Abstract
Abstract Gastrointestinal nematodes (GIN) are detrimental to the health and productivity of sheep across the world, necessitating genetic selection for improved GIN resistance. In this study, we used genomic analyses across- and within- two important breeds in the United States (US), Rambouillet and Dorper, to investigate physiological mechanisms associated with GIN resistance. Genomic data were evaluated from two experiments where lambs were challenged with GIN, either in a natural environment or artificially. Lambs were genotyped with the Axiom™ Ovine Genotyping Array (50K) with 42,608 single nucleotide polymorphisms (SNP) remaining following quality control for minor allele frequency and variant call rate. In experiment 1, a fecal egg count (FEC) was collected from four- to eight-month-old Dorper and Rambouillet lambs (n=188 total) exposed to GIN on pasture. Using Plink v1.9, a genome-wide association study (GWAS) identified significant SNP (P < 6.0e-5) associated with either an increase or decrease of FEC on chromosomes 1, 2, 3, 4, 12, 15 and 20. In Experiment 2, Rambouillet lambs (n=77) were inoculated with 10,000 Haemonchus contortus L3 larvae and FEC and packed-cell volume (PCV) were recorded. An ensuing GWAS identified significant SNP (P < 2.0e-5) on chromosomes 1, 2, 3, 5, 7, 16, 17 and 23 associated with high and low FEC and SNP on chromosome 10 associated with decreased PCV. Multiple genes were in proximity to the identified SNP, including PIK3 subunits in both experiments. Pathway analysis of reported genes, including PIK3, IMP4, NDST3, MRPL22, HSPA2, TGFA, TGFBR1 and RUNX1 revealed involvement in tissue repair, T-cell differentiation and cytokine signaling in Rambouillet and Dorper sheep more resistant to GIN. Results from this study contribute to the genetic underpinnings of host response to GIN in two important breeds in the US, providing a foundation for future selection of animals more resistant to H. contortus infection.
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