Microbial and Metabolomic Biomarkers of Feed Efficiency in Angus Cattle

In Tennessee and the United States, cattle account for a significant proportion of the livestock agricultural sector. In the beef cattle industry, 40-70% of the total cost of production comes from feed costs, resulting in billions of dollars going towards feeding cattle. Thus, identifying methods for improving feed efficiency is imperative for reduced feed input costs and more effective use of environmental and economic resources. The rumen microbiome contributes a vast amount of nutrients for the host ruminant, including approximately 70% of energy precursors as well as vitamins, proteins, and other nutrients. These microbes produce metabolites that are then available to the host and may influence host feed efficiency phenotypes. The microbiota and metabolites may be used as biomarkers of feed efficiency in beef cattle. In this dissertation, growing steers and heifers were used to identify potential biomarkers of feed efficiency using a residual feed intake (RFI) model of feed efficiency. In the steers, eight metabolites were greater in low-RFI steers compared to high-RFI steers (P ≤ 0.05) and unassigned protozoal taxa were present in greater abundance in high-RFI compared to low-RFI steers (P = 0.03). In the heifers, no metabolites differed by RFI (P > 0.05) after false discovery rate correction in the serum or rumen fluid. Furthermore, no microbial populations differed by RFI in the heifers, though several numerical differences did occur and were examined. In both the steers and heifers, rumen metabolites associated with nucleic and amino acid turnover appeared to be indicators of feed efficiency, though additional studies confirming this should be conducted. Additionally, the heifer study did not reach adequate statistical power to delineate differences in microbial populations after false discovery rate correction, but still may serve as biomarkers of feed efficiency because numerical differences were biologically relevant. Future studies should examine other sexes and production stages (primiparous and multiparous cows) to determine other microbial and metabolomic biomarkers of feed efficiency in beef cattle.