Study On Polymorphism Of MHC And Its Relationship With Somatic Cell Counts In Cow Milk

MHC is a chromosomal region consisting of a group of closely linked loci which are highly polymorphic, and plays a central role in the immune system. The molecular genetic polymorphisms were investigated for MHC-DRB3 locus in Beijing Holstein cow by PCR-RFLP. Furthermore, the second exon of DRB3 was cloned and sequenced after amplication. Homologies of the nucleotide sequence and amonia acid sequence of the fragment were compared among Mongolian cattle, Human Swedish Red and White cattle Mongolian Sheep and Spanish goat.Following were the results.1. By digesting the PCR product with BstY I and Hae III, there were five polymorphic sites at position 150, 154,173, 182, and 202 in the second exon of Beijing Holstein cow DRB3 gene. 2 alleles and 5 alleles were found respectively, gene frequency was 0.20, 0.80; 0.6570, 0.0990, 0.0290, 0.1739, 0.0411. Statistical results showed that polymorphic locus for BstY I of Beijing Holstein cow DRB3 locus fitted with Hardy-Weinberg equilibrium (P>0.05), polymorphic locus for Hae III of Beijing Holstein cow DRB3 locus didn't fit with Hardy-Weinberg equilibrium (P<0.01).2. Least squares mean of Somatic Cell Score for Hae III AC genotype was the highest, and Least squares mean of Somatic Cell Score for Hae III AD genotype was thelowest; Least squares mean of Somatic Cell Score for Hae III AD genotype was significantly lower than those for Hae III AA genotype (P<0.05) in cow populations; There were no significant correlations among other genotypes in cow populations.Least squares mean of Somatic Cell Score(SCS) for BstY I BB genotype is the highest, and Least squares mean of Somatic Cell Score for BstY I AA genotype is the lowest. Least squares mean of Somatic Cell Score for BstY I AA genotype was significantly lower than those for BstY I AB BB genotype (P<0.01) in cow populations. There were no significant correlations among other genotypes in cow populations.3. Comparative analysis showed that the homologies of the nucleotide sequence and amonia acid sequence of DRB3 gene between Beijing Holstein cow and Mongolian, Human, Swedish Red and White breed, Mongolian Sheep and Spanish goat are high.