Table 2.
Action units (AUs) and ear action descriptors (EADs) selected by the co-occurrence method. Pain intensity levels were defined based on movement asymmetry. Not all horses experienced both levels of pain intensity, why the number of horses (n) experiencing each intensity level is stated in brackets. The frequency of co-occurring AUs and ADs in ‘no pain’ video sequences was compared to the frequency in ‘mild pain intensity’ sequences (0–1) and ‘moderate pain intensity’ sequences (0–2). The frequency of co-occurring AUs and ADs in ‘mild pain intensity’ sequences was also compared to the frequency in ‘moderate pain intensity’ sequences (1–2). The observation window size (OWS) was set to 2 s. p-values are shown in brackets (paired t-test) and differences were considered significant at p < 0.05.
| EquiFACS code | Level of pain intensity | ||
|---|---|---|---|
| 0–1 (n = 7) | 0–2 (n = 5) | 1–2 (n = 4) | |
| Ears | |||
| Single ear forward (SEAD101) |
✓ (p < 0.001) |
||
| Single ear rotator (SEAD104) |
✓ (p < 0.001) |
✓ (p < 0.001) |
|
| Upper face | |||
| Blink (AU145) |
✓ (p < 0.001) |
||
| Half blink (AU47) |
✓ (p < 0.001) |
✓ (p < 0.001) |
✓ (p < 0.001) |
| Lower face | |||
| Upper lip raiser (AU10) |
✓ (p = 0.210) |
||
| Lower lip depressor (AU16) |
✓ (p = 0.241) |
||
| Lips part (AU25) |
✓ (p = 0.753) |
||