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The National Zoo still doesn’t know why a 6-day-old panda cub died at the zoo yesterday, officials said at a press conference this morning.

While the panda, who was determined during the necropsy to be female, had extra fluid in its body and an abnormal liver, it’s not clear yet whether either issue was responsible for her death. Because the cub didn’t show any outward physical trauma, it’s unlikely that panda mother Mei Xiang accidentally crushed her cub as other pandas have, according to chief veterinarian Suzan Murray.

National zoo director Dennis Kelly said the zoo will examine differences between other zoos’ panda programs to see if it can learn how to better, but that he didn’t think the zoo’s panda fertilization program contributed to the cub’s death.

“Nothing suggests that in hindsight we would do anything differently,” Kelly said.

Mei Xiang’s behavior has changed since her cub’s death, according to Murray, although the panda is still eating and interacting with zoo staff.

“She will slowly return to normal, but we’re going to keep a watch on her,” Kelly said.

Photo via Flickr user hinnosaar used under a Creative Commons license