| Salmonella enteritidis (SE) contamination of poultry products is a major cause of food-borne disease worldwide. The candidate gene approach for identification of quantitative trait loci (QTL) for chicken response to Salmonella enteritidis (SE) was applied in the current study. The Iowa Salmonella Response Resource Population (ISRRP), formed by crossing outbred broiler sires with three diverse, highly inbred dam lines (two major histocompatibility complex-congenic Leghorn lines G-B1 and G-B2 and one Fayoumi line) was studied. The F1 generation was evaluated as young chicks for either bacterial load in spleen and cecum after pathogenic SE inoculation, or antibody level after SE vaccination. The unique cross between genetically distant parental lines generated a high level of genetic variation, which had the advantage of improving the detection of linkage between markers and QTL. The use of multiple dam lines allowed detection of interaction of sire alleles with the genes of different dam lines. Because the founder lines were genetically distinct and the dam lines are highly inbred (with inbreeding coefficient 99%), the F1 generation was informative for all loci that were heterozygous in the sire.; The natural-resistance associated macrophage protein 1 (NRAMP1), the major histocompatibility complex (MHC) class I and class II, caspase-1 , and the inhibitor of apoptosis proteins 1 (IAP-1) were selected as candidate genes based on their biological functions. Prosaposin was selected as a positional candidate gene based on a previous linkage disequilibrium analysis for identification of QTL using the same population. Single nucleotide polymorphisms (SNPs) of these candidate genes were identified by comparing the sequences of all four sires and two dams from each dam-line, polymerase chain reaction-restriction fragment length polymorphism or single-strand conformational polymorphism, and base excision sequence scanning-T Scan analyses were applied to genotype all F1 offspring of heterozygous sires for each candidate gene. All the candidate genes were associated with bacterial load (in spleen and cecum) after challenge with SE or antibody response to SE vaccination in ISRRP or both. These genes are, therefore, strong potential candidates for application in marker-assisted selection to improve genetic resistance to disease or enhance vaccine efficacy in breeding populations. |
