98 Award Talk: Exploring the ruminal microbiome of beef cattle with divergent feed efficiency.

Abstract As the livestock industry intensifies efforts to improve productivity while reducing environmental impact, feed efficiency has become increasingly vital in cultivating sustainable beef production. To guide selection for feed-efficient beef cattle generationally, genetic prediction tools such as Feed Efficiency-Expected Progeny Differences (FE-EPDs) are widely used. Traditionally, the selection for feed efficiency has focused on phenotypic indicators—such as feed intake or average daily gain—yet growing evidence highlights the rumen microbiome as a key biological contributor to variation in feed utilization. This presentation explores the intricate relationship between the rumen microbial ecosystem and the selection for feed efficiency in beef cattle, with the goal of identifying microbial signatures and functional differences that can enhance the selection for feed-efficient cattle. Our research integrates microbial ecology with performance and genetic data to investigate the taxonomic and functional role of the rumen microbiome in commercial beef systems. Through 16S rRNA sequencing and deep-shotgun metagenomic analysis of rumen samples collected from a diverse cohort of bulls, we characterized microbial taxa and functional gene pathways associated with residual feed intake (RFI) and other efficiency-related traits. Preliminary analyses using 16s rRNA Gene sequencing revealed distinct microbial taxonomic profiles associated with variation in feed efficiency. Notably, microbial communities enriched in fiber-degrading bacteria favoring propionate production, a key volatile fatty acid (VFA) important in supporting metabolizable energy production in cattle, were enriched in our feed efficient bulls, compared to their inefficient counterparts. To underscore the functional and gene annotation of the rumen microbiome, shotgun metagenomic profiling was conducted and revealed key differences in microbial functional potential between divergently selected RFI-EPD bulls, particularly within carbohydrate-active enzyme (CAZy) families. Feed efficient bulls showed greater relative abundances of genes coding for glycoside hydrolases and carbohydrate-binding modules, suggesting a microbiome more capable of breaking down complex plant polysaccharides. These enzymes enhance fiber digestion, VFA production, and nutrient extraction; furthermore, aligning with improved feed efficiency and highlighting the potential for CAZy profiles to serve as biomarkers for microbiome-driven performance variation in beef cattle. These findings underscore the potential of integrating rumen microbiome-driven selection strategies into the beef production industry. Incorporating microbiome-informed metrics alongside feed efficiency-EPDs could improve the precision of selecting feed-efficient cattle and support more sustainable beef production systems.