Enormous strides have been made to improve feed efficiency during the grow-finish period by selecting for pigs that grow faster and that have less backfat. Recently, selection for feed efficiency has been accelerated by directly measuring feed intake and, therefore, feed efficiency on animals in nucleus breeding populations. The question whether selection for feed efficiency results in pigs that are less robust and that may be less able to cope with physiological and behavioral stress is, however, often raised. After all, mounting an immune response and coping with stress requires substantial amounts of energy, and pigs that are very efficient may not have the resources to mount an effective response to cope.