Temporal Modulation of Duodenal Microbiota in Dairy Cows: Effects of Dietary Shift from High Forage to High Concentration

The duodenum and its resident microbiota play crucial roles in nutrient digestion and absorption. However, the temporal dynamics of duodenal microbiota in response to different dietary regimes remain poorly understood. The aim of the present study was to explore the effects of high-forage (HF) and high-concentration (HS) diets on the circadian rhythm variation of duodenal fermentation and microbial communities in dairy cattle. Six duodenum-cannulated Holstein dairy cows were assigned to HF and HS diets according to crossover design with two periods, and each period included 21d (18 d for adaptation, 3 d for sampling). Duodenal content samples were collected at six time points (07:00, 11:00, 15:00, 19:00, 23:00, and 03:00) for VFA analysis and microbial characterization. The times of 11:00, 15:00, and 19:00 recorded as the light phase and 23:00, 03:00 and 07:00 being the dark phase. Results showed that TVFA displayed a significant circadian rhythm after the HS diet introduction (p < 0.01). The concentration of TVFA (p < 0.01) and acetate (p < 0.01) concentrations were significantly higher during light than dark phase regardless of diet type. PERMANOVA analysis revealed that diet and diet-time interaction strongly influenced the composition of duodenal microbiota. The relative abundance of Lachnospiraceae_ND3007_group showed a positive correlation with the propionate proportions under the HS diet during the light phase, while the HS diet significantly increased the abundance of Bifidobacterium and norank_f__Lachnospiraceae. These findings provide novel insights into diet-dependent circadian regulation of duodenal fermentation in dairy cattle.