180 Identification of rumen microbiome and metabolome profiles in Angus bulls differing in residual feed intake classification.

Abstract Improving livestock feed efficiency enhances availability of high-value products, increases producer’s profitability, and progresses sustainability. Feed efficiency is a complex phenotype influenced by interactions between the host animal and its microbiome. To unveil this complexity, the current study aimed to comprehensively characterize rumen fluid from Angus bulls differing in residual feed intake (RFI) classification by utilizing a large sample size and a multi-omics approach. Rumen samples (n = 1,176) were collected from Angus bulls held at eight feed testing centers located in Georgia, Iowa, California, Nebraska, Montana, and West Virginia. Two testing centers were visited twice, resulting in 10 different contemporary groups. All animals were rank ordered by RFI, determined by individual feed intake and performance data obtained from the testing centers. Animals were then classified into High- (n = 294), Medium- (n = 588), and Low-RFI (n = 294) groups based on interquartile range. Upon sample collection, DNA extraction and 16S rRNA sequencing were performed on all samples. A subset of ruminal samples from High- (n = 60) and Low-RFI (n = 60) animals were chosen for untargeted ultra-performance liquid chromatography–mass spectrometry metabolomic analysis. A mixed-effects model was used to analyze the individual microbial taxa and alpha diversity indexes. For the metabolomics data, a multivariate analysis was performed, and the biomarkers were selected based on their Variable Importance in Projection (VIP > 1.5). No differences (P > 0.19) were detected between RFI classification for alpha diversity. At the genus level, 88 taxa were significantly (P ≤ 0.05) associated with RFI classification. Out of those, Aereimonas_A_501548, Anaerosalibacter, Frederiksenia, and Taonella were more abundant in High-RFI bulls (P < 0.04) when compared to Low-RFI, and neither differed from Medium-RFI. Conversely, RUG14515, Alkalibacter, Fretibacterium, and ER4 were more abundant in Low-RFI bulls (P < 0.03) when compared to High-RFI, and neither differed from Medium-RFI. All taxa mentioned had a relative abundance less than 0.2%, indicating that bulls utilized in the study had similar core microbiomes, and less-abundant taxa were more associated with feed efficiency. Rumen metabolomic analysis revealed that 17 pathways were differently expressed (P < 0.01) in Low- versus High-RFI bulls. Notably, arachidonic acid metabolism, beta-alanine metabolism, biosynthesis of unsaturated fatty acids, cysteine and methionine metabolism, glutathione metabolism, steroid biosynthesis, and valine, leucine and isoleucine biosynthesis were all impacted by bull RFI status. Collectively, these findings show that bulls with different RFI classifications have different microbial taxa and metabolic profiles in their rumen, highlighting the importance of the host-microbiome interaction on feed efficiency.