1. Dairy Cattle Research Center; Shandong Academy of Agricultural Sciences; No. 159 North of Industry Road Jinan, Shandong 250131 China
2. National Center for Preservation and Utilization of Genetic Resources of Domestic Animals; National Animal Husbandry Service; Beijing 100193 China
3. Department of Animal Science; Iowa State University; 2361 Kildee Hall, 806 Stange Road Ames IA 50010 USA
4. Engineering Center of Animal Breeding and Reproduction; Jinan Shandong 250100 China