Nutritional Diarrhea Starts in the Rumen: Evidence for an Upper-gut Trigger of Lower-gut Dysbiosis
Nutritional diarrhea in dairy cows has traditionally been viewed through the results of hindgut dysfunction, neglecting the critical role of rumen microbiome. Our study breaks new ground by employing a compartment-resolved multi-omics approach to investigate how rumen and hindgut microbial communities collectively influence this condition. We reveal that diarrheic cows exhibit distinct microbial signatures in both gastrointestinal compartments: rumen Prevotella species with enhanced carbohydrate-degrading capacity drive excessive propionate production, while hindgut communities show decrease in beneficial Bifidobacterium and accumulation of opportunistic pathogens Alistipes. These changes correlate with key metabolic shifts, including reduced short-chain fatty acids in the hindgut and altered nitrogen metabolism. Our findings challenge the conventional hindgut-centric view of nutritional diarrhea, demonstrating instead a trans-compartmental disorder originating from rumen microbial imbalances. This work provides a new framework for developing targeted interventions that address both rumen and hindgut microbiota to improve dairy cow health and productivity.