Genomic tools to improve parasite resistance

The natural genetic variability of the ruminant immune system provides a fe asible means to control gastrointestinal (GI) parasite infection without an thelmintics. However, the paradigm of traditional selection has not been ef fectively applied to the moderately heritable traits of parasite resistance (h approximate to 0.3) due to the difficulty and expense of gathering accu rate phenotypes in a commercial production setting. These characteristics m ake host traits related to GI nematode infection ideal candidates for genom ics-based research. To initiate explanation of important allelic difference s, economic trait loci (ETL) are being identified and mapped using a resour ce population of Angus cattle segregating for GI nematode resistance and su sceptibility to the two most common nematode parasites of US cattle, Ostert agia ostertagi and Cooperia oncophora. The population is composed of five g enerations of half-sib progeny with complete phenotypic records produced fr om controlled infections. To detect the genomic locations of the three dist inct phenotypic traits being expressed (innately immune, acquired immune, a nd immunologically non-responsive), genotypes have been generated for DNA m arkers (N = 199) spaced at regular intervals (similar to 20 cm intervals) t hroughout the entire genome (3000 cm), Although initial ETL detection may b e limited by half-sib family size, the unique structure of this population provides additional statistical power for refining map position of potentia l ETL. After allele frequency and contribution to phenotype are determined in this population, marker tests associated with ETL most beneficial for co ntrolling parasite infection can be accurately used for selection. Comparat ive map and functional genomic information from humans and other species of biomedical importance will be utilized in further investigations to elucid ate the genes underlying ETL. Published by Elsevier Science B.V.