This study was designed to identify genetically resistant animals to gastrointestinal nematode (GIN) infections using microsatellite polymorphisms of Ovar-DRB1 gene in Iranian Ghezel sheep breed lambs. In the present study 120 male Ghezel lambs were at 4 to 6 months of age randomly selected from six different sheep flocks in East Azerbaijan province (n=20 per flock). These lambs were naturally infected with GINs, and individual fecal samples were collected twice with a week interval to evaluate fecal egg counts (FEC). Blood samples were also collected for DNA isolation and PCR was performed to amplify the second exon and microsatellites within the second intron of the Ovar-DRB1 gene. The data were analyzed using a mixed modelof SAS software. The present study identified 24 genotypes and 20 alleles on Ovar-DRB1 gene. Results indicated that the presence of 510 bp (base pair) allele (called allele F) in both homozygote and heterozygote animals had a strong association (P<0.01) with lower FEC; while, presence of 506 bp allele (called allele E) in homozygote animals was significantly associated (P<0.01) with higher FEC. Thus, this study showed a strong association between microsatellite polymorphism of Ovar-DRB1 gene and resistance to GIN infections in Ghezel sheep lambs. تفاصيل المقالة