Heat stress induced enrichment of Klebsiella pneumoniae links mammary microbiota dysbiosis with inflammatory responses

Heat stress reduces milk yield in dairy cows, and this decline cannot be fully explained by decreased feed intake. Using heat-stressed and pair-fed cows, we combined proteomics, metagenomics, and in vitro assays to examine mammary inflammation. Heat stress suppressed metabolic pathways, increased inflammatory markers, disrupted mammary microbial balance, and enriched Klebsiella pneumoniae, which was positively associated with elevated somatic cell scores. This bacterium directly induced inflammatory and apoptotic responses in bovine mammary epithelial cells. These findings identify a microbiota-mediated pathway linking heat stress to subclinical mammary inflammation and milk loss, providing new insight for protecting mammary health under climate stress.