When scientists and veterinarians determined that the two had not mated, Tang Chunxiang -- the assistant director and chief veterinarian of the China Conservation and Research Center for the Giant Panda at the Wolong Nature Reserve, Sichuan Province, China -- artificially inseminated Mei Xiang Saturday morning using both fresh and frozen sperm from Tian Tian.
Female giant pandas are only fertile for a few days every year, so when officials at the zoo noticed elevated estrogen levels in Mei Xiang Tuesday, they knew it they had little time.
"We are hopeful that our breeding efforts will be successful this year, and we're encouraged by all the behaviors and hormonal data we've seen so far," said Dave Wildt, head of the Center for Species Survival at the Smithsonian Conservation Biology Institute. "We have an extremely small window of opportunity to perform the procedures, which is why we monitor behavior and hormones so closely."
Mei Xiang, 15, and Tian Tian, 16, are on loan at the Smithsonian National Zoo from China until 2015.
Giant pandas are an endangered species, with an estimated population of 1,600 worldwide.
Notable deaths of 2014 [PHOTOS]