It’s well-known there is a social hierarchy in pig groups. When these group dynamics change, during weaning, movement from building to building, or as groups are comingled, some pigs can act abnormally such as tail-biting.
The challenge is that tail-biting is sporadic. To understand how to manage these behaviors, researchers at the University of Minnesota, focused on the social network analysis method of studying social structures in pig groups and individuals.
Researchers created six pens of four-week-old pigs, with eight pigs per pen, to study for 6 weeks. Video recordings were scanned at 10 minute intervals to register pigs lying together or not.
Pigs were grouped according to their relatedness:
1. Littermates: All eight pigs (four barrows and four gilts) in a pen were related, farrowed and nursed by the same sow.
2. Non-littermates: All eight pigs in a pen (four barrows and four gilts) were farrowed and raised by eight different sows and were mixed when entering the nursery barn.
3. Half-group of littermates: One pen of two groups of littermates. Four pigs, two barrows and two gilts, came from each of two litters and were mixed when entering the nursery barn.
All pigs had no tail damage upon entering the study. An effort was made to achieve similar average weight and in-pen weight variation across all pens.
Results show the littermates were less socially connected in a pen, spending less time lying together with their pen-mates than non-littermates. Littermates had a higher incidence of tail-biting than non-littermates, with 15% of littermates recorded as being a victim of tailbiting. No pigs in the other treatment groups were recorded as tail-bitten.
Researchers say less social connection with pen-mates might predispose littermate pigs to developing tail-biting behavior.