A DIFFERENCE IN WEIGHT REDUCES FIGHTING WHEN UNACQUAINTED NEWLY WEANED PIGS FIRST MEET

Abstract

The mixing of weaned pigs from different litters was observed so that the effect of a large difference in bodyweight on fighting could be examined. When 5- to 6-wk-old pigs met in pairs for 1 h, fights were longer and biting more frequent if the difference in weight between the pigs was small (< 0.5 kg) than if it was large (> 3.0 kg). In groups of four 5- to 6-wk-old pigs taken from different litters, fighting was more prolonged during 2 h after mixing if there was little weight variation in the group (coefficient of variation [Formula: see text]) than if there was large weight variation (coefficient of variation [Formula: see text]). When groups of four pigs were formed by taking one large and one small pig from each of two litters, the longest duration of fighting occurred between the two large pigs. Significantly less fighting occurred between the large and small pigs and between the two smaller pigs. Subordinate pigs were less likely to retaliate against the dominant pigs if the weight difference was large. It seemed that the presence of large pigs in the group inhibited fighting between equally matched smaller pigs. I suggest the common procedure of mixing pigs matched for weight exacerbates the initial fighting but how this affects growth rate will depend on the level of competition over food. Key words: Pigs, aggressive behavior, weight variation, mixing