determine when a panda is pregnant. Scientists say panda fetuses don't start developing until the final weeks of a gestation period. Mei Xiang stopped allowing animal keepers to perform ultrasound exams on her in early July.

The zoo was hopeful because a Chinese panda breeding expert helped zoo scientists artificially inseminate Mei Xiang in January. She and male panda Tian Tian had attempted to mate but weren't successful. Their only other cub, Tai Shan, was born July 9, 2005, and has since been sent to China.

Pandas have a long history intertwined with diplomacy between Washington and Beijing. The first panda couple, Ling-Ling and Hsing-Hsing, arrived in 1972 as a gift to the American people after President Richard Nixon's historic visit to China. Ling-Ling and Hsing-Hsing produced five cubs, but none survived.

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