Turkish Journal of Veterinary & Animal Sciences




The aim of this study was to investigate the promoter polymorphisms of the growth hormone (GH1), growth hormone receptor (GHR), insulin-like growth factor (IGF-I), and prolactin (PRL) genes, and the correlation of the expression levels of these genes with lactation and daily milk yields in Holstein cattle. A total of 154 lactating Holstein cows raised in the Central Anatolia Region of Turkey, with a mean age of 5.4 years and a mean body weight of 571.7 kg, constituted the study material. Each blood sample was examined by real-time PCR for mRNA expression levels and the promoter polymorphisms of the GH1, GHR, IGF-I, and PRL genes. The only statistically significant difference (P = 0.029) was observed in the daily milk yield between the GH1 genotypes, where the TT genotype cows had higher daily milk yields than cows of the CC and CT genotypes. Moderate negative correlations were found between the expression levels of GHR (r = -0.490, P %lt; 0.001), IGF-1 (r = -0.481, P < 0.001), PRL (r = -0.383, P < 0.029), and the lactation milk yield. There were also low negative correlations between the expression levels of the GHR (r = ?0.262, P = 0.007), IGF-1 (r = -0.264, P = 0.006), PRL (r = -0.215, P = 0.029), and the daily milk yield. However, these relationships did not exist between the expression levels of GH1 and lactation (r = -0.084, P = 0.386) and the daily milk yields (r = -0.043, P = 0.656). Based on the results, it is suggested that GH1 could be used as a genetic marker in the selection of breeder animals for daily milk yield.


Dairy cattle, marker genes, milk yield, single nucleotide polymorphism, gene expression

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