A genome scan for quantitative trait loci for resistance to the gastrointestinal parasite 'Haemonchus contortus' in sheep

This paper presents some results from a genome scan for QTL affecting resistance to the gastrointestinal nematode Haemonchus contortus. The mapping flock comprised 571 sheep from four half-sib families, sired by individuals from the Golden Ram flock. The traits analysed were faecal egg counts after two artificial challenges at 6 and 13 months of age, termed FEC12 and FEC34 respectively. The correlation between these traits was low at 0.21. Animals were selectively genotyped for a total of 223 markers, and interval mapping performed on a within and across-family basis. For the within-family analysis 11 QTL (as chromosomal / family combinations) were significant at the 1% chromosome-wide (CW) level, with a further 18 significant at the 5% CW level. The allelic substitution effect (α) ranged from 0.19 to 0.50 phenotypic standard deviation units (σP). QTL significant at the 1%CW level were located on 9 different chromosomes, with only one of these regions significant for both FEC12 and FEC34. For the across-family analysis two chromosomal regions were significant at the 5%CW level, one each for FEC12 and FEC34.