Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract only
Publication Acceptance Date: 2/1/2004
Publication Date: 3/15/2004
Citation: Rohrer, G.A., Nonneman, D.J., Ford, J.J., Wise, T.H. 2004. Association of a polymorphism in thyroxine binding globulin with backfat depth in a composite population containing 25% meishan germplasm. Journal of Animal Science 82(Suppl. 2):42-43. Interpretive Summary:
Technical Abstract: A QTL located on the X chromosome for backfat was discovered in a Meishan (ME) x White Composite (WC) population. Recently, we discovered a single nucleotide polymorphism (SNP) in the thyroxine binding globulin gene (TBG) that affects binding affinity of the protein to thyroxine, and is strongly associated with testes size in mature boars. The objective of this study was to determine if the SNP in TBG was associated with backfat. The original study evaluated backcross gilts and barrows weighing about 100 kg. A composite ½ ME ½ WC population was developed and inter se mated for 2 generations. This population was crossed to ½ Landrace ½ Yorkshire pigs and inter se mated for 5 more generations. Backfat of boars (n=60) and gilts (n=136) was determined using ultrasound at about 6 and 7 mo of age, respectively, at the first rib (FRB), last rib (LRB) and last lumbar vertebra (LLM) and each pig genotyped for the TBG SNP. Average backfat (AFT) was also studied. Data were analyzed using SAS GLM with a model that included TBG genotype and age. Gilts and boars were analyzed separately as boars are hemizygous for TBG. TBG genotype was not a significant source of variation for backfat in boars. In gilts the WC TBG allele was dominant to the ME TBG allele. Therefore, the final analysis coded TBG genotypes as homozygous ME or at least one WC allele. TBG genotype was significant for AFT and FRB; LRB approached significance. Homozygotes for the ME allele had 3.9 mm more AFT, 6.0 mm more FRB, 3.2 mm more LRB and 2.5 mm more LLM. These results are similar to the original study where the estimated difference was about 3 mm at each location. While this study does not prove that the TBG SNP discovered causes differences in fat deposition, it does indicate that either TBG or a closely linked gene does affect body composition. Additional studies on this SNP's effect on thyroid function along with intramuscular and subcutaneous fat deposition are underway.