Objectives and strategies in pig improvement: an applied perspective.

Largely because of the influence of Charles Smith, simple performance testing of pigs over the previous 30 yr has been highly successful. With larger production units, current genetic objectives can be divided into two components: 1) to raise genetic potential for production traits and 2) to maximize the probability that this potential can be realized in practice. Faster improvement through increased accuracy and a more flexible nucleus structure are offered by BLUP methodology. Electronic measures of feed intake permit selection based on feeding behavior and the shape of the feed intake curve. After the elimination of the halothane gene, the next limiting factor for meat quality could be intramuscular fat. With more than 1500 mapped genes, the main constraints on marker-assisted selection are the high costs of DNA testing and the relatively small effects of this selection on performance. A combination of the possible effects of BLUP, the Meishan breed, and the ESR gene could give genetic improvements totaling 4 liveborn piglets per litter over the next 10 yr. There appear to be no limits on future improvement of lean growth, but risks are adverse changes in reproduction and disease resistance. Existing quantitative methods of improvement are very cost effective. The greatest challenge for molecular technologies may be the genetics of the immune system.