The Chengdu Panda Base officially “retired” 23 year old hero mother Ya Ya at the end of 2012. From 1997 to 2010, she delivered thirteen cubs and twelve of them survived. Ya Ya became a surrogate mother to all the cubs born at the Chengdu Panda Base in 2010. In addition to her own cub Ya Yun, Ya Ya took care of six others after they were separated from their mothers. She was an incredibly gifted mother and base staff recognized that she could teach the youngsters lessons on how to be pandas.
Source: http://www.panda.org.cn/cn/news/news/2013-02-04/938.html