Genetics of nematode resistance in pasture-raised Central Anatolian Merino lambs

Gastrointestinal nematode infections are among the most economically significant health challenges in small ruminant production, particularly under extensive management systems. The genetic basis of host resistance offers a sustainable alternative to chemical control, which is increasingly limited due to rising anthelmintic resistance. In this study, we conducted a genome-wide association analysis (GWAS) to identify genomic regions associated with faecal egg count (FEC) as a proxy for nematode burden in 226 Central Anatolian Merino lambs raised on pasture. FEC exhibited moderate genomic heritability (h² = 0.22 ± 0.04), supporting the potential for genetic improvement. GWAS identified two SNPs that exceeded the genome-wide significance threshold and five additional loci at the chromosome-wide level. Notably, candidate genes including PLCL1, TCF7L2, ADRB1, GRIP1, VAC14, and TXNDC16 were located near significant SNPs. These genes are involved in immune signalling, epithelial barrier function, and redox regulation—mechanisms essential for helminth defence. Several regions overlapped with those previously reported for resistance to Eimeria and Moniezia spp., suggesting shared genetic pathways for gastrointestinal parasite resistance. These findings contribute to the understanding of the genetic architecture of nematode resistance and provide a foundation for the development of genomic selection strategies in native sheep breeds.