Table 1. Information on the layer farms of different scale in the main egg production area in northern China evaluated in this study.
| Province | Farm1 | Scale | Layer strain2 | Housing system | Structure |
|---|---|---|---|---|---|
| Shandong | A | 30,000 | Hy-Line Brown | Semi-open | |
| B | 50,000 | Hy-Line Brown | Semi-open | ||
| Liaoning | C | 19,000 | Hy-Line Brown | Semi-open | |
| D | 60,000 | Hy-Line Brown | Battery cage | Semi open | |
| Henan | E | 40,000 | CAU-3 | Semi-open | |
| F | 250,000 | CAU-3 | Closed | ||
| Hebei | G | 4,000 | Hy-Line Sonia | Open | |
| H | 100,000 | Hy-Line Brown | Closed |
1
Farms were named alphabetically;
2
Same chicken breed was kept in each laying house