09/24/2012 at 12:00 PM EDT
A day after the National Zoo's giant panda cub was found dead
inside the den she shared with her mother, a definitive cause of death remains unknown.
However, zoo veterinarians detected some fluid in her abdomen and a slightly abnormal liver, according to a statement posted on the zoo's official website
Monday. "They don't know yet whether either of those things is significant," the statement reads, "and they're still investigating."
But those were the only issues vets found during the necropsy (animal autopsy) of the estimated 4-oz. cub, who appeared to be female. There were no signs of external or internal trauma, so they know she wasn't crushed by mom Mei Xiang. Her heart and lungs also seemed healthy, so she did not suffocate. They saw traces of milk in her gastrointestinal tracks, so they know she was nursed by her mother before her death.
"We're still reeling from the loss of our giant panda cub," the statement continues. "We feel like the whole world is mourning with us."
Meanwhile, zookeepers continue to focus on the animal at the heart of the heartbreak: mother Mei Xiang. She seemed to sleep well Sunday night, according to the statement. Those monitoring her watched her cradle an object, which is believed to be an expression of her maternal instincts that she also showed before birthing her cub last Sunday.
At 217 lbs., Mei Xiang is smaller than her usual weight, which is normal for a recent mother, according to the statement. Still, she ate and drank some water Monday morning. If test results come back healthy, staff will once again give her access to her outside yard, if she chooses to use it.
For now, the zoo is concentrating on her well-being – not her future offspring. The cub's arrival, after all, came with a wave of optimism following hopeful speculation that finally, after seven years
, Mei Xiang would be a mother again. The zoo's chief veterinarian Suzan Murray described her as "the poster child for the perfect panda mom."
"We fully anticipate that she'll return to her normal wonderful giant panda self in a relatively short amount of time," the statement reads. "We will learn from this tragedy and hope we will gain a better understanding of the giant panda reproduction and cub health as a result."