Polymorphism of genes encoding cytokines IL6 and TNF is associated with pig fatness

Porcine fatness is a polygenic trait, but there has been limited success in identifying genes underlying its variation. Three candidate genes for fatness were evaluated: two encoding cytokines, i.e. interleukin-6 (IL6) and tumor necrosis factor-α (TNF), and the gene encoding the heart fatty acid-binding protein (FABP3). The animals were gilts of Polish Large White (n = 191), Polish Landrace (n = 239), and synthetic line 990 (n = 242). Four novel single-nucleotide polymorphisms (SNPs) were detected: g.61T > C (GenBank acc. no. EF450127), g.6464C > T (X54859), and g.701T > C (X98558) in the promoter regions of the IL6, TNF and FABP3 genes, respectively, and g.8653A > G (X54859) in exon 4 of TNF. The gilts were dissected when they reached the weight of 100 kg, and 12 traits were analyzed: abdominal fat weight, backfat thickness (BFT) measured at 7 points, lean meat yield, intramuscular fat percentage (IMF), average daily gain, and feed conversion ratio. Multiple breed-specific associations were calculated between fatness traits and SNPs in the promoter regions of IL6 (g.61T > C, 0.006 ≤ P ≤ 0.009) and TNF (g.6464C > T, 0.002 ≤ P ≤ 0.005). Our results support the hypothesis that the polymorphisms of IL6 and TNF are associated with fatness variation within pig breeds.