Identification of quantitative trait loci affecting gastrointestinal parasite resistance in an experimental Angus population.

DNA markers associated with quantitative trait loci (QTL) affecting host tolerance to gastrointestinal (GI) parasite infection are ideal targets for marker-assisted selection. However, few studies in cattle have attempted to identify this type of QTL due to the difficulty of generating accurate phenotypic data from a resource population with adequate statistical power for detection. For this effort, we amassed fecal egg count (FEC) measures from annual natural field challenges with GI nematodes that spanned 12 different contemporary groups of Angus calves (1992-2000) derived from a closed breeding population. FEC and blood pepsinogen measures were taken weekly over a 26-week period post-weaning, and the FEC data were Box-Cox transformed to normalize the distribution of phenotypes. These 305 test animals and more than 100 founding animals from the extended pedigree were genotyped across 190 microsatellites markers. The genome-wide analyses identified a suggestive genome-wide QTL on bovine chromosome (Chr) 8 (P < 0.002) and nominal QTL on Chr 4, 12 and 17 (P < 0.05). These findings were unique for cattle, and some corresponded to previously identified QTL locations for parasite-related traits in sheep to provide genome locations for further fine mapping of parasite resistance/susceptibility in Angus cattle.