Single nucleotide polymorphisms in the imprinted bovine insulin-like growth factor 2 receptor gene (IGF2R) are associated with body size traits in Irish Holstein-Friesian cattle

The regulation of the bioavailability of insulin-like growth factors (IGFs) is critical for normal mammalian growth and development. The imprinted insulin-like growth factor 2 receptor gene (IGF2R) encodes a transmembrane protein receptor that acts to sequester and degrade excess circulating insulin-like growth factor 2 (IGF-II) - a potent foetal mitogen - and is considered an important inhibitor of growth. Consequently, IGF2R may serve as a candidate gene underlying important growth- and body-related quantitative traits in domestic mammalian livestock. In this study, we have quantified genotype-phenotype associations between three previously validated intronic bovine IGF2R single nucleotide polymorphisms (SNPs) (IGF2R:g.64614T>C, IGF2R:g.65037T>C and IGF2R:g.86262C>T) and a range of performance traits in 848 progeny-tested Irish Holstein-Friesian artificial insemination sires. Notably, all three polymorphisms analysed were associated (P ≥ 0.05) with at least one of a number of performance traits related to animal body size: angularity, body depth, chest width, rump width, and animal stature. In addition, the C-to-T transition at the IGF2R:g.65037T>C polymorphism was positively associated with cow carcass weight and angularity. Correction for multiple testing resulted in the retention of two genotype-phenotype associations (animal stature and rump width). None of the SNPs analysed were associated with any of the milk traits examined. Analysis of pairwise r ² measures of linkage disequilibrium between all three assayed SNPs ranged between 0.41 and 0.79, suggesting that some of the observed SNP associations with performance may be independent. To our knowledge, this is one of the first studies demonstrating associations between IGF2R polymorphisms and growth- and body-related traits in cattle. These results also support the increasing body of evidence that imprinted genes harbour polymorphisms that contribute to heritable variation in phenotypic traits in domestic livestock species.