Exploring the Linkage Between Ruminal Microbial Communities on Postweaning and Finishing Diets and Their Relation to Residual Feed Intake in Beef Cattle.

Feed efficiency significantly impacts the economics of beef production and is influenced by biological and environmental factors. The rumen microbiota plays a crucial role in efficiency, with studies increasingly focused on its relationship with different rearing systems. This study analyzed 324 rumen samples from bulls and steers categorized as high and low efficiency based on residual feed intake. The animals were fed two diets (postweaning and finishing) and rumen samples were sequenced using a reduced representation sequencing (RRS) based approach. The results indicated that diet significantly affected microbial diversity and abundance. In postweaning diets, Actinomycetota, particularly , were prevalent, aiding carbohydrate fermentation. In contrast, was identified in finishing diets, likely contributing to acetate production. Additionally, and were abundant during postweaning, known for fiber degradation and volatile fatty acid production. Notably, and were associated with high feed intake and nutrient utilization, indicating their potential as microbial biomarkers. However, alpha diversity indices showed no significant relationship with feed efficiency, suggesting that diversity alone may not adequately reflect the complexity of feed efficiency phenotypes. These findings highlight the importance of diet and microbial interactions on feed efficiency and suggest further research to explore these microbial contributions to precision feeding strategies.