نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه علوم دامی، دانشکده کشاورزی، دانشگاه زابل، زابل، ایران
2 گروه علوم دامی، دانشکده کشاورزی، دانشگاه زابل، زابل، ایران.
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
The CXCR1 gene is associated with milk production and mastitis resistance/sensitivity in dairy cows. This study aimed to identify polymorphisms in the CXCR1 gene and their association with milk quality traits in Holstein, Sistani, and Sistani×Simmental crossbred cows. Over three months, blood and milk samples were collected from 27 cows (10 Sistani, 10 Holstein, and 7 Sistani×Simmental). Milk components, including fat, protein, lactose, and solids-not-fat percentages, were measured. DNA was extracted using an optimized salting-out method, and a 594 bp fragment of the CXCR1 gene was amplified and sequenced via the Sanger method. Polymorphic regions were identified, and genetic structures were analyzed using MEGA11 and Dnasp5 software. Multiple linear regression and GLM procedures in SAS 9.4 were used to assess associations with milk quality traits. Results indicated limited genetic diversity in the CXCR1 gene among breeds, with Holsteins showing the highest divergence. Ten polymorphic sites and five amino acid changes were identified, with a dN/dS ratio of 1.63, suggesting natural selection's role in gene evolution. Notably, variants in the SNP230 region significantly correlated with fat, lactose, and solids-not-fat percentages in milk. These findings underscore the CXCR1 gene's potential in enhancing dairy cattle breeding programs.
کلیدواژهها [English]
Extended Abstract
Introduction
The CXCR1 gene is one of the candidate genes affecting milk quality and resistance to mastitis in dairy cows. This gene has been mapped on chromosome 2 of cows (BTA2), and studies in different breeds have shown that some specific variants of this gene lead to increased resistance to mastitis. Therefore, the present study aims to identify different variants at the CXCR1 locus and their association with milk quality traits.
Materials and methods: In the present study, 27 purebred Sistani and Holstein cows (10 heads each breed) and Sistani×Simmental crossbred (7 heads) were randomly selected and blood was collected from the jugular vein. In addition, milk quality traits including fat, protein, lactose and solids non-fat percent were analyzed for three months. DNA extraction was performed using the optimized salting-out method. A pair of specific primers was used to amplify a 594 bp fragment of the CXCR1 gene. The amplification products were sequenced using the Sanger method. Genome editing was performed using the Chromas program and low-quality regions were removed, and a 518 bp fragment was used to examine polymorphism among different sequences. Identification of genetic variants, including deletions and additions (Indel) and single-nucleotide polymorphisms as well as genetic structures of populations such as the distance and divergence between and within populations and phylogenetic analysis were performed using MEGA11 and Dnasp5 software. Finally, the association between the variants and milk quality traits was examined using a multiple regression model using the GLM procedure of SAS 9.4 software.Results: In 10 regions of 518 base pairs in length, polymorphism was revealed in 25 different sequences belonging to Sistani, Holstein and Sistani×Simmental crossbred cows after editing the sequences. The 10 regions included 7 single-nucleotide polymorphic sites and three deletions and additions (Indel). The percentage of polymorphism among the total samples was 1.93%. Among the 172 amino acids resulting from the translation of the nucleotide sequence of the CXCR1 locus, five polymorphic regions were revealed, which were located at positions 3, 5, 77, 91 and 102 of the protein chains. Changes in the protein chain included the conversion of glycine to glutamate, threonine to glutamine, serine to leucine, alanine to valine, and serine to proline. In all populations, the percentage of transition substitution was higher than transversional substitution, which is probably due to the greater stability of transition substitutions. Kimura's neutral limit is equal to 0.5, and values higher than 0.5 indicate the role of selection in evolution, and less than 0.5 indicate the absence of selection and the influence of other evolutionary factors such as migration and mutation. The Kimura index coefficient in all breeds was more than 0.5, indicating the role of selection in the evolution of breeds and genetic changes in the mentioned area. The highest divergence rate was in the Holstein population (0.01 bp). Among the divergence rates of different breeds, the highest divergence rate was observed between crosses and Holsteins (0.00354 bp), and the lowest between Sistani and crossbred (0.0014 bp). The coefficient of evolutionary differentiation among breeds was 0.099 bp, with a standard error of 0.056 bp, indicating a very low coefficient of differentiation in the studied area. The number of deletions and additions (Indel) was 3 positions with a length of one base pair. The ratio of mutations that led to amino acid changes (dS) to changes that did not cause amino acid changes (dN) is an index that indicates the role of natural selection in the evolution of populations. In the present study, a pairwise comparison of the sequences from different samples of Sistani, Holstein, and crossbred cows was performed, yielding a value of 1.63, which indicates the involvement of natural selection during the evolution of different cattle breeds. The results of the study of the association of genetic variants in the CXCR1 gene region with milk quality traits showed that polymorphism in the 230 gene region (SNP230) had a significant association with the traits of fat, lactose and solids non-fat percentage. At the SNP230 locus, the allele with higher frequency in the population had a higher effect than the allele with lower frequency in all quality traits of milk.
Conclusions: Genetic variation was observed at the CXCR1 gene locus, but it was limited. Most regions of the gene were conserved across breeds. Association analysis between gene variants and milk quality traits showed significant associations, so it could be a useful marker in dairy cattle breeding programs.
Methodology, S. A., G. R. D. and M. R.; software, S. A., G. R. D. and M. R.; formal analysis, S. A., G. R. D. and M. R. writing—original draft preparation, S. A., G. R. D., M. R., M. V., and A. J.; writing—review and editing, S. A., G. R. D., M. R., M. V., and A. J.; supervision, G. R. D., M. R., All authors have read and agreed to the published version of the manuscript.
Data available on request from the authors.
Acknowledgements
The authors would like to thank all participants of the present study.
The study was approved by the Ethics Committee of the University of Zabol (Ethical cod: IR-UOZ-4398). The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The author declares no conflict of interest.
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