1. Institute of Animal Science, Jiangsu Academy of Agricultural Sciences, Nanjing, China
2. Department of Anatomy, Physiology, and Cell Biology, University of California Davis, Davis, CA,USA
3. Department of Animal Science, University of California Davis, Davis, CA, USA
4. School of Life Science and Technology, Inner Mongolia University of Science & Technology, Baotou, China
5. Department of Biology, University of Pennsylvania, Philadelphia, PA, USA