Polymorphism in promoter region of growth hormone receptor is associated with potential production capacity of insulin‐like growth factor‐1 in pre‐pubertal Holstein heifers

Summary Insulin‐like growth factor‐1 ( IGF ‐1) is one of the important factors for growth, milk production and reproductive functions and mainly released from the liver in response to growth hormone ( GH ) via GH receptor ( GHR ) in cattle. Recently, some single nucleotide polymorphisms ( SNP s) were identified in the bovine GHR gene. Some GHR ‐ SNP s were shown to be related to plasma IGF ‐1 concentration in cattle. Hence, the capacity to IGF ‐1 production in the liver might be affected by GHR ‐ SNP and associated with performance in the future. This study examined whether GHR ‐ SNP is associated with IGF ‐1 production in the liver of pre‐pubertal heifers. In 71 H olstein calves, blood samples for genomic DNA extraction were obtained immediately after birth. To genotype the GHR ‐ SNP s in the promoter region, polymerase chain reaction ( PCR ) products were digested with restriction enzyme Nsi I (cutting sites: AA , AG and GG ). All heifers at 4 months of age were intramuscularly injected with 0.4 mg oestradiol benzoate. Blood samples were obtained from the jugular vein just before (0 h) and 24 h after injection. The number of AA , AG and GG at the Nsi I site was 0, 17 and 54 respectively. In AG and GG , plasma GH concentrations were higher pre‐injection than 24 h post‐injection (p < 0.01). Moreover, plasma GH concentrations in AG post‐injection were higher than in GG (p < 0.05). In contrast, the GG genotype exhibited higher plasma IGF ‐1 concentrations in pre‐injection than post‐injection (p < 0.01), although oestradiol did not change IGF ‐1 concentration in the AG genotype. We conclude that the GG polymorphism in the promoter region of GHR is associated with a higher potential capacity of IGF ‐1 production in the liver of cattle.