A Comprehensive Genetic Study of Resistance to Nematodes in Sheep using the Ovine SNP Chip

Our aims were to: identify loci underlying variation in faecal egg count (FEC) both within and across sheep populations; evaluate the accuracy of genomic EBVs (GEBV) for FEC within and across populations; and explore non-additive genetic variation (i.e. epistasis and heterozygote advantage) for FEC. Data were available on 752 Scottish Blackface lambs, 2,371 Sarda-Lacaune backcross ewes, 1,000 Martinik Blackbelly-Romane backcross lambs and 64 Texel lambs. Phenotypes were FEC for Nematodirus and/or Strongyles at different ages. Several genomic regions of interest were identified, both within and across populations. Moreover, GEBV had moderate to good within-population predictive accuracy, whereas across-population predictions had accuracies close to zero. Epistasis analysis identified two pairwise SNP interactions significant at the suggestive level for Strongyles, and the heterozygote advantage analysis identified some SNPs reaching suggestive significance. Therefore, results suggest the presence a missing heritability undetectable via conventional GWAS, which warrants further exploration.