Abstract：The genetic polymorphisms of partial sequence of DNA-dependent protein kinase gene (PRKDC) in 210 Holstein cows were detected by PCR-SSCP with five pairs of primers P1~P5. Five polymorphic sites, i.e. G34126A, C77353T, T77384G, C77406T and indel (C) at site of 77408 bp were found, and G34126A mutation caused an amino acid change of serine to asparagine. For the amplified fragment of P2, three genotypes (AA, AB and BB) were found in 210 Holstein cows, and the genotype frequency of AA, AB and BB was 0.186, 0.433 and 0.381, respectively. For the amplified fragment of P3, five genotypes (CC, CD, DD, CE and DE) were found in 210 Holstein cows, and the genotype frequency of CC, CD, DD, CE and DE was 0.786, 0.129, 0.009, 0.067 and 0.009, respectively. The relationship between polymorphisms of PRKDC gene and somatic cell score (SCS) in Holstein cows was analyzed by least squares linear model. Results showed that least squares mean of SCS for AA was significantly lower than that for AB or BB (both P<0.05), and the difference of the least squares means for SCS between AB and BB was not significant (P>0.05). AA was the most favorable genotype, BB was the most unfavorable genotype for mastitis resistance. The difference of the least squares means for SCS among CC, CD, DD, CE and DE was not significant (P>0.05). The results preliminarily indicated that allele A of G34126A polymorphic site of PRKDC gene is a potential DNA marker for improving mastitis resistance in cows.
