1. College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China
2. Sichuan Province General Station of Animal Husbandry, Chengdu 611130, China
3. Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada T6G 2P5
4. Department of Animal Science, Xichang College, Xichang 61500, China