National Zoo officials said Sunday they do not believe there will be a pregnant panda this year at the animal park.
"It looks as though Tian Tian and Mei Xiang did not breed this year," said assistant Curator Lisa Stevens. According to zoo officials, the pair had tried to mate several times since Friday.
"Tian Tian gets an 'A' for effort, but I have to say he gets an 'F' for technical merit," said Stevens. "He did not make the connection we were all hoping for."
By late Sunday, zoo officials believed Mei Xiang was no longer in heat. Pandas only come into heat once a year, and the female is receptive to her male companion's advances for only two or three days.
This is the third year the 5-year-old female and 6-year-old male have tried to breed. A panda's prime breeding age is between 5-8 years old.
Stevens said if the panda pair are unsuccessful again next spring, the zoo will look at other fertility options, such as artificial insemination.
The last time the National Zoo had a pregnant panda was 1989. The zoo's previous panda pair -- Ling Ling and Hsing Hsing -- bred successfully four times and produced five cubs, but none lived longer than a few days.
The last panda birth in the United States was a male cub, born at the San Diego Zoo in August 2003. About 1,000 pandas live in the wild, and an additional 110 are in captivity, most of them in China.