Pigs' skin lesions at weaning are primarily caused by standoff and being bullied instead of unilateral active attack at the individual level.

To evaluate the relationship between skin lesion scores and aggressive behavior categories (unilateral active attack, standoff, and being bullied) of individual pigs when placed into pens after weaning, duration and frequency of three aggressive behavior categories were observed from video. Behavior of 500 weaned pigs was recorded and observed during the first 48 h after mixing. The skin lesion scores at 24 h before mixing and at 2, 24, and 48 h after mixing was assessed. Canonical correlations and generalized linear mixed models analyses between three aggressive behavior categories and skin lesion scores were performed. The score of skin lesion on the front body was significantly greater (P < 0.05) than those on the middle and rear body at 2, 24, and 48 h after mixing. These behavior categories and skin lesion scores of weaned pigs reached the maximum at 2 h after mixing and then decreased gradually. Skin lesion score on the front of the body at 2 and 24 h were associated with CSS (comprehensive standoff score), and CBS (comprehensive being bullied score). The skin lesion score on front body at 2 h after mixing were positively associated with CBS and CSS during the first (P < 0.01) and the second (P < 0.01) hour after mixing. After mixing the skin lesion score on the front body at 2 h was positively associated with CAS (comprehensive unilateral active attack score) at the first hour (P < 0.01), but not at the second hour after mixing. The skin lesion score on the front body at 24 h were positively associated with CBS at the first 12 h and at the second 12 h (from 13 to 24 h) after mixing (P < 0.01). CAS was negatively associated with the skin lesion score on front body at the first 12 h after mixing, and negatively associated at the second 12 h after mixing (P < 0.05). In conclusion, skin lesion score of weaned pigs was the greatest on the front body at 2 h after mixing. The skin lesion score on front body at 24 h after mixing was positively associated with behavior of standoff and being bullied, but not unilateral active attack. These results suggest that the severity of skin lesions is not primarily caused by unilateral active aggressive behavior of weaned pigs after mixing at the individual pig level. [Display omitted] [ABSTRACT FROM AUTHOR]