Comparative analysis of heat stress response in Holstein Friesian and Sahiwal cattle through <scp>HSP70</scp> gene expression and promoter <scp>DNA</scp> methylation

This study investigated the heat stress response in Holstein Friesian and Sahiwal cattle by examining DNA methylation markers in the HSP70 gene promoter. Heat stress parameters such as temperature-humidity index (THI), average rectal temperature (ART), and heat tolerance coefficient (HTC) were analyzed alongside mRNA production during summer and winter. Blood samples were collected from both Holstein Friesian and Sahiwal cattle breeds to assess heat stress parameters, including THI, ART, and HTC. Seasonal variations in these heat stress parameters were evaluated along with mRNA expression levels. The DNA methylation pattern in the HSP70 gene promoter was assessed using the AvaI enzyme while gene expression was analyzed via quantitative PCR with PPIA as a control. Significant correlations were found between seasons, breed-specific heat stress parameters, HSP70 expression, and DNA methylation. Both Sahiwal and Holstein Friesian cattle exhibited higher HTC when DNA methylation was absent, with Sahiwal cattle consistently demonstrating greater heat tolerance than Holstein Friesians. This study highlights the complex interplay between seasonal changes, breed-specific adaptations, and epigenetic modifications in cattle's heat stress responses. The upregulated HSP70 expression suggests a role in thermotolerance. However, the study focused on a single DNA methylation change; broader investigations into additional epigenetic modifications are needed to fully understand heat stress resilience mechanisms across cattle populations.