Genome-Wide Association and Meta-Analysis in an Outbred Sheep Population: Identifying Genetic Loci Influencing Parasite Resistance

As a first step in identifying the genetic basis for parasite resistance in sheep, we performed a genome-wide association analysis in an outbred sheep population using sheep 50K SNP genotypes and two quantitative measurements: fecal egg counts (FEC) for Haemonchus contortus and packed cell volume (PCV), both taken at two time-points. The outbred population included 474 F2 lambs produced from five F1 sires. In order to combine the four genome-wide association results (PCV1, FEC1, PCV2 and FEC2), we conducted a meta-analysis which prioritized the significant SNP associations under a fixed-effect model which included sex, year of birth and age of lamb. A total of 2285 genome-wide significant SNPs associated with parasite resistant (p < 9.64E-05) were identified with this model. Strong associations (p < 5.91E-05) were found for 76 SNPs that were distributed on all autosomes but OAR8 and OAR21. Of the 24 ovine chromosomes, OAR6 and OAR23 at 38.04 Mb and 43.33 Mb, respectively, contained the most significant associations. This study should lead to the identification of genetic regions containing loci controlling parasite resistance in sheep.