Dietary baicalin supplementation increases the milk unsaturated fatty acid proportion through modulating milk metabolism and the microbiome in dairy cows.

The composition and characteristics of milk fatty acids, which play a pivotal role in nutrition, are profoundly influenced by the dietary components consumed by cows. Like other flavonoids, baicalin (BAI) may affect the proportion of milk fatty acids. This study evaluates the effect of dietary supplementation with BAI on milk microbiota and host metabolism to modulate milk fatty acid composition. Results indicated that dietary supplementation with BAI increased proportions of unsaturated fatty acids (UFAs) (e.g., C18:1n9c and C18:2n6c). BAI reshaped the milk microbiome, wherein enriched taxa such as Myroides were positively associated with increased milk UFA and altered milk metabolite profiles. Additionally, BAI regulated some metabolites (e.g., alpha-KG) in milk, which were linked to promoting the synthesis of UFA, and regulated host metabolism (e.g., primary bile acid biosynthesis) that enhanced UFA metabolism. Together, these findings demonstrate the great potential of BAI in effectively modifying the milk fatty acid profile to enhance its nutritional quality.IMPORTANCEMilk is a major source of dietary fat for humans, and increasing the proportion of unsaturated fatty acids (UFAs) in milk can improve its nutritional quality. This study demonstrates that dietary supplementation with baicalin, a natural flavonoid from Scutellaria baicalensis, effectively increases milk UFA content in dairy cows. The findings reveal that baicalin modulates milk fatty acid composition through reshaping the milk microbiome (e.g., enriching Myroides) and altering mammary and systemic metabolism. These results provide a novel, plant-based nutritional strategy for enhancing milk quality and offer mechanistic insights into the interplay between dietary bioactive compounds, mammary microbiota, and lipid metabolism in lactating dairy cows.