The National Zoo announced Saturday that it had artificially inseminated the zoo's giant panda Mei Xiang after natural breeding failed to occur.

A team of veterinarians and scientists performed the insemination on Saturday morning.

Scientists said they determined Mei Xiang was ready to breed on March 26 after observing her urinary estrogen levels, which had begun to rise.

She was inseminated with a combination of fresh and frozen semen from the zoo's male panda, Tian Tian.

"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."

The decision to artificially inseminate occurred after scientists and veterinarians determined no natural breeding had happened overnight.

Tian Tian and Mei Xiang have one surviving offspring together, Tai Shan, who was born in 2005 and now lives in China. Mei Xiang gave birth to a female cub in September of last year, but she died one week later due to lung and liver damage. Both cubs were born as a result of artificial insemination.

The panda exhibit at the zoo will reopen today after being closed since March 26. Tang Chunxiang, the assistant director and the chief veterinarian of the China Conservation and Research Center for the Giant Panda at Wolong, helped perform the artificial insemination.

The height of panda mating season is between March and April, and pandas are pregnant for about 95 to 160 days, according to the Zoo. Pandas are only fertile for about 24 to 36 hours. Researchers say it's extremely hard for pandas to produce offspring in captivity, partially because of the short fertility window and partially because of a general lack of aggressive interest in mating on the part of male pandas -- a which is not a problem among wild pandas.

It's also hard to determine whether a female panda is actually pregnant because panda fetuses are so small.

Scientists will continue to monitor Mei Xiang's condition.