The Polymorphism And Expression Of HSP70-A8 Gene And Their Associationships With DHI Measurement Performances And Physiological Traits In Dairy Cattle

As one of the most important molecular chaperone protein involved in animal heat stress reactions, the effects of HSP70-A8 on dairy production performance and heat resistance were investgated.397 Holstein cattles were used to detectthe polymorphism of HSP70-A8 gene and analyzethe correlations betweenthe polymorphism and DHI production performance of the cows. The polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) technology was used to clone and research the polymorphism of coding region (664 to 5089) ofHSP70-A8 genein Holstein cattles; 10 holstein cattles and the cross-breeding of Holstein X Jersey cows were used to test and compare the relative expression levels of HSP70-A8 gene in blood between different varieties and in different seasons bythe real-time quantitative PCR (qRT-PCR) technology;And the relationship between expression levels and physiological traits were analyzed. The results are as follows:1. The detection of genetic polymorphism of HSP70-A8 geneAll of 8 exonsof HSP70-A8 gene were detected by PCR to test the polymorphism of the gene. There was a G?C mutation in exon 1 at 1522bpwas detected by PCR-SSCP and there was no mutation in the rest 7 exons. The mutation caused the amino acids encoded by glutamine to histidine. Three genotypes (AA/AB/BB) basing the HSP70-A8exon 1mutation were found. And genotypic frequency of AA, AB andBB were 38.56%,31.03% and 30.41% respectively, and the polymorphism information content (PIC) was 0.3733 in the population, they are in moderate polymorphism.According to the results of?2test, the locus is not in Hardy-Weinberg equilibrium in the population.2. The correlation between the genetic polymorphism andDHI measurement performancesThe associationsbetween the polymorphism of HSP70-A8 gene with DHI performance were analysed.It was showed that cows with AA and AB genotype was lower than BB genotype in 305 days fat-corrected milk yield, lactation to date economic-corrected milk yield,305 days fat yield,305 days protein yield and lactation to date protein yield(P<0.01); cows with AA genotype was lower than AB genotype in total fat-corrected milk yield, total milk yield,305 days economic-corrected milk yield and lactation to date fat yield(P<0.05),and cows with AB genotype was lower than BB genotype(P<0.01);Cows with AA genotype had lower somatic cell count than AB and BB genotype.3. The comparison of expression levels of HSP70-A8 gene among several genotype cows under different seasonsThe expression patterns of HSP70-A8 in the same season of three breeds are different.The expression level in F2 generation was significantly higher than purebred and F1 generation in summer (P<0.01); there were no significantly diffrerence between three breeds in autumn and winter.The expression level of purebred and F1 generation had no significantly diffrerence during three seasons; The expression level in F2 generation in summer was significantly higher than winter (P<0.01).4. The difference analysis of physiological traits and it's correlation between the expression levels of HSP70-A8 geneBy the comparative analysis there was no significantly correlation between HSP70-A8 gene expression level and physiological traits.The breathing rate in summer was significantly higher than in autumn and winter;The rectal temperature in summer was significantly higher than in winter;The beats per minute has no significantly diffrerence between three seasons. There is a highly significant positive correlation between rectal temperature and breathing rate (P<0.01).The research suggest that HSP70-A8 gene has significant effect on production of cattles and it can be used as the candidate genetic molecular markers.Cows with BB genotype can be choosed toestablish newheat-resistant Holstein cattle breeds.