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Breeding organizations are continuously adapting their breeding goals to support the needs of farmers and society. There is a world-wide demand for better feed efficiency due to the competition for land between food and feed production, but there is also more attention on some of the undesirable correlated responses such as increase in disease susceptibility, and more observed mal-behaviour such as aggression and tail biting.
A very promising selection method with the potential to improve both animal welfare and economic output is the use of social genetic effects (SGEs) in breeding programs. A social genetic effect is a heritable effect of one individual on the trait value of another individual. The breeding approach using SGEs incorporates both the direct genetic effect due to the focal individual, and the genetic effect an animal has on its pen mates into the trait value of the focal individual. While traditional methods focused on individual performance only, this strategy could improve growth in pigs, as well as the behaviour of pigs which are housed in groups. A one generation selection experiment where pigs (gilts and castrates) were grouped based on a high or low SGE for growth was conducted to investigate underlying behavioural differences and confirm previous results (N = 480).
Aggression measured by skin lesions and fighting during regrouping did not differ between high and low SGE pigs. However, pigs with a high SGE showed less aggression after reunion with familiar pigs and also had less non-reciprocal biting in the week after regrouping. During the finishing phase, high SGE pigs showed systematically less biting behaviour; 40% less aggressive biting and 27% less oral manipulation of pen mates. High SGE pigs were also chewing 40% less on distraction material and consumed 30% less of the jute sacks provided. These differences were also expressed in the tail damage, where high SGE pigs had a better tail score (less damage) compared to low SGE pigs. One remark on this one-generation selection experiment should be made. The contrast on growth, by selecting sires and dams with high and low SGEs, did not result in significant differences in growth in their offspring. The authors argue that control measures (jute sacks, sawdust) to limit harmful behaviour might have reduced the expression on SGEs on growth and that research under commercial circumstances needs to be conducted.
While traditional methods focused on individual performance only, the SGE strategy could improve growth in pigs, as well as the behaviour of pigs which are housed in groups. Social genetic effects offer the opportunity to breed for improved behaviour while maintaining performance.
Naomi Duijvesteijn, John. M. Eggert. The prospects of selection for social genetic effects to improve welfare and productivity in pigs. Proceedings of the 47th AASV Anual Meeting.
