Abstract
We investigated the rumen microbiome of Angus bulls selected for Residual Feed Intake-Expected Progeny Difference (RFI-EPD) utilizing deep shotgun metagenomic sequencing. Negative RFI-EPD bulls (NegRFI: n = 10; RFI-EPD = -0.3883 kg/d) and Positive RFI-EPD bulls (PosRFI: n = 10; RFI-EPD = 0.2935 kg/d) were selected from a group of 59 Angus bulls [average body weight (BW) = 427.81 ± 18.77 kg] fed a high-forage total mixed ration after a 59-d testing period. At the end of the 59-d period, rumen fluid samples were collected for bacterial DNA extraction and subsequent shotgun metagenomic sequencing. Results of the metagenome analysis revealed greater gene richness in NegRFI bulls compared with PosRFI. Analysis of similarity revealed a significant difference (P = 0.05) in the rumen microbial community between the NegRFI and PosRFI. Linear Discriminant Analysis effect size (Lefse) was used to identify the differentially abundant taxa. The Lefse results showed that class Fibrobacteria (LDA = 5.1) and genus Fibrobacter (LDA = 4.8) were the most differentially enriched markers in NegRFI bulls, compared with PosRFI bulls. Relative abundance of the carbohydrate-active enzymes was also compared using lefse analysis. The results showed greater relative abundance of glycoside hydrolases and carbohydrate-binding modules such as GH5, CBM86, CBM35, GH43, and CBM6 (LDA > 3.0) in NegRFI bulls whereas GH13 and GT2 were greater in PosRFI. The distinct metabolic and microbial profiles observed in NegRFI, compared with PosRFI bulls, characterized by greater gene richness and specific taxa such as Fibrobacter, and variations in carbohydrate-active enzymes, underscore the potential genetic and functional differences in their rumen microbiome. These findings contribute to a deeper understanding of the interplay between host genetics, microbiota, and feed efficiency in Angus bulls, opening avenues for targeted interventions and advancements in livestock management practices.