Mei Xian entered her 48-hour annual heat Saturday, but failed in attempts to mate with Tian Tian. Both pandas then were sedated and sperm from Tian Tian injected into Mei Xian, The Washington Post reported Monday.
Mei Xian and Tian Tian were to be placed in separate enclosures so veterinarians could monitor Mei Xian to see if she is pregnant. A panda's gestation can range from three to six months.
Via artificial insemination, the panda couple produced one cub, Tai Shan, in 2005 but subsequent breeding attempts failed. Tai Shan is to be sent to China early next month under an arrangement with the Chinese government, which owns all giant pandas in U.S. zoos.
Mei Xian and Tian Tian are on a 10-year loan from China that expires this year. The zoo is negotiating for an extension, officials said.