Abstract
Climate change poses an increasing challenge to livestock production, making the identification of thermally resilient breeds crucial. This study investigated the expression patterns of eight thermal stress-related genes (HSP90AA1, HSPA8, HSPA1A, IL-6, IL-10, TNF-α, NOS-3, and SOD-2) in two strains of indigenous Pramenka sheep (Hercegovačka and Dubska) under different climatic conditions. Blood samples were collected from 96 sheep across four locations during summer and winter seasons. Gene expression was analyzed using RT-PCR and evaluated against comprehensive environmental data, including the temperature-humidity index (THI). Principal component analysis revealed distinct gene expression patterns between strains and seasons. The Hercegovačka strain showed consistently higher expression of HSP90AA1 compared to the Dubska strain in both seasons (summer: 5.81 vs. 2.47; winter: 4.38 vs. 1.19, p < 0.05), with all individuals exhibiting upregulation during summer and 95.8% showing upregulation during winter. Both strains demonstrated reduced expression of pro-inflammatory cytokines (IL-6, TNF-α) and increased expression of anti-inflammatory IL-10, suggesting maintained immunocompetence under thermal stress. The expression patterns of oxidative stress-related genes (SOD-2, NOS-3) indicated effective management of oxidative stress in both strains. These results suggest superior thermal adaptation in the Hercegovačka strain, particularly through HSP-mediated cellular protection mechanisms, while both strains show favorable immune and oxidative stress responses. These findings provide valuable insights for climate-resilient sheep breeding programs and the conservation of adaptive genetic resources.