National Zoo officials not sure what killed panda cub

WASHINGTON — The giant panda cub that died over the weekend had liver irregularities and fluid in its abdomen, National Zoo officials said Monday, but it was unclear whether that contributed to its sudden demise.

The zoo’s chief veterinarian, Suzan Murray, said the cub’s heart and lungs appeared normal based on preliminary findings of a necropsy — equivalent to a human autopsy. Test results are expected within a week to help identify the cause of death.

Zookeepers referred to the cub as “she” during a news conference because it appeared to be female, but they won’t know conclusively until lab tests are completed.

A small amount of milk was found in the cub’s gastrointestinal tract, evidence that it had nursed, officials said. But because the tract was not full, veterinarians could not confirm how well it had nursed in its final hours.

Fluid in the abdomen is an “unusual finding” for a cub of such a small size, Murray said, but some free fluid in the abdomen would not be unusual in an adult giant panda.

The liver “felt a little hard in places,” she said, and the color was “not uniform.”

The miracle cub, born late on the night of Sept. 16, was conceived by artificial insemination after five failed pregnancies for Mei Xiang, the cub’s 14-year-old mother. In accordance with Chinese tradition, the cub was not going to be named until December, 100 days after its birth.

Panda cubs are born about the size of a stick of butter, and their mothers weigh 1,000 times more. It’s not uncommon for a mother to accidentally crush her cub, but zoo veterinarians ruled out that possibility in this case.

The giant panda is an endangered species and, some fear, on the brink of extinction. Only about 1,600 are believed to exist in the wild and a few hundred live in captivity.

The rare creatures are also fragile: The mortality rate for panda cubs in captivity is 26% for males and 20% for females during their first year of life.

Mei Xiang’s cub died at just under a week old. The cub made its last recorded sound about 9 a.m. Sunday, and zookeepers realized something was wrong at 9:17 a.m. when the mother made an unusual honking sound they interpreted as a distress call.

Zoo officials and panda fans grieved with her, even as they cautioned not to attribute human emotions to the panda. Mei Xiang has been cradling a toy similar to the way she cradled her cub — a clear sign, zoo Director Dennis Kelly said, that she has not stepped out of the mothering role.

But Kelly said he was “cautiously optimistic” that Mei Xiang would slowly return to her normal routine, adding that she’d already begun eating bamboo and biscuits.

The cub was the second in seven years for Mei Xiang and her male partner, Tian Tian. Their first, Tai Shan, was born in 2005 and became the zoo’s star before he was returned to China — as part of conditions for the pandas’ presence in the U.S. — in 2010.

The zoo had anticipated that the number of visitors would have increased by about half a million in the coming year as a result of the latest birth. Thousands had watched the panda and newborn cub on the zoo’s “panda-cam.”

Four American zoos have giant pandas, including San Diego, where a cub was born in July that seems to be doing well.

National Zoo officials said they had been in contact with their Chinese counterparts about the death.

“Collectively, their concern, our concern, is for Mei Xiang,” Kelly said. “Hopefully we will get a better understanding of giant panda reproduction and cub health.”

But that offered little consolation one day after the cub’s death.

“Every loss is hard,” Kelly said. “This one is especially devastating.”

danielle.ryan@latimes.com