Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2003
Publication Date: N/A
Interpretive Summary: Due to increasing concerns over the extensive drug use in US poultry production and higher rate of condemnation and mortality due to diseases in commercial broiler populations, there is an increasing interest to develop drug-free control strategies for many poultry diseases. One of these new control methods involves the development of DNA marker-dependent selection strategy. However, lack of information on the nature of DNA markers which are associated with diseases and production parameters hinders the progress in this effort. In this study, scientists at ARS and University of Delaware collaborated to evaluate the performance of three commercial broiler lines in response to two major poultry pathogens, coccidian and Marek¿s virus. This study demonstrated that the three lines differ for immune response and disease resistance to coccidiosis and Marek¿s disease although those broiler lines have been intensively selected for productivity and general livability. The results indicate a need for more studies emphasizing the genetics of host immune response and disease resistance in order to develop a logical marker-assisted control strategies for coccidiosis and other poultry diseases.
Identification of genetic markers for immune response and disease resistance in commercial chicken populations will facilitate breeding programs that use marker-assisted selection. In order to identify candidate markers, lines with the most divergent phenotypes are usually crossed to generate resource mapping populations; for example, either backcross or F2 populations. Linkage between the genetic marker and the phenotypic trait locus is then tested in the mapping population. Few commercial outbred chicken lines have been characterized for immune response and disease resistance. Therefore, the goal of the current research was to evaluate the phenotypic variation among three commercial broiler pure lines for antibody response to SRBC, and in resistance to two economically-important poultry diseases, Marek's disease (MD) and coccidiosis (Eimeria acervulian). Chicks from each line were received and separated into three experimental studies to evaluate each of their responses. In summary, broiler line 3 had significantly lower primary and secondary antibody responses to SRBC compared to the other two lines, and non-vaccinated birds from line 3 were also more susceptible to MD. With coccidiosis, the response was complex, and ranking of the lines was dependent on the age of infection, and whether it was a primary or secondary challenge. With primary challenge, line 1 was most susceptible at an early age (d30), whereas line 3 was susceptible at an older age (d58). Upon secondary challenge, broiler line 1 remained susceptible at d30, but line 2 was more susceptible at d58. Thus, although the broiler lines have been intensively selected for productivity and general livability, this study also demonstrates that the lines differ for immune response and disease resistance. Based on this phenotypic variation, lines 1 and 3 were chosen to establish a mapping population for studying genetic markers associated with MD and coccidiosis in commercial broilers.