1. Institute of Swine Science; Nanjing Agricultural University; Nanjing 210095 China
2. Department of Animal Science; North Carolina State University; Raleigh NC 27695 USA
3. Changzhou Jiaoxi Cooperatives of Erhualian pigs; Changzhou 213116 China
4. College of Animal Science and Veterinary Medicine; Jiangxi Agricultural University; Nanchang 330045 China