A QTL on pig chromosome 4 affects fatty acid metabolism: Evidence from an Iberian by Landrace intercross

Three Iberian boars were bred to 31 Landrace sows to produce 79 F-1 pigs. S ix F-1 boars were mated to 73 F-1 sows. The F-2 progeny from 33 full-sib fa milies (250 individuals) were genotyped for seven microsatellites spanning the length of chromosome 4. Least squares procedures for interval mapping w ere used to detect quantitative trait loci (QTL). A permutation test was us ed to establish nominal significance levels associated with QTL effects, an d resulting probability levels were corrected to a genomewide basis. Observ ed QTL effects were (genomewide significance, position of maximum significa nce in centimorgans): percentage of linoleic acid in subcutaneous adipose t issue (<0.01, 81); backfat thickness (<0.01, 83); backfat weight (<0.01, 80 ); longissimus muscle area (0.02, 83); live weight (0.19, 88); and percenta ge of oleic acid in subcutaneous adipose tissue (0.25, 81). Gene action was primarily additive. The Iberian genotypes were fatter, slower growing, and had lower linoleic and higher oleic acid contents than Landrace genotypes. The interval from 80 to 83 cM contains the FAT1 and A-FABP loci that have been shown previously to affect fat deposition in pigs. This is the first r eport of a QTL affecting fatty acid composition of subcutaneous adipose tis sue in pigs and provides a guide for the metabolic pathways affected by can didate genes described in this region of chromosome 4.