Association Of Single Nucleotide Polymorphisms Of CXCR1 Gene With Susceptibility To Bovine Leukemia

Bovine leukemia is caused by bovine leukemia virus(BLV)which can infect cattle,sheep and other animals.It is a chronic tumor disease and characterized by lymphoid cell hyperplasia,progressive cachexia and high mortality.As one of the important infectious diseases that affects the development of cattle industry,bovine leukemia is widely distributed and exists in almost each cattle country of the world.The seropositivity rate of this disease can even reach to 60%in some cattle population.Many studies from abroad have demonstrated that the immune system plays an important role in the development and progression of bovine leukemia.CXCR1 gene is a key regulator of inflammation,tumorigenesis,proliferation and growth of dairy cattle.Therefore,in the present study 886 Chinese Holstein blood samples were collected to detect bovine leukemia infection by BLV FRET-qPCR.Furthermore,the performance records of cattle production were used to evaluate the effects of bovine leukemia on the lactation performances of different calving season,tested season and lactation stages using multivariate analysis of variance.By direct DNA sequencing,4 SNPs,642 G>A,816 C>A,980 G>A and 1068 G>A,were identified in CXCR1 gene coding region(CDS),which were then genotyped by MALDI-TOF-MS.The relationship between genotype and haplotype of CXCR1 SNPs and bovine leukemia infection was finally analyzed by Logistic regression.Our results provide a reference for molecular marker-assisted breeding of bovine leukemia resistance.The main results are as follows:1.Of the 886 cows,48 were suffered with bovine leukemia,with a positive rate of 5.4%.2.The effects of leukemia on the lactation performances of dairy cow for different calving season,lactation stage,parity and tested seasonwere significant(P<0.01).The milk fat percentage and SCS for positive cattle in spring were significantly lower than that in negative cattle.SCS was significantly lower in the mid lactation for positive cattle than in the negative cattle.The milk fat percentage of late lactation for BLV negative cattle was significantly higher than that of positive cattle.The content of milk urea nitrogen in the third lactation for BLV negative cattle was significantly higher than that in the positive cattle.The SCS for BLV negative cattle which calving in summer and winter was significantly higher than that for BLV positive cattle.3.13 SNPs were found in the CDS region of CXCR gene.The linkage analysis showed that theywere divided into four linkage groups.4 SNPs,including SNPs 642G>A,816C>A,980G>A and 1068G>A,were selected for further analysis.These SNPs were further genotyped by flight mass spectrometry in a large population of Chinese Holstein cow.The predominant genotypes of CXCR1-642,CXCR1-816,CXCR1-980 and CXCR1-1068 were GG,CC,GG and GG,with frequencies of 0.58,0.466,0.60 and 0.658,respectively.The dominant allelic genes were G,C,G and G,and the frequencies were 0.76,0.69,0.78 and 0.81,respectively.8 haplotypes were detected in the 4 SNP loci,of which,the frequency of haplotype GAAG was the highest(0.819),and the frequency of haplotype GCAG was the lowest(0.033).SNP 980 G>A and haplotype GCAG(P = 0.016)were significantly associated with the relative risk of leukemia.The risk of cows which is susceptible to BLV with AA genotype at 980 G>A locus was 5.04 times of that of GG gene,and the risk of cows which is susceptible to BLV with CXCR1 haplotype GCAG was 1.97 times of that of GAGG.