1. College of Animal Science and Veterinary Medicine, Shanxi Agricultural University, Shanxi, People's Republic of China.
2. Centre of Experiment Teaching, Shanxi Agricultural University, Shanxi, People's Republic of China.
3. College of Life Science, Shanxi Agricultural University, Shanxi, People's Republic of China.
4. State Key Laboratory for Agrobiotechnology, College of Biological Science, China Agricultural University, Beijing, People's Republic of China.