Genetic Basis And Genomic Selection Of Longevity Traits In Holstein Cattle

Longevity is a functional trait with high economic value.It not only reflects the cows’ ability to successfully cope with environmental and disease stresses during production,but also reflects the profitability of the pastures,which is the key to the sustainable development of the dairy industry.Many developed countries have done a lot of research on the longevity of dairy cows based on the phenotypic data,and put it into the comprehensive performance index,the weight is 5%-20%,but the genetic gain of longevity is slow and the average lactation parity is still below 3.Therefore,it is very important to carry out the breeding work of high-yield,long-lived and high-quality dairy cows.This study conducted a comprehensive statistical genetic study on longevity traits(including herd life,productive life,number of lactations,stayability)of Holstein cattle in Ningxia,including analysis environmental factors,estimation of genetic parameters,indirect traits selection,genome wide association study and genomic selection(including different methods,response variables and marker densities).The main results are as follows:(1)The herd life and productive life of Holstein cattle were 4.5 and 2.4 years,respectively.The main reasons for the culling of Holstein cattle were reproductive disorder,digestive disorder and udder health,accounting for 20%,20%and 11%,respectively.The active culling only accounted for 14%.The various health events that lead to the culling of Holstein cattle were mainly occurred in the first three parities,lactation days less than 40 and more than 360,and the age of first calving and the culling season also affected longevity of dairy cows.The heritability of longevity traits ranged from 0.048 to 0.305.The genetic correlation between herd life and productive life was 0.998,the genetic and phenotypic correlations between herd life,productive life and number of lactations were increased with parities,but showed the opposite results with stayability.For any of the two number of lactations and stayability traits,the traits with the closest lactation number and stayability usually had higher genetic and phenotypic correlations.(2)The weak genetic correlations were appeared between longevity and fertility traits in heifer(0.222-0.257).However,most of the fertility traits of cows showed negative correlations with longevity traits in different parities(3 parities).The genetic correlations of longevity with day open,interval from calving to first insemination,interval from first to last inseminations in cow ranged from-0.862 to 0.742,and the correlation is more and more strong with the increase of parity.In addition,the approximate genetic correlations between longevity and milk production,conformation,health traits ranged from0.866-0.688,-0.914-0.875,-0.524-0.576,respectively.(3)The total 40 unique SNPs were associated with longevity traits by GWAS,and investigated some known and unknown candidate genes,including PPP2R1A,PPCDC,REEP3,GNMT,SUMO2,KLHDC3 and HJV.In addition,some genes associated with fertility,immune health,conformation,and milk production traits were found,and the study of these genes may provide information and reference for mining genetic markers of longevity in dairy cows.(4)The single(multiple)traits GBLUP and ssGBLUP were used to study genome selection for longevity traits based on different response variables and marker densities.In different marker densities,when EBV was used as a response variable,the accuracy and reliability of single-trait GBLUP was 0.297-0.497 and 0.155-0.211,respectively;The accuracy and reliability of single-trait ssGBLUP was 0.769-0.877 and 0.371-0.410,respectively;The accuracy and reliability of MTGBLUP was 0.4380.667 and 0.216-0.370,respectively;The accuracy and reliability of MTssGBLUP was 0.809-0.911 and 0.487-0.659,respectively.When DRP was used as a response variable,the accuracy and reliability of single-trait GBLUP was 0.099-0.260 and 0.158-0.208,respectively;The accuracy and reliability of single-trait ssGBLUP was 0.276-0.494 and 0.275-0.479,respectively;The accuracy and reliability of MTGBLUP was 0.277-0.396 and 0.195-0.305,respectively;The accuracy and reliability of MTssGBLUP was 0.227-0.581 and 0.493-0.639,respectively.The genomic selection was influenced by different methods,response variables and marker density,and DRP more suitable for longevity’s genomic selection.Single(multiple)trait ssGBLUP was better than single(multiple)trait GBLUP,the multiple trait models were better than single-trait models,and high marker density improved genome prediction.(5)The genomic selection for longevity traits based on fertility traits was carried out by MTGBLUP and MTssGBLUP.When EBV was used as a response variable,the accuracy and reliability of MTGBLUP was 0.058-0.701 and 0.134-0.686,respectively;The accuracy and reliability of MTssGBLUP was 0.126-0.885 and 0.178-0.406,respectively.When DRP was used as a response variable,the accuracy and reliability of MTGBLUP was 0.017-0.275 and 0.16-0.412,respectively;The accuracy and reliability of MTssGBLUP was 0.111-0.527 and 0.202-0.492,respectively.In summary,this study analyzed the genetic basis and investigated some candidate genes closely related to longevity traits of Holstein cattle,and explored the application of genomic selection in longevity traits of Holstein cattle.The results are helpful to evaluate longevity traits of Holstein cattle more accurately and comprehensively,and provide important research basis and reference for making more scientific and comprehensive breeding programs.