1. Department of General Surgery, The Second People's Hospital of Guangdong Province, Southern Medical University, Guangzhou, Guangdong 510317, P.R. China
2. Department of General Surgery, People's Hospital of Heyuan, Heyuan, Guangdong 517001, P.R. China
3. College of Animal Science and Technology, China Agricultural University, Beijing 10083, P.R. China