Effect of selection for residual feed intake during the grow/finish phase of production on sow reproductive performance and lactation efficiency

As feed costs continue to rise and efficiency during finishing is emphasized, the impact of selecting for more efficient grow/finish pigs on reproductive performance and feed efficiency of sows must be evaluated. Therefore, the objectives of this study were to evaluate correlated responses for sow reproductive performance and lactation feed efficiency to selection for residual feed intake (RFI) during the grow/finish phase of production (RFIG/F) in 2 selection lines of pigs developed at Iowa State University (Ames, IA) and to estimate heritabilities of these traits. One line was selected over 7 generations for decreased RFIG/F (low RFI [LRFI] line) and the other line was randomly selected for 5 generations and then selected for increased RFIG/F (high RFI [HRFI] line). After 7 generations of selection, LRFI sows had 1.0 more piglets farrowed (P = 0.11) compared with HRFI sows, 1.3 more pigs born alive (P < 0.05), similar farrowing survival, 0.4 fewer mummies (P < 0.01), and more piglets weaned, both by litter (1.6 more; P < 0.01) and by sow (1.1 more; P < 0.01). Low RFI sows consumed 25 kg less feed and lost 9.8 kg more BW, 7.0 kg more fat mass, and 3.1 mm more backfat than HRFI sows (P < 0.001) during lactation. Although LRFI sows had a greater negative energy balance (-19.8 vs. -8.0 MJ ME/d; P < 0.001), they had better RFI during lactation (-28.6 vs. 8.2 kg; P < 0.0001), and the trend was for LRFI sows to have better lactation efficiency (61.3 vs. 57.8%; P = 0.47) than HRFI sows. Heritabilities for sow weights, sow body composition, sow maintenance requirements (estimated from BW), and piglet birth weight were high (h(2) > 0.4, SE < 0.07). Traits pertaining to piglet growth during lactation and mobilization of body tissue of the sow were moderately heritable (0.2 < h(2) < 0.4, SE < 0.07). In conclusion, selection for decreased RFIG/F has favorably affected piglet performance and lactation efficiency but has unfavorably affected sow body condition loss and energy balance during lactation. These results indicate that pigs selected for increased efficiency during grow-finish are better able to direct resources where needed during other life history phases, that is, reproduction and lactation.