Effect of Swine Sire Line and Selection Index Category on Wean-to-Finish Growth Performance and Carcass Characteristics.

The objective of this study was to compare 3 sire lines and effect of selection index category within line on growth (6.1 ± 0.29 to 129.8 ± 2.16 kg BW) and carcass characteristics of commercial pigs. A randomized complete block design (blocking factor being day of start on test) was used with a 3 × 2 factorial arrangement of treatments: 1) Sire Line [L; Green (GL) vs. Blue (BL) vs. Yellow (YL)] and 2) Selection Index Category [IC; High (HIC) vs. Low (LIC)]. The lines were representative of ones widely used in the industry. The HIC and LIC sires were from the top 25% and at the mean line-specific index value, respectively. Ten sires from each IC from each line were mated to 15 crossbred dams; dam lines were equally represented across sires. Progeny (n = 2880) were housed in mixed-sex groups (barrows and gilts) of 32 pigs (15 replicates) at a floor space of 0.66 m² per pig. Pigs had ad libitum access to feed and water throughout the study. Pen was the experimental unit and data were analyzed using PROC MIXED of SAS; the model accounted for L, IC, 2-way interaction, block, and replicate. There were L × IC (P < 0.05) for most measurements. For ADG, there was no difference (P > 0.05) between HIC and LIC for the GL (0.76 vs. 0.77 kg, respectively) or the YL (0.76 vs. 0.76 kg, respectively), however, ADG was greater (P < 0.05) for HIC than LIC for BL (0.83 vs. 0.80 kg, respectively). For G:F, there was no difference (P > 0.05) between HIC and LIC for the GL (0.402 vs. 0.410 kg:kg, respectively) or for the BL (0.425 vs. 0.429 kg:kg, respectively), however, G:F was greater (P < 0.05) for HIC than LIC for YL (0.432 vs. 0.419 kg:kg, respectively). For carcass lean, there was no difference (P > 0.05) for HIC and LIC for the GL (53.34 vs. 53.51 %, respectively) or for the BL (53.44 vs. 53.30 %, respectively), however, carcass lean was greater (P < 0.05) for HIC than LIC for YL (54.71 vs. 54.18 %, respectively). These results show important differences in growth performance and carcass measurements between commercial sire lines and that the relative differences between sires with high and low selection index differs between sire lines which probably reflects differences in the weighting given to traits in each line-specific index.