It is widely accepted that hormones, growth factors and other agents exert their biological effects on target tissues by binding to specific receptors on the plasma membrane. The variability in constituent sequences of growth hormone receptor (GHR) gene is very important because of its major role in mammary gland development. The aim of the present study is to detect polymorphism in promoter region of GHR gene and its association with milk related traits in Holstein cows. Blood samples were randomly collected from 93 Holstein cows, transported to the laboratory and stored at -20°C for further analysis. DNA was extracted using modified salting-out method and a fragment of 836 base pair from promoter region of GHR gene was amplified by a specific primer pairs using polymerase chain reaction (PCR). The PCR products were digested by AluI restriction enzyme and electrophoresed on 2% agarose gel. Result of enzyme digestion for GHR gene, showed allele AluI(-) with the fragment sizes of 14, 75 and 747, and allele AluI(+) with the fragment sizes of 14, 75, 145 and 602 base pairs. Frequency estimation ofAluI(-) and AluI(+) alleles were 56 and 44%, respectively, and mean of heterozygosity was 0.49. Statistical analysis showed that cows with AluI(+) allele had significantly higher milk protein and fat percentage at first lactation compared with cows with AluI(-/-), while there was no significant relation between different genotypes and other traits.
Key words: Growth hormone receptor, polymorphism, milk, Holstein.
GHR, Growth hormone receptor; PCR-RFLP, polymerase chain reaction-restriction fragment length polymorphism; Jak2, janus kinase2; STAT5,signal transducer and activator of transcription 5; T, thymine; A, adenine; G,guanine; SNP, single nucleotide polymorphism; EDTA, ethylenediaminetetraacetic acid; IGF-I, insulin-like growth factor I; SCC, somatic cell count; BW, body weight;DW, dressed weight; SFT, subcutaneous fat thickness; HW, hatch weight.
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