Heat stress compromises nutritional quality and flavor of bovine raw milk: Evidence from multi-omics analyses

Heat stress is a growing concern for dairy production under global climate change. This study employed integrated multi-omics approaches to investigate how heat stress affects the antioxidant capacity, microbiota, metabolite profiles, lipid composition, and flavor compounds in raw milk. Results revealed that heat stress reduced antioxidant levels and altered the milk microbiome, favoring potentially spoilage-associated bacteria. Metabolomic analysis indicated disrupted energy, amino acid, and lipid metabolism, with reductions in beneficial unsaturated fatty acids, conjugated linoleic acid, and polar lipids such as phosphatidylcholine and sphingomyelin. Notably, several off-flavor volatiles, including hexanal, ketones, and sulfur compounds, increased in heat-stressed milk, while sweet esters declined. These compositional and sensory changes may compromise milk quality, nutritional value, and consumer acceptability. This study provides a comprehensive biochemical basis for understanding how heat stress affects milk quality, offering important references for quality assessment and risk monitoring in dairy production under warming climates.