| Year\Traits | Farrrowing cycles | Culling ratio (%) |
|---|---|---|
| Mean ± S.D | Mean ± S.D | |
| 1970 | - | - |
| 1980 | 2.01 ± 0.21 | - |
| 1990 | 1.98 ± 0.32 | 30.45 ± 2.42 |
| 2000 (A) | 2.10 ± 0.22 | 28.31 ± 1.25 |
| 2010 | 2.20 ± 0.45 | 27.50 ± 1.45 |
| 2018 (B) | 2.30 ± 0.54 | 26.72 ± 1.76 |
| Average | 2.09 ± 0.29 | 28.25 ± 1.72 |
| B/A (%) | 9.52 | —5.62 |