Monensin Alters the Functional and Metabolomic Profile of Rumen Microbiota in Beef Cattle

Abstract

To identify differences in rumen function as a result of feeding monensin to beef cattle, rumen fluid metagenomics and metabolomics analyses were used to evaluate the functional attributes and metabolites of rumen microbiota in beef steers fed no or 200 mg/d of monensin. Eight rumen-fistulated steers were used in the study for a period of 53 days. Rumen fluid samples were collected on the last day of the experiment. Monensin increased the relative abundance of Selenomonas sp. ND2010, Prevotella dentalis, Hallella seregens, Parabacteroides distasonis, Propionispira raffinosivorans, and Prevotella brevis, but reduced the relative abundance of Robinsoniella sp. KNHs210, Butyrivibrio proteoclasticus, Clostridium botulinum, Clostridium symbiosum, Burkholderia sp. LMG29324, and Clostridium butyricum. Monensin increased the relative abundance of functional genes involved in amino acid metabolism and lipid metabolism. A total of 245 metabolites were identified. Thirty-one metabolites were found to be differentially expressed. Pathway analysis of the differentially expressed metabolites revealed upregulated metabolic pathways associated with metabolism of linoleic acid and some amino acids. These findings confirm that monensin affects rumen fermentation of forage-fed beef cattle by modulating the rumen microbiome, and by reducing amino acid degradation and biohydrogenation of linoleic acid in the rumen.

Keywords: beef cattle; metabolomics; metagenomics; monensin; rumen fluid.

Figure 1

Linear discriminant analysis effect size (LEfSe) of rumen microbiota of beef steer fed no (control) or 200 mg/d of monensin. The linear discriminant analysis plot indicates the most differentially abundant taxa found by ranking according to their effect size (≥2.0) at the genus (A) and species level (B). The taxa enriched in steers fed the control diet are indicated with a positive score (green), and taxa enriched by the monensin treatment have a negative score (red). Only taxa meeting the significant threshold of 2.0 are shown.

Figure 2

(A) Distribution of category of the predicted genes by KEGG. (B) Differential KEGG gene functions. Differences between control and monensin samples were tested for significance using a Mann Whitney test (p ≤ 0.05).

Figure 3

Relative abundance of the category of carbohydrate-active enzymes according to carbohydrate-active enzyme (CAZy) database. AA = Auxilliary Activities, CBM = Carbohydrate Binding Modules, CE = Carbohydrate Esterases, GH = Glycoside Hydrolases, GT = Glycosyl Transferases, PL = Polysaccharide Lyases.

Figure 4

(A) The scores plot of PCA model showing the directions that best explain the variance between the two treatments. (B) OPLS-DA score plot of all metabolite features. Group 1 = steers fed Control diet, Group 2 = steers fed 200 mg d⁻¹ of monensin. One data point represents one composite rumen fluid sample of each steer.