In static systems, producers move groups of sows into pens at the same time. Farmers group the animals by projected farrowing dates and keep the herd intact (except for drop-outs) during gestation. Producers do not add new sows to the original groups.

This system makes it easier for farmers to manage the gestation barn. It also allows sows easier access to the feed stations.

Static groups are better for sow welfare and produce lower levels of aggression than dynamic groups, advocates of such systems say. Avoiding the introduction of new sows enables the group to create a stable social structure (dominance hierarchy) more quickly. Since static groups are smaller than dynamic ones, aggression is reduced.

Hansen prefers static grouping systems. They are based on weekly breeding groups and are easier to manage. Producers with these systems do not need automatic separation facilities on the electronic...