Submitted to: Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/11/2005
Publication Date: 11/1/2005
Citation: McElroy, J.P., Dekkers, J.C., Fulton, J.E., O'Sullivan, N.P., Soller, M., Lipkin, E., Zhang, W., Koehler, K.J., Lamont, S.J., Cheng, H.H. 2005. Microsatellite markers associated with resistance to Marek's disease in commercial layer chickens. Poultry Science. 84:1678-1688. Interpretive Summary: Marek's disease (MD) is an economically-important disease of chickens caused by a pathogenic virus. Currently, vaccines have controlled the problem but new emerging viral strains that vaccines cannot control are being encountered more frequently. To help combat MD, chickens are being selected for genetic resistance, which augments vaccinal control measures. Biotechnology may greatly enhance the rate of poultry breeding improvement by identifying the genes responsible for conferring resistance. Previous studies in experimental chicken lines indicate that it is possible to identify the chromosomal regions containing genes conferring resistance to MD. In the current study, we asked the question of whether we could perform the same type of analyses using elite commercial chicken lines and if the results from the experimental and commercial lines were comparable. In fact, a number of regions were identified, many of which were identical to the earlier results. This indicates that it is possible to identify MD resistance genes in commercial chicken lines, which could be select and generate more disease-resistant chickens. Furthermore, our results indicate that experimental lines are good models for understanding genetic resistance to disease. Ultimately, consumers will benefit as losses due to disease are reduced.
Technical Abstract: The objective of this study was to identify quantitative trait loci (QTL) conferring resistance to Marek's disease (MD) in commercial layer chickens. To generate the resource population, two partially inbred lines that differed in MD-caused mortality were intermated to produce five backcross (BC) families. Vaccinated chicks were challenged with very virulent plus MD virus strain 648A at 6 d and monitored for MD symptoms. A recent field isolate of the MD virus was used because the lines were resistant to commonly used, older laboratory strains. Selective genotyping was employed using 81 microsatellites selected based on prior results with selective DNA pooling. Linear regression and Cox proportional hazard models were used to detect associations between marker genotypes and survival. Significance thresholds were validated by simulation. Seven and six markers were significant based on proportion of false positive and false discovery rate thresholds less than 0.2. Seventeen markers were associated with MD survival considering a comparison-wise error rate of 0.10, which is about twice the number expected by chance, indicating that at least some of the associations represent true effects. Thus, this study shows that loci affecting MD resistance can be mapped in commercial layer lines. More comprehensive studies are under way to confirm and extend these results.