Ethological investigations on the perpetrators and victims of tail biting in weaner pigs

Abstract Tail biting in pigs with undocked tail often occurs in a high frequency and then leads to significant injuries. In previous investigations tail lesions were recorded. In direct visual observations of 98 weaner pigs in 9 pens and in two rounds, the frequency of mutual bellynosing and biting (including tail biting) was registered, perpetrators and victims were identified, and sociometric parameters (percentage of one-way and two-way relationships) analyzed. Based on all mutual manipulations, tail biting accounted for 11.1%. Much more frequently mutual bellynosing (59.6%) and biting into other parts of the body (29.3%) occurred. The number of unknown dyads (= pairs) that had never interacted during the observational period was low and zero in two out of nine groups. In these groups, all animals ("each with each other") were involved in mutual interactions (including tail biting) as perpetrator and / or victim. In the other seven groups between 80.3 and 98.2% of all couples were involved. The percentage of two-way relationships (up to 81%) shows that a large number of dyads performed mutual interactions. There was a positive correlation between the number of actions (r = 0.32) and the percentage of two-way relationships (r = 0.53) and the percentage of partial or total tail loss at the end of rearing. Even with a diverse range of options for enrichment, a high frequency of tail losses (67%) at the end of rearing could not be prevented.