PSV-12 - Microbial community structure of dairy cattle is stable through oscillating crude protein inclusion

Abstract: Diet plays an important role in shaping the structure of rumen microbial communities. However, little is known about the interaction between dietary crude protein (CP) level and CP feeding pattern on the rumen microbiome of dairy cows. Here the objective was to evaluate the influence of CP level (low protein [LP], 13.8%; high protein [HP], 15.5% of dry matter [DM] basis) and CP feeding pattern (OF = oscillating, SF = static) on the composition and diversity of the rumen microbiome of lactating dairy cows using 16S rRNA gene amplicon sequencing. Eight rumen-cannulated Holstein cows in mid to late lactation were assigned to a 2x2 factorial experiment consisting of 4 experimental periods of 28-d. Each experimental period had an adaptation phase to the diet (24 days) and a sampling phase (days 25-28). The treatments with oscillating feeding alternated diets every 48 h to vary CP above and below the mean CP level (OF-LP = 13.8 ± 1.8%; OF-HP = 15.5 ± 1.8% CP of DM) whereas diets were constant in the static feeding (SF-LP = 13.8%; SF-HP = 15.5% CP of DM). According to the NASEM (2021) model predictions the LP diet supplied 94% of the microbial protein requirement while the HP diet exceeded (104%) requirement. Rumen samples were collected 4 hours after feeding through a rumen cannula and amplicon libraries were generated targeting the V4 region of the 16S rRNA gene. The amplicon sequences were analyzed in qiime2. Sequences where trimmed based on their quality and then grouped in ASVs using DADA2. The ASVs were used to analyze the composition and diversity of the rumen microbiome in each treatment. Alpha diversity of the rumen microbiome did not change across treatments (Kruskal Wallis, p-value > 0.05), but Pielou's evenness increased by 0.01 units (Kruskal Wallis, p-value = 0.04). These results support the hypothesis that the rumen microbiome is stable to oscillating CP feeding patterns and compensates for the changes in crude protein content in the diet. Further research is required to understand the dynamics of this compensation and what other metabolic processes in the ruminant contribute to maintaining production under an oscillating diet.