[Genetic polymorphism of Nramp1 gene and correlation with mastitis in Holstein cattle]

In this research, PCR-SSCP technique was used to analyze the polymorphisms of the exon 11 of Nramp1 gene in Chinese Holstein cattle (n=344), and correlation between polymorphisms of Nramp1 with somatic cell score (SCS) and milk production traits was analyzed. The results show that three genotypes namely AA, BB, and AB were detected. Allele A was predominant and the frequencies of alleles A and B were estimated to be 0.767 and 0.233, respectively. Chi-square test indicated that the polymorphic locus in Chinese Holstein fitted Hardy-Weinberg equilibrium (P>0.05). Sequencing analysis showed two polymorphic sites at positions 200 bp (C/G) and 254 bp (T/G), which resulted in amino acid alteration Ala356Pro and Leu374Met. The least squares means of SCS in Holstein cattle was lower for genotype AA than that for genotypes AB and BB (P<0.05). The least squares means of milk yield of genotype AA and AB were higher than that for genotype BB (P<0.05, P<0.01, respectively). Genotype AA was beneficial to mastitis resistance. This suggested that Nramp1 may be a candidate gene responsible for mastitis in Holstein cattle.