"We expected to get 10 cubs this year, but, as you can see, we were too conservative," Zhang was quoted as saying by the Xinhua News Agency.
26 of the surviving panda cubs were bred by zoologists in China's southwest province of Sichuan, with 17 born at the Wolong Giant Panda Protection and Research Centre and nine at the Chengdu Research Base, the report said.
The other surviving panda was born in the neighbouring Chongqing municipality, while a 28th was born to the panda Lun Lun at Atlanta zoo after being artificially inseminated with the help of Chengdu researchers.
Giant pandas, famous for their sexual inactivity, are among the world's most endangered animals.
China's forestry administration says that about 1,590 pandas are living in the wild, mainly in Sichuan and the province of Shaanxi.