The aim of the present study was to determine the frequency of the two polymorphic variants located in intron 4 of the gene coding for insulin-like growth factor 1 receptor (IGF1R) in the examined herd of 184 Holstein-Friesian cows and to search for the association between these polymorphisms and the selected milk performance traits. The IGF1R gene polymorphism was identified with PCR-RFLP using the HinfI and Mph1103I restriction enzymes. For the IGF1R/HinfI polymorphism, the highest frequency was found for the BB genotype (0.49), a similar one was in the case of the AB genotype (0.45) and the lowest one was for the AA genotype (0.04). The frequency of alleles was as follows: allele A – 0.28 and allele B – 0.72. Statistical analysis showed that the analysed polymorphism significantly affected milk yield, milk protein yield (P≤0.01) and milk fat yield (P≤0.05), favouring the BB genotype. For the IGF1R/Mph1103I polymorphism, no individuals with the AA genotype were recorded. A high frequency of allele B (0.94) was found. No significant effect of the IGF1R/Mph1103I polymorphic site on the yield of milk, fat and protein was shown. Statistically significant differences (P≤0.05) were observed only for the percentage content of milk fat and protein with indication on the positive effect of the BB genotype.

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