1. Key Laboratory of Animal Genetics, Breeding and Reproduction of Shaanxi Province, College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, China;
2. Shandong Key Lab of Animal Disease Control and Breeding, Institute of Animal Science and Veterinary Medicine, Shandong Academy of Agricultural Sciences, Jinan, China;
3. College of Life Sciences, Shandong Normal University, Jinan, China;
4. Shandong Liaocheng Luxi Blackhead Sheep Farm, Liaocheng, Shandong, China