Identification of quantitative trait loci affecting carcass composition in swine: I. Fat deposition traits

One of the major determining factors in the price of market hogs today is backfat depth. Therefore, identification of regions of the genome affecting this trait could be very useful to the swine industry. A large resource population (n = 540) was developed by backcrossing F1 Meishan-White composite females to either Meishan or White composite boars. A genomic scan was conducted by genotyping all animals with microsatellite markers spaced at approximately 20-cM intervals across the entire porcine genome. Breed of origin for all chromosomal segments was determined using multipoint linkage procedures, and a least squares regression analysis was conducted. Nominal P-values were converted to a genome-wide level of significance to adjust for the numerous tests conducted. Traits analyzed were backfat depths at the first rib (FRIB); 10th rib (10th); last rib (LRIB); last lumbar (LLUM) vertebra; the average of FRIB, LRIB, and LLUM (AVBF); and weight of leaf fat (LEAF). Significant quantitative trait loci (QTL) were detected on chromosomes 1, 7, and X. Suggestive evidence for QTL was present on chromosomes 5, 8, 9, 10, 13, and 14. Genotypic means for the loci detected indicated a predominantly additive mode of inheritance. Meishan alleles produced fatter pigs for all loci except those on chromosomes 7 and 10. Additional research should be conducted to refine the estimated position of each QTL and its effect and determine epistatic interactions. These loci should be evaluated in other germplasms to determine whether allelic variation at the QTL exists in other breeds.