The effects of feeding rations that differ in neutral detergent fiber and starch within a day on the daily pattern of key rumen microbial populations.

The effect of feeding a single TMR versus multiple rations across the day that differ in concentrations of neutral detergent fiber (NDF) and starch on the daily pattern of rumen microbial populations was characterized. Diets included a control total mixed ration (CON; 33.3% NDF), a low-fiber diet (LF; 29.6% NDF), and a high-fiber diet (HF; 34.8% NDF). Nine cannulated Holstein cows were assigned to 1 of 3 treatment sequences in a 3 × 3 Latin square design. Treatments included feeding CON ad libitum at 0900 h, feeding HF at 70% of daily offering at 0900 h and LF at 30% of daily offering at 2200 h (H/L), and feeding LF at 30% of daily offering at 0900 h and HF at 70% of daily offering at 1300 h (L/H). Rumen digesta was collected to represent every 3 h across the day, microbial DNA was extracted, and real-time quantitative PCR was used to determine the relative abundances of total bacteria, total fungi, total protozoa, , , , , , , , and . The relative abundances of total bacteria, total ciliated protozoa, , , , , and were affected by time of day. Additionally, treatment affected the relative abundance of certain microbial groups at specific times of day. Notably, H/L treatment dramatically increased the relative abundances of , , and at 0900 h, by 2.5-, 5.4-, and 4.4-fold, respectively. Furthermore, the relative abundances of (3.9-fold), (3.9-fold), (1.3-fold), (1.3-fold), and (4.5-fold) were greatly increased by L/H at 0900 h. At 0600 h, the relative abundance of was 58% greater in L/H than H/L and the relative abundance of was 49% greater in H/L than L/H. Results suggest that there is a daily pattern of selected microbial populations that is altered by feeding rations that differ in NDF and starch within a day, with the greatest difference occurring before morning feeding.