| Breeding for disease resistance has a lot of difficulty in research, such as lack of knowledge of resistance properties related to gene, selection traits, selection methods, lower repeatability and high costs of measured. This study was designed to supplement the correlated rationale by4experiments, including the response for H/L or SRBC genetic selection, TLR genes expression and the GWAS for16disease-resistant traits.Experiment1:Three generations of selection for lower ratio of heterophils to lymphocytes (H/L) were completed in a Chinese yellow-feathered chicken line (Jingxing100). Genetic gain for H/L ratio, based on the performance of half-sibs, was22%in the NS line) after three generations of selection. The heritability of61d H/L ratio was0.28. Immune traits compared between the S and NS lines in the final generation (G3) showed that IgG was improved significantly (P<0.05) by selection for lower H/L. While there were no significant difference in.SBRC, AI, and ND between S line and NS line (P>0.05)Experiment2:Four generations of selection for Bi-directional of SRBC were completed in white leghorn chickens. In H, L and C lines, the titer of anti-SRBC, immune traits were measured in each generation (G0-G4) on61d. The heritability of SRBC (61d) was0.26. The genetic correlation between anti-SRBC and IgG, AI, ND and H/L were moderate. In the third and fourth generation, the difference in titers between the selected lines were13.8%,17%and increase in the H over the L lines. Immune traits compared among the H, L and C lines in the final generation (G4) showed that SRBC, AI, ND, and IgM were improved significantly (P<0.05) by selection for SRBC.Experiment3:The real-time PCR method was used to test the expression quantity of TLR1-1, TLR1-2, TLR2-1, TLR2-2, TLR4genes which were the important mode receptor response of innate immune between final selection line (H/L and SRBC) and non-selection line in bursa of Fabricius. In S line (H/L), there were higher expression of TLR1-1, TLR1-2, TLR2-1, TLR2-2than NS line, the TLR2-1gene reached the significantly level (P<0.05). There was no different expression of TLR4. In H and L line, five genes were not reached the significantly level (P<0.05).Experiment4:To identify SNPs associated with16disease-resistant traits, the Illumina60K chips were used to detect the Beijing You and Cobb F2resource population by the GLM. A total of378SNPs were found to be associated with disease-resistant traits at a suggestion significance level;73SNPs reached the significance level;3SNPs reached the high significance level. There no SNPs were detected associated with Spleen, anti-AI titier and RBC at suggestion significance level.After filter,17SNPs at suggestion significance level were associated with thymus and also influence bursa of fabricius.1SNP on8chromosome was associated both MCHC and HCT, and one SNP on15chromosome effected RDW and PDW, and another SNP on1chromosome effected the PDW and PLT.After the GWAS, the genes which nearest the high significance level SNPs (the upstream and downstream500Kb) were founded and explained. Most of genes were associated with cell proliferation and signal transduction, the follow-up studies should be more care about the relationship between the disease-resistant and cell proliferation, signal transduction. Based on the higher significance level (P<5×10-8), combined with a candidate gene method and gene reports, the MAGI2and LOC422090genes were the important candidate gene which influence the weight of thymus and bursa of fabricius, respectively. |
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