Social interactions between pigs can originate from heritable traits and are then referred to as indirect genetic effects (IGE), meaning that a pig can influence the trait value of a pen mate genetically. The aim of this thesis was to investigate the contribution of IGE to breeding goal traits in pig breeding programs. This was investigated by incorporating IGE in mixed models containing random effects, or by using genomic information to detect associations between the phenotype and the direct and indirect genetic effects of the focal pig and its group mates.
A region on chromosome 6 was significantly associated with the direct effect on androstenone. Several candidate genes were identified which are involved in the synthesis and metabolism of androgens. SNPs on chromosome 9 and 14 were significantly associated with the indirect effect on androstenone, but no clear candidate genes could be identified. Besides associations between phenotype and genotype, also a methodology to model SNPs for indirect genetic effects was presented.Also a validation study was performed to quantify the added value of IGE for growth in pigs. No significant improvement was observed in ability to predict observed phenotypes between a classical animal model and a model including IGE. The structure and size of the dataset for a large part influenced the outcome of the validation. Therefore we cannot confirm or reject the added value of IGE.