Effect of group composition on agonistic behavior and performance of newly mixed weaned pigs
The objective of the present study was to compare the differences and regularities in social behavior of newly mixed piglets under the conditions of large-scale commercial pig production. Three methods of grouping piglets at weaning (31-34d) into a 12-member weaned pool were studied: 6 pigs from 2 litters (6 × 2); 4 pigs from 3 litters (4 × 3); 3 pigs from 4 litters (3 × 4). Each method had three replicates and the weaned piglet body weight ranged from 7.4 up to 9.8 kg. Agonistic behavior was recorded over three observation periods: 0-1.5 h immediately after mixing; 1 h, 4-5 h later the same afternoon; 5 days later for 1 h. Both contact (head thrusting, biting and pushing) and non-contact (chasing, threatening and displacement) agonistic behavior were recorded. Contact behaviors made the most significant contribution to obtain a new dominance status in the social hierarchy and decreased significantly in frequency over time. Subsequently, the rate of non-contact behavior also declined. During the first observation period covering the crucial time for establishing dominance hierarchy, structure 4 × 3 had significantly less head thrust than 6 × 2 or 3 × 4. Generally, 4 × 3 showed a lower rate of contact behavior compared to the other two groups as well as less non-contact behavior than 3 × 4, but it was similar to 6 × 2. It appears that the 4 × 3 structure may cause less physical encounters than the other two groupings.
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