Polymorphism of exon 2 of BoLA-DRB3 gene and its relationship with somatic cell score in Beijing Holstein cows.

In the present study, the exon 2 and 3' end sequence of intron 1 of BoLA-DRB3 gene of 211 Beijing Holstein cows was amplified and a uniform fragment of 284 bp was obtained. The genetic polymorphism was investigated by PCR-RFLP using two restriction endonucleases HaeIII and BstYI. Seven genotypes were detected by digesting the PCR products with HaeIII. The frequency of AA, AB, AC, AD, BB, BC and BF genotypes was 0.4638, 0.0193, 0.0193, 0.3478, 0.0290, 0.0386 and 0.0822, respectively. Three genotypes were found by digesting the PCR products with BstYI. The frequency of AA, AB and BB genotypes was 0.0569, 0.2844 and 0.6587, respectively. The relationship between the polymorphisms in exon 2 of BoLA-DRB3 gene and somatic cell score (SCS) in Beijing Holstein cows was analyzed by least squares linear model. No significant difference was detected among least squares means of SCS for seven HaeIII-RFLP genotypes (P > 0.05). As for BstYI-RFLP analysis, least squares mean of SCS for AA was significantly lower than that for AB (P < 0.05) or BB (P < 0.05), and no significant difference was detected between AB and BB genotypes (P > 0.05). BstYI AA was the most favorable genotype and BstYI 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.