Analysis On Genetic Structure Of Dapulian And Wenxin Black Pigs And Polymorphism Of Disease-resistance Genes

China is rich in livestock and poultry germplasm resources,but due to the lack of corresponding protection,some local varieties are in crisis of extinction.Dapulian Pig,as one of the local breeds listed in the List of National Animal Genetic Resources Protection in China,has excellent characteristics.However,with the introduction and popularization of foreign improved lean-type pigs,Dapulian pig has been greatly impacted and even endangered.Therefore,it is necessary to carry out in-depth research on and protect the genetic diversity of Dapulian pig germplasm resources.Wenxin Black Pig was obtained by crossbreeding Dapulian pig as the female parent with Berkshire as the male parent,which inherited the good characteristics of both breeds.Previous laboratory studies have shown that genetic differences in hosts result in differences in susceptibility to PRRSV and PCV2-related diseases among different pig breeds,and four molecular markers against PRRSV and PCV2 have been identified.In this study,the genetic structure of Dapulian pig and Wenxin Black pig germplasm resources was analyzed to provide molecular basis for their protection and utilization,and then Wenxin black pig disease resistance breeding was conducted using genetic marker assisted breeding method.On the basis of actual production,excellent individuals with disease resistance and high yield were screened out to improve their economic benefits.The specific research content and results are as follows:（1）The population genetic structure of 49 Dapulian pigs and Wenxin black pigs was analyzed with Zhongxin no 1 DNA chip.The results showed that the 49 Dapulian pigs and Wenxin Black pigs could be divided into five families,which were Family A,Family B,Family C,Family D and "Others",where Families A,B,C and D all had male pigs,but the number of male and female pigs and their genetic relationship were not balanced among different families.A total of 1521 ROH fragments were detected in 49 samples,of which1,198 ROH fragments were detected in the Dapulian pig sample and 323 ROH fragments were detected in the Wenxin Black pig sample.The average ROH length of the Dapulian pig was 342.29（215.51）MB,and the largest number of individuals with the total ROH length of0–100 MB was about 20%,with the numbers of 15–20 and 46–50 samples accounting for20%.The average total ROH length of Wenxin Black pig was 139.44（88.75）MB,among which,the individuals with the total ROH length of 51–100 MB accounted for 42.86% and the ones with 16–20 samples accounted for the most.The average inbreeding coefficient of this population calculated based on ROH value was 0.12,indicating that the inbreeding degree of this population was high.The average inbreeding coefficient of Dapulian pig population was 0.14 0.09,while that of Wenxin Black pig population was 0.06 0.04.Through the comparison of ROH and inbreeding coefficient between Dapulian and Wenxin Black pigs,it was indicated that the inbreeding degree of Dapulian Pig population was significantly higher than that of Wenxin Black Pig.（2）Based on the four DNA molecular markers of disease-resistance to PRRSV and PCV2 found in the early stage of our laboratory,the SNP chip typing technology and the generation sequencing technology were used to conduct disease resistance breeding for the populations of Dapulian and Wenxin Black pigs.On the premise of ensuring its production performance,individuals with genotypes resisting PRRSV and PCV2 were screened out,for example,the mi R-122 gene only reserved genotype TT individuals,the SERPINA1 gene only reserved genotype GG individuals,the CYP3A88 gene only reserved genotype TT individuals,the USP18 gene only reserved genotype GG individuals,and the other individuals were phased out,so as to achieve disease resistance breeding.（3）Through the method of genetic marker assisted breeding,the Mx1 gene polymorphism in the DNA samples of 108 Wenxin Black pigs is detected,disease resistance breeding is carried out on the Wenxin Black pig population,individuals with genotype BB and excellent production performance and strong disease resistance are retained,and those of AA and AB are gradually eliminated,so that early selection is realized,and the disease resistance breeding of pigs becomes simple,efficient,rapid and accurate.