Transcriptomic changes induced by controlled cyclical heat stress in the bovine mammary gland during lactation

This study examined the effects of heat stress (HS) on mid-lactating (100 ± 14 DIM) Holstein cows. Cows were assigned to either HS (temperature-humidity index [THI] 74-80; n = 7) or thermoneutral (pair-fed PFTN; THI 64; n = 8) conditions for 4 d. Exposure to HS reduced milk (4.34 ± 1.62 kg/d), protein (0.18 ± 0.04 kg/d), and fat (0.18 ± 0.05 kg/d) yields, highlighting the negative impacts of HS on production and homeostasis. To explore main molecular responses, mammary gland tissue samples were collected for transcriptomic analysis. Transcriptomic analysis revealed 54 upregulated and 74 downregulated genes in HS conditions. Upregulated genes included heat shock proteins (HSPA1A, HSPH1) and other stress-responsive genes (HSPA4L, SPINK4, ZNF772). Downregulated genes involved DNA repair (GADD45G and FEN1) and mitochondrial function (ND6 and ND5). Gene Ontology (GO) enrichment analysis indicated significant enrichment in protein quality control and stress response processes. Protein-protein interaction (PPI) of differentially expressed genes (DEG) analysis underscored networks of molecular chaperones and protein quality control pathways. Heat stress activates proteostasis-related pathways and molecular chaperone systems in the bovine mammary gland, reflecting cellular efforts to mitigate protein misfolding and maintain homeostasis.