Managing aggression is important to the success of gestating sows in pens. This study was designed to examine different ways of mixing sows into a large dynamic pen equipped with electronic sow feeders.  Increased weight loss, lameness, and skin lesions were observed after introduction of sows to pen gestation, but these measures did not negatively impact sow productivity.  Aggression was minimal immediately following introduction.  Different strategies for mixing sows into the pen did not affect study outcomes.  The findings highlight the ability of a well-managed pen gestation system to achieve or exceed standard levels of productivity.   This results in part from the successful management of inter-animal aggression at the time of mixing.  Although weight loss, lameness and skin lesions increased after sows were entered in to the pen, these changes were sufficiently small as not to have meaningful long term biological and or productivity impact.   The minimum negative impact on sow productivity and health measures following introduction to this pen gestation system likely explains the lack of treatment effects as unwanted effects of aggression were prevented or minimized across all animals.