Genomic Regions and Pathways Associated with Resistance to Gastrointestinal Parasites in Tropical Sheep Breed

The aim of this study was to estimate variance components and to identify genomic regions and pathways associated with resistance to gastrointestinal parasites, particularly Haemonchus contortus, in Santa Ines sheep, a Brazilian breed adapted to tropical climate. The degree of anemia assessed by the famacha card (FAM) and the egg counts per gram of feces (EPG) were evaluated to verify the resistance to gastrointestinal parasites. A total of 576 animals were genotyped using 12,785 SNPs of the Ovine SNP12k BeadChip (Illumina, Inc.). The variance components were estimated using a single trait model by single step genomic BLUP (ssGBLUP) procedure. The overall LD mean between marker pairs measured by r² was 0.23. Heritability estimates were low for EPG (0.11) and high for FAM (0.35). A total of 22 and 21 important windows for EPG and FAM traits were identified. The results of the enriched genes and functional grouping analyses showed that genes associated with FAM and OPG are involved in functions related to body's immune and defense response. The CCL28 gene located in OAR16 identified both for EPG and FAM acts as a chemotactic for CD4 and CD8 inactive T cells. The metabolic pathway involved in the CCL28 gene and in other genes associated with EPG and FAM, which are related to immunoglobulin synthesis in the intestine. The high heritability observed for FAM suggests that a good genetic progress should be possible in selective breeding programs for Santa Inês sheep besides the fact that the FAM are the most precise method to identify the infection by Haemonchus when compared to EPG. This study reported for the first time estimates of linkage disequilibrium between markers and genetic parameters for traits related to gastrointestinal parasites resistance in Santa Inês sheep breed.