Zoo scientists believe the panda might have been pregnant and lost the fetus early in the pregnancy,according to a zoo press release.
“Everyone was hopeful for a cub this year,but at the same time we learned so much more about pandas,and that's really why we do this,” said Zoo spokeswoman Sarah Taylor.
Veterinarians were never able to confirm whether she was ever pregnant or simply going through a pseudopregnancy. That's a common state in which pandas exhibit hormonal changes and behaviors indicating they are pregnant when they're not.
Scientists artificially inseminated Mei Xiang in March with semen from Tian Tian,the zoo's adult male panda,and she went through hormone changes and displayed pregnancy-like behaviors throughout the summer.
Taylor said that if a panda is going through a pseudopregnancy,she will usually stop displaying maternal behaviors as her hormone levels go back to normal. Mei Xiang's hormone levels returned to normal last week,meaning she can't be pregnant,but her pregnancy behaviors have continued.
“We weren't sure,” Taylor said. “She definitely kept us on our toes this year.”
Scientists performed ultrasounds on Mei Xiang,but ultrasounds cannot reach a panda's entire reproductive tract. Though an ultrasound can sometimes detect a cub if it is there,it often can't.
The ultrasounds were inconclusive. That's in part because panda cubs weigh 3 to 5 ounces at birth and are about the size of a stick of butter. Mei Xiang weighs 250 pounds.
Mei Xiang and Tian Tian gave birth to a cub,Tai Shan,in 2005.
The pandas are on a 10-year loan from China and are scheduled to return in 2010.
The zoo's scientists have not decided whether to try again to breed Mei Xiang next year.