Submitted to: World Congress of Genetics Applied in Livestock Production
Publication Type: Proceedings
Publication Acceptance Date: May 5, 2002
Publication Date: August 19, 2002
Citation: GASBARRE, L.C., SONSTEGARD, T.S., VAN TASSELL, C.P., PADILHA, T. DETECTION OF QTL AFFECTING PARASITE RESISTANCE IN A SELECTED HERD OF ANGUS CATTLE. WORLD CONGRESS OF GENETICS APPLIED IN LIVESTOCK PRODUCTION. 2002.
Interpretive Summary: Roundworm parasites that live in the gut severely reduce the efficiency of raising cattle on pasture. An alternative for control of parasite transmission in cattle is to use markers that identify differences in cattle DNA in the selection of breeding stock. But first the areas on the DNA that affect resistance to the parasites must be identified. Because different parasites vary in susceptibility to the animal's immune system, identification of these areas of DNA requires 1. extensive characterization of how and why certain animals are resistant or susceptible, 2. extensive families of cattle where their lineage can de traced, and 3. a complex statistical analysis. We made such a cattle family in our laboratory that resulted in each sire producing between 5 and 13 calves that were half-brother or half-sister. In characterizing the animals we were able to identify certain samples taken from the cattle that were able to accurately measure the number of parasites that infected the animals. To characterize the DNA of the 350 animals produced, we used 216 markers to identify areas of DNA that showed variations in the different cattle. This required more than 95,000 different tests of the animal DNA. Of the 216 areas tested, 200 were useful, and these 200 regions cover the entire DNA at regularly spaced intervals. Because the family structure is complicated we had to design a sophisticated statistical analysis, which we are now using to identify the areas of the DNA that affect resistance to the parasites.
Gastrointestinal (GI) nematodes severely reduce the efficiency of raising cattle on pasture. An alternative for control of parasite transmission in cattle is a DNA marker-based selection developed after identification of ETL influencing acquired or innate parasite resistance. Because different parasite species vary in susceptibility to the same types of immune responses, identification of ETL affecting parasite resistance requires extensive phenotypic analysis embedded in a population structure amenable to statistical analysis. To identify these ETL, a divergent selection program was initiated in our laboratory that has resulted in paternal half-sib families ranging from 5-13 progeny/sire. This program has identified accurate indicator variables based on correlations between phenotypic measurements, parasite load, and immune response. A total of 216 microsatellite markers have been tested, and a complete sets of marker genotypes (n > 95,000)were generated for 200 markers spaced at regular intervals (~20 cM ) in approximately 350 phenotyped animals . A multiple locus allelic peeling algorithm (Thallman et al. 1999a; Thallman et al. 1999b)is being used to identify parasite resistance ETL. We are currently completing this analysis.