Submitted to: American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2002
Publication Date: July 21, 2002
Citation: Sonstegard, T.S., Gasbarre, L.C., Van Tassell, C.P., Padilha, T. 2002. Development of a cattle population for mapping economic trait loci (ETL) affecting parasite resistance [abstract]. American Society Of Animal Science.
The natural genetic variability of the bovine immune system provides an alternative means to control gastro-intestinal (GI) parasite infection without anthelmintics. However, the paradigm of traditional selection has not been applied to parasite resistance due to the difficulty and expense of gathering accurate phenotypes. To validate the potential effectiveness of selection and create a population amenable for mapping, divergent selection was initiated using founder animals from the University of Maryland Wye Angus herd previously observed to be segregating for GI nematode resistance and susceptibility to Ostertagia ostertagi. After nine years of selection, five generations of half-sib progeny (N>350) with phenotypic records from controlled infections have been produced. These progeny fall into three distinct phenotypic classes based on response as measured by eggs per gram (EPG) of fecal matter: innately immune, acquired immune, and immunologically non-responsive. The respective ratio of these calves in the first generation was approximately 1:2:1. Selection based on expected progeny difference (EPD) values for EPG has effectively increased the fraction of innately immune and non-responsive calves. In addition, the range of EPD values has been reduced to half the mean EPG value for calves tested to date, further supporting the role of host genetics in parasite transmission. Currently, this phenotypic data and genotypic data generated using microsatellite markers (N=199) is being analyzed using a multiple locus allelic peeling algorithm (GenoProb) designed to identify the genomic locations of ETL segregating in looped, complex pedigrees. Analysis of the individual pedigrees revealed that > 90\% of the test progeny were paternally descended from a single historic sire, and marker genotypes from 68 sires spanning 8 generations in this paternal pedigree have been added to the ETL analysis. Preliminary analysis of marker information (N=103) revealed an expected heterozygosity index of 50% and polymorphic information content of 45 with an average of 4 alleles per marker. Although power of ETL detection in this population is limited by half-sib family size, genetic analysis of the historic pedigree will provide additional statistical power for refining map position of potential ETL.