Abstract：In the present study, the exon 2 of BoLA-DRB3 gene of 489 Holstein cows and 40 Holstein bulls in Hebei province was amplified and a uniform fragment of 284 bp was obtained. The 284 bp PCR product was digested with restriction endonuclease BstYⅠ, and genetic polymorphism was investigated by PCR-RFLP. Three genotypes (AA, AB and BB) were found in 489 Holstein cows by digesting the PCR product with BstYⅠ, and the frequency of AA, AB and BB genotypes was 0.078, 0.380, 0.542, respectively. Two genotypes (AB and BB) were found in 40 Holstein bulls, and the frequency of AB and BB genotypes was 0.250, 0.750, respectively. The fitnesstest showed that both Holstein cows and bulls were in Hardy-Weinberg equilibrium (cows: χ2 =0.45, P=0.799>0.05; bulls: χ2 =0.82, P=0.665>0.05). The relationship between exon 2 of BoLA-DRB3 gene and somatic cell score (SCS) in Holstein cows was analyzed by least squares linear model. Least squares mean of SCS for AA was significantly lower than that for AB (P=0.0098<0.01) or BB (P=0.00009<0.0001), least squares mean of SCS for AB was significantly lower than that for BB (P=0.0096<0.01). AA was the most favorable genotype, BB was the most unfavorable genotype for mastitis resistance. The information found in the present study is very important for improving mastitis resistance in dairy cattle by marker assisted selection.
