The IGF 1 pathway genes and their association with age of puberty in cattle

Summary Insulin‐like growth factor I ( somatomedin C ) ( IGF 1 ) influences gonadotrophin‐releasing hormone ( G n RH ) neurons during puberty, and G n RH release guides pubertal development. Therefore, genes of the IGF 1 pathway are biological candidates for the identification of single‐nucleotide polymorphisms ( SNP s) affecting age of puberty. In a genome‐wide association study, genotyped heifers were Tropical Composite ( TCOMP , n  = 866) or Brahman ( BRAH , n  = 843), with observation of age at first corpus luteum defining puberty. We examined SNP s in or near genes of the IGF 1 pathway and report seven genes associated with age at puberty in cattle: IGF 1 R , IGFBP 2 , IGFBP 4 , PERK ( HUGO symbol EIF 2 AK 3 ), PIK 3 R 1 , GSK 3 B and IRS 1 . SNP s in the IGF 1 receptor ( IGF 1 R ) showed the most promising associations: two SNP s were associated with puberty in TCOMP ( P  < 0.05) and one in BRAH ( P  = 0.00009). This last SNP explained 2% of the genetic variation ( R 2  = 2.04%) for age of puberty in BRAH . Hence, IGF 1 R was examined further. Additional SNP s were genotyped, and haplotypes were analysed. To test more SNP s in this gene, four new SNP s from db SNP were selected and genotyped. Single SNP and haploytpe analysis revealed associations with age of puberty in both breeds. There were two haplotypes of 12 IGF 1 R SNP s associated with puberty in BRAH ( P  < 0.05) and one in TCOMP ( P  < 0.05). One haplotype of two SNP s was associated ( P  < 0.01) with puberty in BRAH , but not in TCOMP . In conclusion, the IGF 1 pathway appeared more relevant for age of puberty in Brahman cattle, and IGF 1 R showed higher significance when compared with other genes from the pathway.