Single-step GWAS reveals candidate genes associated with longevity traits in Iranian Holstein cattle.

Longevity is a complex, polygenic trait of economic and welfare importance in dairy production. This study aimed to identify genomic regions and candidate genes associated with longevity traits-herd life (HL), productive life (PL), milking life (ML), and age at first insemination (AFI) in Iranian Holstein cattle using a single-step genome-wide association study (ssGWAS) based on pedigree, deregressed proofs, and genotypes from 150 cows (27,228 SNPs). At FDR < 0.05, 17 genome-wide significant SNPs were identified, three of which surpassed the Bonferroni threshold (p < 1 × 10⁻⁶); these mapped to 12 chromosomes (BTA5-BTA23), with the top windows explaining up to 2.8% of genetic variance. Functional annotation within ± 250 kb windows identified candidate genes including PDE7B, PRDX1, CDKN1B, and HMGA2, involved in cell cycle regulation, oxidative stress response, and energy metabolism. These findings provide exploratory insights into the genetic architecture of longevity in Iranian Holsteins, although validation in larger independent cohorts is required before marker integration into genomic selection.