Under normal farming practices, piglets from different litters are often mixed around the time of weaning, and a high incidence of fighting and minor injuries often occur. The aim of this experiment was to determine the effect of age on the incidence of fighting in piglets mixed before weaning, at different ages between 5 and 26 days. We found no significant relationship between age and the likelihood that a pair of piglets would fight during the first 75 min after mixing. However, the duration of the first fight observed increased from 101±38 s at 5 days to 621±278 s at 26 days, mainly because of higher levels of unretaliated harassment and resting during the bouts. Younger pigs also showed 80% fewer injuries from the fighting. The results suggest some potential welfare advantage to allowing litters to mix at younger ages.
Pitts, A. D., Weary, D. M., Pajor, E. A., & Fraser, D. (2000). Mixing at young ages reduces fighting in unacquainted domestic pigs. Applied Animal Behaviour Science, 68(3), 191-197.