Breeding expert Li Xin checks the temperature of a cub at the Siberian Tiger Park in Harbin, Heilongjiang province. ZHENG XUEFENG/FOR CHINA DAILY The Harbin park is one of three run by the China Hengdaohezi Feline Breeding Center, the world's largest such facility for these rare tigers. During more than 30 years of research, the center has explored a complete …