A quantitative ethogram of aggressive and submissive behaviors in recently regrouped pigs

Twenty prepubertal Yorkshire X Hampshire pigs were mixed in groups of four. Their behaviors were recorded on video tape for 48 h, and a detailed behavioral analysis was performed. Aggressive interactions of 10 unique pairs of pigs were observed. Twenty-five distinct behavioral categories were identified in the total data set, which contained 1,846 behaviors. On average, an interacting pair showed 92 behavioral elements (range: 10 to 307). Eighty-one percent of the behaviors observed consisted of bites and pushes given and received. Bites were targeted mainly at the ears (55%), face (17%) and neck (23%). Most bites to the rump and turning the body 180 degrees occurred during the last third of the fight. Pigs that eventually won fights showed higher incidences of ear bites and lower incidences than expected of head-under-head pushing and body-turning. Pigs that lost fights showed higher frequencies of head-under-head pushing and body-turning. Losers also showed a lower frequency of rump biting. Overall, many of the behaviors performed by the losing pigs were followed by the loser receiving an ear bite. Body-turning was a sign of submission and was always preceded by, and often followed, ear-biting. Once a pig showed body-turning, it generally avoided further face-to-face interaction. Behaviors exhibited as signs of submission were found in each of the 10 pairs observed.