The efficiency of pig production can theoretically be increased by combining the two productive functions, growth and reproduction in the same animal. This is the underlying principle of the once-bred gilt. The production of once-bred gilts also serves to solve another problem, which is the difficulty of providing adequate welfare for the sow over several parities. These problems arise because the Increasingly diverse size of sows as they mature, results in fighting, particularly when sows are mixed after completing the lactation. Similar reasons also virtually necessitate individual feeding.throughout pregnancy To overcome these problems, it is widespread practice to confine sows very closely in individual stalls or farrowing pens for several years, a practice which has rightly attracted some criticism.