Two developments have put in doubt the future of the successful panda breeding program at the San Diego Zoo.
Six pandas have been born at the zoo under a research agreement with the Chinese government. The pandas remain the property of the Chinese but, during their stay in San Diego, are among the zoo's most popular animals, including on its Internet "panda-cam."
Gao Gao, the giant panda male who has fathered five of the six cubs, was diagnosed with testicular cancer and underwent surgery Tuesday to remove his right testicle.
While there is no sign of cancer in his left testicle, his continuation as a stud has yet to be determined, zoo officials said.
Gao Gao, who was caught in the wild in China, is in his mid-20s, which is approaching old age for a panda. He also has a heart condition.
Also this week, researchers have concluded that Gao Gao's mate, Bai Yun, probably will "no longer go through a breeding cycle."
Researchers have been watching Bai Yun for changes in her estrous behavior to see whether she was prepared for breeding. The lack of those changes, they said, suggest that Bai Yun, who is 22, is approaching the panda equivalent of menopause.
Without the participation of Gao Gao and Bai Yun, the breeding program would be halted, officials said.
"No changes in the panda population at the zoo are currently expected," the zoo said in an official statement.
Discussions are expected this year between officials from San Diego Zoo Global and the Chinese government. The Chinese were informed of Gao Gao's diagnosis and consented to the surgery.
Bai Yun, who came to the zoo in 1996, is the mother of all six cubs born at the zoo.
Five of the cubs are the product of mating with Gao Gao. Her first cub, Hua Mei, born in 1999, was the product of artificial insemination.
Her first intended mate, Shi Shi, proved uninterested in mating. He was replaced in 2003 by the more lusty Gao Gao.
All but one of Bai Yun's cubs have been sent to China, under the loan agreement. Along with Bai Yun and Gao Gao, the zoo also has Xiao Liwu, who is 20 months old.