EFFECT OF SELECTION ON FEED UTILIZATION AND CARCASS SCORE EN SWINE

Abstract

Selection for feed utilization (FU) and carcass score (CS) based on full sib performance was practiced within three lines of Yorkshire pigs during ten generations. Line 1 was selected solely for FU, line 2 for CS and line 3 for the two traits combined in an index. Line 2 served as a control for lines 1 and 3 in FU and line 1 as a control for lines 2 and 3 in CS. Feed utilization was expressed as the amount of feed required per kilogram body weight gain. Carcass score was based on length, backfat thickness, loin eye area and belly grade measured on pigs marketed at 90 kg liveweight. Selection differentials for FU averaged 0.198 and 0.208 kg per generation for lines 1 and 3, respectively, while CS differentials were 7.2 and 7.4 points per generation for lines 2 and 3, respectively. Heritability estimates based on full sib performance and converted to individual bases were 0.16 for FU and 0.43 for CS. The phenotypic correlation between the two traits was −0.25 and the genetic correlation −0.55. Responses to selection for FU were 0.09 and 0.24 kg per generation for lines 1 and 3, respectively, while for CS they were 0.77 and 0.97 points for lines 2 and 3, respectively. Compared with the parental means, this represented a genetic improvement of 0.25 and 0.66% per generation for FU in lines 1 and 3, and 1.06 and 1.33% per generation for CS in lines 2 and 3, respectively. The realized responses in lines 1 and 3 to selection for FU Were 58 and 148% of the expectation, and 58 and 72% for lines 2 and 3 in CS. Due to larger selection differentials in line 3, along with a strong positive genetic correlation between the two traits observed in this particular population, selection for the combined traits was 1.35 and 1.10% more effective in improving FU and CS, respectively, than selection for these traits individually.