Growth Performance and Carcass Traits of Low and High Fiber Diet Selection Lines of Pigs Fed Either Low or High Fiber Diets

The objective of this study was to determine whether genetic selection of pigs when consuming high fiber diets could improve growth performance of subsequent generations of grower-finisher pigs fed diets high in fiber. Barrows (n=175; 45.8 ± 6.5 kg) were used in a 2x2 factorial RCBD with genetic line (selected high fiber and selected control lines) and diet (control or high fiber) as factors. Pigs were housed in pens (4 to 5 pigs/pen) with pen as experimental unit. Genetic lines were developed by selection for lean growth in pigs consuming high fiber or control diets for 3 generations. High fiber diets were formulated to include 45% fibrous byproducts (15% each of DDGS, soybean hulls, wheat middlings) and control diets were corn-soybean meal based. A 3-phase feeding program was used with diets formulated to contain equal SID lysine to net energy ratios between treatments within phase (control diet contained 0.93, 0.80, and 0.70% SID lysine and 2,484, 2,518, 2,537 kcal/kg NE for Phase 1, 2, and 3, respectively; high-fiber diet contained 0.82, 0.71, and 0.62% SID lysine and 2,187, 2,235 and 2,245 kcal/kg NE). Pigs were marketed by BW block with heavy pigs marketed on d 64 (BW=118±10.9 kg) and light pigs on d 78 (BW=118±10.8 kg). Feed disappearance and BW were recorded at the end of each phase, backfat (BF) and loin eye area (LEA) were measured using real-time ultrasound, and HCW was determined to calculate yield. Data were analyzed using PROC MIXED models with initial BW as a covariate. There were no interactions (P>0.11) between diet and genetic line. Genetic line had no effects on ADG, ADFI, Gain:Feed, or caloric efficiency (Gain:NE intake), but the selected high fiber line had decreased (P<0.05) carcass yield (71.7 vs. 72.6%). Pigs fed high fiber diet had lower (P<0.05) ADG for Phase 1, 2, and overall (9.3% lower), higher ADFI for Phase 3 (P=0.012), lower (P<0.05) Gain:Feed for Phase 2, 3, and overall (10.2% lower), increased (P<0.05) caloric efficiency for Phase 1 and 2, and reduced (P<0.05) HCW (81.4 vs. 88.8, kg), LEA (16.89 vs. 18.24 cm²), BF (1.66 vs. 1.98 cm), yield (70.8 vs. 73.5%) and daily lean gain (0.36 vs. 0.39 kg/d). Genetic selection for lean growth of pigs fed high fiber diets for 3 generations did not improve carcass traits or growth performance; however, feeding high fiber diets decreased growth performance, carcass characteristics, and daily lean gain in finishing pigs.