Genome-Wide Association Study for Haemonchus contortus Resistance in Morada Nova Sheep

Abstract

Among the gastrointestinal nematodes affecting sheep, Haemonchus contortus is the most prevalent and virulent, resulting in health problems and production losses. Therefore, selecting sheep resistant to H. contortus is a suitable and sustainable strategy for controlling endoparasites in flocks. Here, 287 lambs of the native Brazilian Morada Nova hair sheep breed were subjected to two consecutive artificial infections with H. contortus and assessed for fecal egg count (FEC), packed cell volume (PCV), and live weight (LW). Forty-four animals ranked as having extreme resistance phenotypes were genotyped using the Illumina OvineSNP50v3 chip. A case–control genome-wide association study (GWAS) detected 37 significant (p < 0.001) markers in 12 ovine chromosomes in regions harboring quantitative trait loci (QTL) for FEC, Trichostrongylus spp. adults and larvae, weight, and fat; and candidate genes for immune responses, mucins, hematological parameters, homeostasis, and growth. Four single-nucleotide polymorphisms (SNP; OAR1_rs427671974, OAR2_rs419988472, OAR5_rs424070217, and OAR17_rs401006318) genotyped by qPCR followed by high-resolution melting (HRM) were associated with FEC and LW. Therefore, molecular markers detected by GWAS for H. contortus resistance in Morada Nova sheep may support animal selection programs aimed at controlling gastrointestinal nematode infections in flocks. Furthermore, genotyping of candidate genes using HRM qPCR may provide a rapid and efficient tool for animal identification.

Genomic Regions Associated with Resistance to Gastrointestinal Nematode Parasites in Sheep—A Review

“…2 "×" indicates a crossbreed study, and "," indicates several breeds used in the study. 3 H. contortus resistance, as defined by reference [40], is a phenotype measuring fecal egg count after artificial challenge with H. contortus, used to identify regions under selection for resistance to gastrointestinal nematodes. 4 H. contortus resistance, as defined by reference [38], is a phenotype obtained after ranking animals as extremely resistant or susceptible based on combined measurements of FEC, PCV, and live weight.…”

“…The OAR 2 was reviewed as a very prolific chromosome containing many genomic regions, genes, and QTLs that overlapped among several studies. Niciura et al [40] performed a case-control GWAS for FEC and PCV collected at 21, 28, 35, and 42 days after artificial infection of H. contortus following two rounds of infection in Morada Nova sheep. The integrin subunit α 6 (ITGA6) gene was found in a region associated with H. contortus resistance by Niciura et al [40] and with PLT by Berton et al [30].…”

“…Niciura et al [40] performed a case-control GWAS for FEC and PCV collected at 21, 28, 35, and 42 days after artificial infection of H. contortus following two rounds of infection in Morada Nova sheep. The integrin subunit α 6 (ITGA6) gene was found in a region associated with H. contortus resistance by Niciura et al [40] and with PLT by Berton et al [30]. This gene was also enriched (p < 0.05) in the gene ontology (GO) term "leukocyte migration" [30].…”

“…The range of results reported in the literature may be explained by several reasons: (i) resistance to gastrointestinal nematodes is a complex and polygenic trait with no major or singular gene contributing to the phenotype [40,41]; (ii) the type of methodology and statistical models used to identify regions associated with the trait vary among studies [1]; (iii) the type of markers used in the association analysis (50K SNP array-Ovine SNP50 array or 50K SNP BeadChip array, high-density array, customized SNP panel, whole genomic sequence, or microsatellites); (iv) the type of nematode infecting the animals (T. circumcincta, Trichostrongylus spp., H. contortus., or mixed species) [1,22]; (v) the type of infection (naturally exposed or artificially challenged); (vi) the different breeds used in the study, including resistant or susceptible genetically selected lines, and different cross experiments (backcross or F1) [1]; (vii) the different traits used to measure resistance (e.g., FAMACHA©, PCV, FEC, IgA or IgE levels, among others); (viii) the phase of the infection when the animals were evaluated; (ix) the age, sex, and physiological stage (pregnant, lactating, lamb) of the evaluated animals; (x) the size of the population and the number of animals with genotypic and phenotypic records; and (xi) the geographical location of the animal population.…”

Multi-omics elucidated parasite-host-microbiota interactions and resistance to Haemonchus contortus in sheep

“…These data were previously used for a case-control GWAS -genome-wide association study [44], but it was based on the Oar_v3.1 Texel reference genome. In the present study, the data from the 44 lambs were reanalyzed with the same reference genome used in the RNA-seq analysis.…”