GIANT PANDA BAI YUN TO RETURN TO PUBLIC EXHIBIT AT SAN DIEGO ZOO

Researchers, Keepers and Veterinarians Conclude Pregnancy Monitoring

     Female giant panda Bai Yun will return to the north panda exhibit at the San Diego Zoo starting Wednesday, August 31, 2011. The 20-year-old panda has been off exhibit since breeding with panda male Gao Gao in April. For the last 19 weeks, animal care staff monitored Bai Yun's behavior and hormone levels, performed regular ultrasounds and gathered thermal images. After careful analysis of these data, researchers from the San Diego Zoo Institute for Conservation Research have determined that Bai Yun is not pregnant. They will continue to study all the data collected from this monitoring to find new insight into the processes of giant panda pregnancy.

     While there are many elements of panda pregnancies that still are not understood, it is accepted that after breeding, a panda's fertilized egg remains suspended in her uterus until it is cued to implant. The precise nature of this implantation cue is still unknown to scientists. Giant pandas routinely delay the implantation of the embryo as much as two to three months. After implantation the fertilized egg begins to develop. Impending birth is predicted on the basis of ultrasound images, as well as behavioral, hormonal and anatomical changes documented by the panda team.

     During this year's pregnancy monitoring, researchers saw increases in Bai Yun's progesterone levels that were typical of past pregnancies, and behavioral changes - activity levels and suppression of appetite - were seen at levels that were typical of prior gestation periods. Through thermal imaging, researchers were also able to see activity in both the left and right uterine horn. However, the ultrasound images never revealed a fetus and the reasons that this birthing season didn't yield a cub are yet unknown.

     Bai Yun and Gao Gao's breeding introductions appeared normal in April, and Bai Yun's behavior and hormone levels have not initially indicated that age was a contributing factor to the results of this breeding season. Medical exams of Gao Gao also offer no obvious age-related issues that would prevent conception. Researchers also tracked the levels of Bai Yun's cortisol levels over the last four months. Elevated cortisol levels can sometimes indicate stress; however, there was no increase in Bai Yun's cortisol levels that would suggest she experienced undue stress. All of the test results show that Bai Yun is an aging, healthy panda potentially capable of breeding in the next few years.

     Bai Yun was born at the China Center for Research and Conservation of the Giant Panda in the Wolong Nature Reserve on Sept. 7, 1991. She was the first panda to be born and survive at that breeding center. Bai Yun, who's name means "white cloud" in Chinese, arrived at the San Diego Zoo in September 1996 on a research loan. Over the years, she has produced five healthy cubs.