“Pigs selected on indirect genetic effects for growth display less biting behaviour,” concluded Irene Camerlink after researching Indirect Genetic Effects. The Wageningen UR researcher also has sound advice to pig farmers who want to reduce biting behaviour, such as tail biting, faster: “environment enrichment”.
Indirect Genetic Effects (IGEs) are the heritable effects that an individual has on the phenotype of its social partners. Selection for IGEs has been proposed as a method to reduce harmful behaviours, particularly aggression. However, the mechanisms behind IGEshave rarely been studied, clarifies Wageningen UR researcher Irene Camerlink. 'Our objective was to assess behaviour in pigs that were divergently selected for IGEs on growth (IGEg).'
In a single generation selection experiment, Irene studied 480 offspring of pigs that had been selected for relatively high or low IGEg (to broaden the contrast) and housed in homogeneous IGEg groups in either barren (conventional) or environments enriched with sawdust and straw. All kinds of behaviours were recorded. The two distinct IGEg groups did not differ in most behaviours, but did show less biting behaviour.
Less biting, tail damage and aggression
Pigs selected for having a positive effect on the growth of their group members performed less unilateral aggressive biting and showed considerably less aggression upon reunion with familiar group members after 24 h separation for a regrouping test. They displayed less ear biting of pen mates and less biting of objects provided in the environment. Pigs with a high IGEg had less tail damage, suggesting a reduction in tail biting. This is good news for farmers who want to reduce biting behaviour in pigs and for breeding organisations as this helps improve accurate registration of breeding values.
Another clear conclusion from this research was the positive effect of the enriched environment, e.g. inclusion of straw in the housing. 'Pigs kept in enriched housing conditions showed considerably less tail damage', according to Irene. Changes in biting behaviour between pigs selected for IGEg were not influenced by G×E interactions with regard to the level of environmental enrichment. It is likely that selection on IGEg targets a behavioural strategy, rather than any single behavioural trait such as aggressiveness.