PSVI-6 Genomic determinants of the rumen microbiome and metabolome in Angus steers

The rumen microbiome provides approximately 70% of energy required for the ruminant host through fermentation byproducts. Due to microbial impacts on host health and productivity, several studies have associated microbiome and metabolome variation with important sustainability phenotypes, such as feed efficiency and methane emissions. Recent studies have indicated the microbial communities present in rumen fluid are under low-to-moderate host genetic control. However, microorganisms present on the rumen wall have been underrepresented in research, negating their unique role in host-microbiome interactions. Current studies investigating heritability of the rumen planktonic microorganisms are plagued by small sample sizes, high management and breed heterogeneity, and low resolution for classifying microbial communities. To determine the heritability of the rumen fluid and epithelium-associated microbiome and metabolome, Angus steers (n = 350) were enrolled in a 70-d feed efficiency trial, where real-time dry matter intake was measured. Body weights were collected throughout the trial to calculate average daily gain and residual feed intake. Mid-trial, a novel surgery method was used to swab the rumen wall to capture epithelium-associated microorganisms. On d 70, 50 mL of rumen fluid was obtained from steers using orogastric tubing for collection of planktonic microbial communities. Metagenomic DNA extracted from both rumen fluid and epimural samples was used for reduced representation sequencing to predict microbial features such as diversity, composition, and putative function. Genomic DNA isolated from whole blood was used to perform low-pass whole genome sequencing for use in downstream heritability estimates and variant association analyses. Many core microbial abundances are under low-to-moderate host genetic control (h2 > 0.15; P < 0.05); however, many microorganisms had low heritability estimates (h2 < 0.10). Preliminary genome-wide associations studies are vastly underpowered to detect host genetic variants associated with microbial features, but data generated using the total number of animals will better refine these polymorphisms. Several key heritable metabolites were identified in amino acid metabolism pathways in rumen fluid (P < 0.05). The rumen microbiome appears to act as a complex polygenic trait and incorporating microbial features into prediction models may improve feed efficiency estimations. Understanding host genetic control of the rumen microbiome and metabolome may empower downstream applications to enhance genomic and phenotypic predictions for feed efficiency and other sustainability traits in beef cattle.