Screening Of SNP And Indel Loci Of Candidate Genes For Milk Fat Traits In Dairy Cows And Their Association Analysis With Milk Production Traits

Milk fat is an important economic trait for dairy cows,and it is also the main target trait for genetic breeding.SNP and Indel sites are the main DNA molecular genetic markers for molecular marker-assisted selection.Combining them with modern breeding techniques is the main method of molecular breeding at present.Based on the collection of complete DHI data from large-scale cattle farms for three consecutive years,this study first carried out the correlation analysis between milk composition of DHI data and somatic cell scores,parity and season;and then respectively used PCR-RFLP and TD-PCR method was used to screen and genotype the SNP and Indel locus of candidate genes for milk fat traits in Chinese Holstein dairy cows;finally,the candidate gene SNPs and Indels locus were associated with the milk production traits of Chinese Holstein dairy cows to clarify the relationship with milk production traits.Relevant molecular marker sites lay the foundation for molecular marker-assisted selection of candidate genes related to milk fat traits.The results of the study are as follows:1.After collecting DHI data from 2017 to 2019,after statistical analysis,it is found that the prevalence of mastitis cows in this farm was low;SCS,milk production,and milk composition are all related,and parity was related to SCS and milk production;At the same time,it is found that when the SCC was between 100 000 and 200 000 units/m L,it will cause milk loss and economic loss.2.35 SNP loci were found in 5 candidate genes;2 SNP loci were identified.The analysis results of genetic parameters of G⁴⁹⁰⁰²⁵A population showed that the loci are evenly distributed in the population and the polymorphic information content was rich.The daily milk production of dairy cows was significantly correlated;the analysis of genetic parameters of G^64695500A population shows that this locus was evenly distributed in the population and the polymorphic information content was rich,and this locus has a very significant correlation with the milk protein rate,which is related to SCS and daily milk production.Significant correlation.3.In the selected 13 candidate genes,2 Indel loci were found and identified;the genetic parameters of rs381960368 loci showed that the loci were evenly distributed in the population and the polymorphic information content was abundant;this loci was related to daily milk production,Milk protein rate and SCS had a significant correlation.The results of population genetic parameters of rs801171594 locus showed that the locus was evenly distributed in the population and the polymorphic information content was rich;the locus showed a significant correlation with the rate of milk protein.4.The identified SNP locus and Indel locus have different degrees of linkage disequilibrium.rs801171594 located in BDNF and G^64695500A located in CYHR1 gene have the highest linkage disequilibrium,and the two SNP loci have higher linkage disequilibrium.In summary,the ^G64695500A and G⁴⁹⁰⁰²⁵A SNPs,rs381960368 and rs801171594 Indels loci identified in this study can be used as molecular markers related to milk production traits in dairy cows,which can be used in molecular marker-assisted selection of dairy cows to promote the genetic breeding process of dairy cows.my country's animal husbandry development contributes to laying the foundation for follow-up experiments.