Characterization of rumen microbiota in lactating Holstein cows fed molasses versus corn grain at two levels of rumen degradable protein

Authors: GUDUK, ELIF - University Of Wisconsin; Hall, Mary Beth; Zanton, Geoffrey; STEINBERGER, ANDREW - University Of Wisconsin; WEIMER, PAUL - University Of Wisconsin; SUEN, GARRET - University Of Wisconsin; WEIGEL, K.A. - University Of Wisconsin

Submitted to: Frontiers in Microbiomes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2023
Publication Date: 8/14/2023
Citation: Guduk, E., Hall, M., Zanton, G.I., Steinberger, A.J., Weimer, P.J., Suen, G., Weigel, K.A. 2023. Characterization of rumen microbiota in lactating Holstein cows fed molasses versus corn grain at two levels of rumen degradable protein. Frontiers in Microbiomes. 2. Article 1204988. https://doi.org/10.3389/frmbi.2023.1204988.
DOI: https://doi.org/10.3389/frmbi.2023.1204988

Interpretive Summary: We investigated the impact of diets differing in nonfiber carbohydrates and level of rumen degradable protein (RDP) on changes in the ruminal bacterial populations of 12 lactating, ruminally cannulated Holstein cows. Three levels of molasses substituted for ground corn grain modified dietary carbohydrates by providing varying levels of sugar and starch, whereas 2 levels of soybean meal or expeller soybean meal were used to increase or decrease the amount of rumen degradable protein (RDP) in the diets. Ruminal liquid and solid digesta were analyzed to assess changes in the microbial profiles associated with changes in the diets. Dietary changes in RDP and carbohydrates altered the microbial profiles, causing increases or decreases in various genera of microbes. A number of microbial genera present in relatively low proportions showed strong correlations with ruminal fermentation products, suggesting that the predominant groups of microbes may not be the only ones of interest when evaluating microbes versus changes in fermentation product profile. Surprisingly, addition of more RDP to the diet reduced the richness and diversity of the bacterial community composition in rumen digesta liquid and solids. This work demonstrated that both dietary carbohydrate and protein can modify the rumen microbial communities in lactating dairy cows. Though further investigation is required, this may offer diets as tools to modify the rumen microbiome to achieve desired functionality and output of the rumen.

Technical Abstract: We investigated the impact of diets differing in nonfiber carbohydrates and level of rumen degradable protein (RDP) on changes in the ruminal bacterial populations of lactating Holstein cows. Twelve ruminally cannulated cows were randomly assigned to high or low RDP diets. Within each RDP level, molasses substituted for corn grain at 0, 5.25, or 10.5% of diet dry matter in a Latin square design. Samples of liquid and solids fractions of rumen digesta taken at the end of each period were analyzed and sequenced for the bacterial 16S rRNA gene, which was used to identify operational taxonomic units, with the liquid also analyzed for short chain fatty acids. Of the 30 genera with greatest relative abundance 26 differed (P < 0.05) by fraction, with genera in Bacteroidetes at greater abundance in solids and those in Firmicutes at greater abundance in liquid. Changes in protein degradability affected 6 genera, and 13 were affected by carbohydrates. Genera reported here will be those with >1% relative abundance. In liquid, relative abundance of Succiniclasticum decreased (P < 0.05) with increasing dietary molasses. However, in solids, relative abundance of CF231, YRC22, Clostridium, Desulfovibrio, BF311, and Oscillospira increased with molasses level. In the solids at higher vs. lower dietary RDP, Succiniclasticum increased and YRC22 and Pseudobutyrivibrio decreased (P < 0.05). Unexpectedly, although sucrose in molasses is soluble, effects of molasses on the genera in the liquid fraction were only negative, but primarily positive in solid fraction. Correlations between genera and fermentation products in the liquid showed genera of lower relative abundance,Shuttleworthia, Treponema, Lachnospira, and Schwartzia, to have strong positive correlations with molar proportions of propionate, butyrate and valerate and negative correlations with pH and acetate molar proportion. Interestingly, Fibrobacter showed positive correlation with lactate molar proportion. Butyrate molar proportion increased quadratically as molasses concentration increased (P = 0.017). Lactate molar proportion increased (P = 0.042) with more dietary RDP. No treatment effects were seen on pH, or propionate and valerate molar proportions, but a tendency for a quadratic effect of molasses treatment on molar proportion of acetate was noted.