Evaluation of serum insulin-like growth factor binding proteins and the insulin-like growth factor binding protein-2 locus for potential associations with growth, carcass merit and meat quality in beef cattle

The presence of growth-promoting factors in serum and tissues has been recognized since the beginning of the last century. Recent advances in protein chemistry and the development of molecular biology techniques have resulted in the identification, at both the gene and protein level, of several biological activities suspected to belong to the insulin-like growth factor (IGF) family. The IGFs (IGF-I and -II) are unique among peptide growth factors in that they circulate in blood tightly bound to a group of proteins known as the insulin-like growth factor binding proteins (IGFBP), which modulate IGF activity. The objectives of this study were to evaluate relative abundance of serum IGFBP in Angus cattle divergently selected (high vs. low) for serum IGF-I concentration, to identify DNA sequence variation (polymorphisms) at the bovine IGFBP-2 locus, and to investigate potential associations between IGFBP and traits of economic importance. No significant effect of line was observed in the expression of specific IGFBP species in periods before and after the selection lines were divergent for serum IGF-I concentration. However, heifer calves consistently expressed higher levels of the 34kDa IGFBP species than bulls. This protein was determined to be bovine IGFBP-2 by immunoblot analysis. When the lines were divergent for serum IGF-I, IGFBP-2 was negatively correlated with serum IGF-I concentration and body weights measured throughout the postweaning performance test. Also, two restriction fragment length polymorphisms (RFLP) were identified at the IGFBP-2 locus and both were found to be segregating in different breeds of cattle.{09}IGFBP-2 RFLP alleles identified with the restriction endonuclease Hind III were found to be associated with growth and carcass traits. Results of this study support IGFBP-2 as an important regulator of somatic growth in cattle and further investigation of this gene is warranted.