Pork quality characteristics of loins from pigs divergently selected for residual feed intake on high or low energy diets

Abstract Text: The objective was to determine the effect of feeding a high energy, low fiber (HELF) or a low energy, high fiber (LEHF) diet on pork quality of loins from pigs divergently selected for residual feed intake (RFI). RFI is the difference in observed and expected feed intake of an animal given growth and backfat. The low RFI (LRFI) line is generally more efficient than the divergently selected high RFI (HRFI) line. Pigs (LRFI [80 barrows,75 gilts], HRFI [76 barrows, 77 gilts]) from generations 8 and 9 of the ISU RFI selection project were randomly assigned to 12 mixed line and sex pens per generation. Each generation, 6 pens were placed on the HELF diet (3.32 Mcal ME/kg; 9.5% NDF) and 6 pens onto the LEHF diet (2.87 Mcal ME/kg; 25.9% NDF). Pigs were slaughtered at mean BW of 122.5±8.0 kg (generation 8) and 128.4±8.0 kg (generation 9). Boneless loins were removed 24 h postmortem. Day 2 postmortem, chops were cut 2.54 cm thick. Ultimate pH was determined 48 h postmortem. One chop was homogenized 2 d postmortem for proximate analysis. Lean color was determined using a Hunter Labscan XE with a D75 light source and 1.27 cm aperture. Color, marbling and firmness scores were assigned at 2 d postmortem. Drip loss was determined 3 d postmortem as [(initial weight-final weight)/initial weight]x100. Data were analyzed using the mixed procedure of SAS with fixed effects of line, diet, sex, generation, and line*diet; random effects of slaughter group, pen, litter, and sire; and covariate of live weight. Percent moisture (P<0.01; 73.3% v. 73.7%) was higher, and drip loss (P<0.01; 1.60% v. 1.34%), color score (P<0.01; 2.3 v. 2.0), a* (P<0.01; 3.46 v. 2.64), b* (P<0.01; 11.28 v.10.73), marbling score (P<0.05; 1.4 v. 1.3), and percent lipid (P<0.01; 1.70% v. 1.30%) were lower in chops from LRFI pigs than HRFI.  Pigs fed the HELF diet had loins with greater L* (P<0.05; 51.53 v. 50.78) and lower percent moisture (P<0.01; 73.3% v. 73.7%) than loins from pigs fed the LEHF diet. Chops from LRFI pigs fed the LEHF diet had the lowest firmness scores (P<0.05).  Selection for LRFI impacted percent lipid and color score, although unlikely to be detected by consumers.  Diet affected lines in the same manner; loins from animals fed the HELF diet were more pale in color and had less percent moisture. USDA-AFRI Grant #2011-68004-30336.

Keywords: energy, pork quality, residual feed intake