A paternally imprinted QTL for backfat and lean meat percentage is located at the IGF-II locus of porcine chromosome (SSC) 2 (Nezer et al., 1999, Nature Genetics 21, 155-156: Jeon et al., 1999, Nature Genetics 21, 157-158). It explains 25 % of the variation in leanness in experimental crosses while it does not influence daily gain or pH of meat.

The purpose of this study was to investigate if this QTL can be used in commercial selection programs in order to increase uniformity of slaughter pigs without influencing the meat quality. Since the QTL is characterized by paternal imprinting, the boar should pass the full effect of the QTL, regardless of the genotype of the sows. This way the use of homozygous terminal sires should increase the uniformity of hogs.

Terminal sires (SEGHERSmaxiMus) that are homozygous for the favorable allele of the IGF-II QTL were produced. A field trial was performed with these sires and carcass and meat quality characteristics were compared with hogs from non-selected terminal boars and with the average of the plant top 25 %.

Carcass and meat quality data were compared between 211 hogs from homozygous boars and 1,467 hogs from unselected boars. All data confirmed that hogs from homozygous boars were leaner and more uniform. Backfat thickness was reduced with 0.09 inches. Average lean meat %, ham %, loin % and belly % were increased by 1.98%, 0.31%, 0.43% and 0.92 % respectively. This increase was due to elimination of the animals with a higher backfat thickness rather than to a general enhancement of the lean meat % of all animals involved. Hence, the variation, as calculated through the coefficients of variation on each of these parameters, was reduced 25 % on average.

To measure meat quality, pH and color were recorded. Hogs from homozygous boars and those from unselected boars both had pH values (pH after 24 h of 5.77 as to 5.78) and color values (Minolta L* of 44.57 as to 43.08) within the optimal range.

As compared to the average of plant top 25 %, hogs from homozygous boars were leaner (+0.64 % for lean meat, +0.39 % for ham, +0.43 % for loin, +0.16 % for belly).

It is concluded that marker assisted selection for terminal sires that are homozygous for the favorable allele of the IGF-II polymorphism increase uniformity and leanness in market hogs without influencing meat quality.