Publication history: Accepted - 14 April 2022; Published - 3 May 2022.Estimated breeding values (EBV) for fecal egg counts (FEC) at 42–90 days of age (WFEC) and
91–150 days of age (PFEC) for 84 progeny-tested Katahdin sires were used to identify
associations of deregressed EBV with single-nucleotide polymorphisms (SNP) using 388,000
SNP with minor-allele frequencies ≥0.10 on an Illumina high-density ovine array. Associations
betweenmarkers and FEC EBVwere initially quantified by single-SNP linear regression. Effects
of linkage disequilibrium (LD) were minimized by assigning SNP to 2,535 consecutive 1-Mb
bins and focusing on the effect of the most significant SNP in each bin. Bonferroni correction
was used to define bin-based (BB) genome- and chromosome-wide significance. Six bins on
chromosome 5 achieved BB genome-wide significance for PFEC EBV, and three of those
SNP achieved chromosome-wide significance after Bonferroni correction based on the
14,530 total SNP on chromosome 5. These bins were nested within 12 consecutive bins
between 59 and 71 Mb on chromosome 5 that reached BB chromosome-wide significance.
The largest SNP effects were at 63, 67, and 70Mb, with LD among these SNP of r2 ≤ 0.2.
Regional heritability mapping (RHM) was then used to evaluate the ability of different genomic
regions to account for additive variance in FEC EBV. Chromosome-level RHM indicated that
one 500-SNP window between 65.9 and 69.9Mb accounted for significant variation in PFEC
EBV. Five additional 500-SNP windows between 59.3 and 71.6 Mb reached suggestive (p <
0.10) significance for PFEC EBV. Although previous studies rarely identified markers for
parasite resistance on chromosome 5, the IL12B gene at 68.5 Mbcodes for the p40 subunit of
both interleukins 12 and 23. Other immunoregulatory genes are also located in this region of
chromosome 5, providing opportunity for additive or associative effects.This research was funded by the USDA NIFA Organic
Agriculture Research and Extension Initiative grants no. 2016-
51300-25723 and 2010-51300-21641, and USDA Southern SARE
grant no. LS08-204