Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2017
Publication Date: 6/6/2017
Publication URL: http://handle.nal.usda.gov/10113/5700739
Citation: Artegoitia, V.M., Foote, A.P., Lewis, R.M., Freetly, H.C. 2017. Rumen fluid metabolomics analysis associated with feed efficiency on crossbred steers. Scientific Reports. 7:2864. doi:10.1038/s41598-017-02856-0.

Interpretive Summary: Improving production efficiency of cattle by increasing beef produced per amount of feed offered would result in economic and environmental benefits. Digestion and nutrient absorption is considered one of the most important source of variation in cattle growth efficiency. Hence, differences in feed efficiency might be related to changes in the chemical profile in the cattle stomach (rumen). We characterized, for the first time, chemical changes in the rumen using a distinct ruminal profiling method, identifying 33 biomarkers related to differences in feed efficiency. The fatty acid metabolism (linoleic and alpha-linolenic) and synthesis of proteins (aromatic amino acid), were the most altered mechanism associated with feed efficiency. The combination of ruminal pentadecanoic acid, plamitic acid, linoleic acid and alpha-linolenic acid, and the combination of plasma arachidonic:docahexanoic ratio and alpha-linolenic acid, were able to distinguish lower and higher feed efficiency animals in rumen and blood, respectively. Particularly, blood fatty acid profiles as a candidate biomarker have the potential as an accessible and useful predictive tool to understand the mechanism of feed efficiency. In addition, the "snapshot" profile of rumen fluid, which associated the levels of fatty acids and proteins with lactic acid, suggest that the balance between microbial population and ruminal absorption of organic acids affect the production efficiency of crossbreed beef steers. Such information could usefully contribute to selection decisions.

Technical Abstract: The rumen has a central role in the efficiency of digestion in ruminants. To identify potential differences in rumen function that lead to differences in feed efficiency, rumen fluid metabolomic analysis by LC-MS and multivariate/univariate statistical analysis were used to identify differences in rumen metabolites. Individual feed intake and body-weight was measured on 144 steers for 105 d on a high concentrate ration. Eight steers with the greatest average daily gain (ADG) and 8 steers with the least ADG without difference in dry matter intake were selected. Blood and rumen fluid was collected 26 d before slaughter and at slaughter, respectively. Metabolomics analysis of rumen fluid identified 33 potential biomarkers for feed efficiency based on t-test, fold changes and partial least square discriminant analysis These metabolites were primarily involved in linoleic and alpha-linolenic metabolism (impact-value 1.0 and 0.75, respectively; P < 0.05); both pathways were down-regulated in the greatest-ADG compared with least-ADG group. The fatty acids identified as potential biomarkers were quantified in rumen and plasma using targeted MS to validate and evaluate the simple combination of metabolites that effectively predict feed efficiency. Furthermore, the integrated pathway analysis, provided a new comprehensive insight into ruminal biochemical changes of feed efficiency.