Sorting means mixing pigs into pens according to size and is commonly used to maximize use of barn space when feeder pigs are brought into a grower-finisher barn. Although most producers find that sorting newly-weaned pigs has little effect on productivity, sorting grower-finisher pigs can reduce gains. This is most evident if regrouping is done late in the grower period. The reason large pigs gain more slowly after sorting has been attributed to disruption of the social status within the pen. In a newly-grouped pen, aggressive, dominant pigs may interfere with feeding and drinking by subordinates. This reduces overall pen gain.