EFFECTS OF STRAW AND UNFAMILIARITY ON FIGHTING BETWEEN NEWLY MIXED GROWING PIGS

Twelve pens each of 15 Large-White X Landrace pigs, weighing 25-30 kg, were formed by mixing two, three or four groups of unfamiliar pigs. These corresponded to the following mixing patterns: G2, seven and eight pigs; G3, five, five and five pigs; G4, seven and eight pigs. Each pig thus had an average of 7.5, 10.0 and 11.2 pigs in the same pen with which it was unfamiliar, respectively. For each mixing pattern, two pens were provided with straw and two were not. The pens were observed using video recordings for 5 days after mixing. The number of fights was unaffected by the presence of straw but increased (P < 0.01) with the number of unfamiliar pigs. For G2, G3 and G4, the average number of fights per pig was 2.7, 4.3 and 5.0, respectively, which equated to 36%, 43% and 45% of the number of pigs with which each pig was unfamiliar. The average length of fight (mean 98 s, median 48 s) was unaffected by mixing pattern or straw. However, fights were approximately 35% longer on Days 1-2 than on Days 3-5 (median 52 s vs. 39 s), largely because of a greater proportion of very long fights. The distribution of fights on Days 1-5 was 63.6%, 22.2%, 8.6%, 4.4% and 1.1% and was unaffected by mixing pattern or straw. G3 showed more activity and less feeding and drinking than G2 and G4 (P < 0.05). Activity decreased over Days 1-5 (P < 0.05) and was higher for pens with straw (P < 0.05). Fighting between newly mixed growing pigs was not reduced by straw bedding and increased with the number of pigs which were unfamiliar with each other.