Genome-wide association study identifies major histocompatibility complex genes linked to resistance to gastrointestinal nematodes in grazing Rideau Arcott sheep

Gastrointestinal nematodes (GINs) can infect grazing sheep, reducing animal health and welfare, resulting in substantial economic losses due to decreased production and increased animal mortality. This study aimed to identify single nucleotide polymorphisms (SNPs) significantly associated with resistance against GIN in grazing Arcott Rideau sheep in Ontario and explore annotated genes and quantitative trait loci (QTLs) that may influence resistance to GIN infection. Estimated breeding values for fecal egg count records collected from sheep aged 13 to 19 months that were naturally exposed to GIN while grazing were de-regressed and used as pseudo-phenotypes in the genome-wide association analyses. Genes and QTLs were annotated within 100 kb base pairs upstream and downstream of each significant SNP. A total of 58 significant SNPs were found, and 138 genes and 31 QTL were annotated. The BTNL2, Ovar-DRA, and TNXB genes, belonging to the major histocompatibility complex, were identified on chromosome 20. These genes are involved in different immune system processes, including wound healing, inflammatory response, and T-cell regulation. Three QTLs previously identified as related to resistance to GIN in sheep were also identified, reinforcing the association of the identified genomic regions with sheep's resistance to GIN infection.