The anthelmintic resistance of gastrointestinal nematodes (GINs) poses a significant threat to sheep worldwide, but genomic selection can serve as an alternative to the use of chemical treatment as a solution for parasitic infection. The objective of this study is to conduct genome-wide association studies (GWASs) to identify single nucleotide polymorphisms (SNPs) in Rambouillet (RA) and Dorper × White Dorper (DWD) lambs associated with the biological response to a GIN infection. All lambs were genotyped with a medium-density genomic panel with 40,598 markers used for analysis. Separate GWASs were conducted using fecal egg counts (FECs) from lambs (<1 year of age) that acquired their artificial infections via an oral inoculation of 10,000 Haemonchus contortus larvae (n = 145) or naturally while grazing on pasture (n = 184). A GWAS was also performed for packed cell volume (PCV) in artificially GIN-challenged lambs. A total of 26 SNPs exceeded significance and 21 SNPs were in or within 20 kb of genes such as SCUBE1, GALNT6, IGF1R, CAPZB and PTK2B. The ontology analysis of candidate genes signifies the importance of immune cell development, mucin production and cellular signaling for coagulation and wound healing following epithelial damage in the abomasal gastric pits via H. contortus during GIN infection in lambs. These results add to a growing body of the literature that promotes the use of genomic selection for increased sheep resistance to GINs.

Background/Objectives: Wool is an important product in sheep production, but the genetic mechanisms underpinning variation in wool growth are not fully understood. Identifying the genes and genomic variants that play a role in increasing fleece weight may allow for increased selection accuracy and improved economic return to producers. Methods: A genome-wide association study (GWAS) was conducted to investigate genetic associations with lifetime fleece weight, average fleece weight and average post-lambing ewe weight for Rambouillet, Polypay, Suffolk and Columbia ewes (N = 1125). Weir–Cockerham F_ST and runs of homozygosity (ROH) analyses were conducted to improve detection of putative wool-related signatures. Results: Twenty-four SNPs were identified through GWAS for lifetime fleece weight, average fleece weight and average post-lambing ewe weight. Chromosomes 2 and 6 contained ROH islands in Rambouillet, and chromosomes 2, 3 and 10 contained ROH islands in Suffolk. The F_ST analysis identified 18 SNPs in proximity to 37 genes of interest. Conclusions: Many of the SNPs and signatures of selection reported in this study are near or within current candidate genes for wool production and wool quality, including ADAR, KCNN3, NTN1, SETBP1, TP53 and TNFSF12. The significant SNPs implicated by GWAS may be used to predict ewes’ potential for lifetime wool production and are suggested as candidates for further study to continue to elucidate the genetic mechanisms underlying wool production traits in United States sheep breeds.