EU pig welfare legislation required European pig farmers to shift from individual to group housing of pregnant sows by 1 January 2013. This requirement was principally designed to meet the sows’ needs for locomotion and interaction with conspecifics. This article explores how the legislation affected everyday sow–farmer interactions, which influence farm animal welfare to an important degree. We start by analysing conceptualisations of sow welfare and sow–farmer relations as implicated in the EU directive and the scientific advice that informed it. Contending that these conceptualisations largely overlook co-developments in sow housing systems and sow–farmer relations, we subsequently introduce an alternative analytical framework that builds on sociological, practice-oriented theories. We then apply this framework to analyse 19 qualitative interviews with pig farmers in Belgium on the on-farm introduction of group sow housing. In this analysis, we discern different ways in which farmers’ choices for particular group housing systems were co-constituted by and co-constitutive of everyday sow–farmer relations.We conclude by reflecting on the scientific and policy implications of these findings.