The female panda cub who died last month at Washington's National Zoo did not have fully formed lungs, a necropsy on the young bear has found.
In a statement, the zoo said the 6-day-old cub's cause of death was insufficient oxygen to her liver.
The cub, a surprise for mother Mei Xiang, was born September 16, and her death just a week later was devastating to the Zoo's staff and the public, the Associated Press reported.
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The baby's mother and father Tian Tian have begun to return to normal. Mei Xiang was given a toy to cradle after the cub's death, but has stopped holding it and started to regain her appetite.
"We are happy to report that Mei is almost completely back to her old self! Her hormones have returned to normal levels, as has her behavior. Mei is choosing to go outside in the mornings. In the afternoons she can usually be found napping on her indoor rock work," the zoo said, USA Today reported.
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No decision has been made about plans for Mei Xiang and Tian Tian, who are on contract to remain at the National Zoo until December 5, 2015.
The zoo has not ruled out the possibility that Mei could become pregnant again.
"We're hopeful that she would be able to again in the future," the National Zoo's Veterinarian Suzan Murray said at a news conference, Reuters reported.
Both giant pandas remain on view at the Zoo's panda habitat.
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