Identification of Candidate Genes Associated with Eimeria spp. Oocyst Load in Central Anatolian Merino Sheep

Coccidiosis caused by Eimeria spp. is a significant protozoal disease impacting the health and productivity of sheep and other livestock species. Host resistance to coccidiosis exhibits considerable individual variation, suggesting a genetic basis for susceptibility and resilience. This study aimed to identify genomic regions associated with oocyst load of Eimeria spp. in sheep using a genome-wide association study (GWAS) approach. A total of 226 sheep were phenotyped for oocyst counts using a standardized flotation technique. Genotyping was performed using a 50 K high-density SNP array. Quality control measures included filtering for minor allele frequency, call rate, and Hardy-Weinberg equilibrium. GWAS analysis was conducted using a mixed linear model accounting for relatedness among individuals. Significant associations were identified on chromosomes 1, 8 and 20. Candidate genes mapped to these regions included PARK2, PACRG, QKI, PDE10A, RAB44, and CDKN1A, which are involved in mitochondrial quality control, cellular stress response, immune modulation, and epithelial integrity maintenance. These biological functions are critical for host defence mechanisms against protozoal infections such as coccidiosis. This study reveals novel candidate genes and biological pathways potentially influencing coccidial oocyst load in sheep. These findings contribute to the understanding of host genetic resistance to Eimeria infections and may inform future breeding strategies in sheep.