Influence of origin litter on social rank, agonistic behaviour and growth performance of piglets after weaning

In pig production, mixing of piglets after weaning is a common management practice often leading to severe fighting aimed at establishing a social hierarchy. The intention of our study was to investigate whether social rank of piglets obtained by fighting within 3 days after weaning and mixing was affected by origin litter. We studied a total of 15 groups containing 180 piglets originating from 30 litters in two different experimental parts on two conventional pig farms. Each group was composed of six piglets each from two different litters, thus one group consisted of a total of 12 animals. Agonistic behaviour was analysed continuously during 72 h after weaning. Sociometric measures determining the linearity of the established social hierarchy as well as an individual rank index were calculated. Piglets were weighed the day before weaning and at the beginning of the fattening period. Piglets in groups of 12 established semi-linear hierarchies allowing the assignment of individual piglets to definite rank positions. There was a clear relationship between origin litter and dominance status. In almost all groups, littermates (LM) originating from one litter obtained higher rank indices than their non-littermates (non-LM) originating from the other litter within the same group (p < 0.05). High ranking animals tended to perform more attacks than lower ranking piglets and fought more, especially against non-littermates. There were no differences in daily weight gain between piglets of different rank positions or different litters during the entire rearing period. Our results indicate the existence of a litter-associated dominance when mixing piglets from two different litters after weaning, without any influence on daily weight gain, provided that piglets are fed ad libitum with a close animal feeding:place ratio (1.5:1).