Late-Breaking: Rumen microbiome composition and microbe network dynamics in beef cattle predict finishing performance under different backgrounding systems

Abstract Backgrounding (BKG) impacts growth and finishing performance in beef cattle. However, specific microbiome contributions to growth performance during this period, considering different BKG systems, remain unknown. A longitudinal study was designed to characterize the rumen microbiome and average daily gain (ADG) of Angus and Angus x Simmental calves (n = 38) placed under different BKG systems for 55 d after weaning: DL: a high roughage diet within a dry lot and CC: annual cover crop within a strip and PP, while a third group, PP: remained on perennial pasture vegetation within rotational paddocks, just as before weaning. After BKG, calves went to a feedlot for 142 d and finished with a high energy ration. Rumen bacterial communities were profiled by collecting fluid samples via oral probe, and sequencing the V4 region of the 16S rRNA bacterial gene, at weaning, during backgrounding and finishing. For calves moved to CC and DL BKG, bacterial composition diverged drastically, including sharp decreases in bacterial diversity (P < 0.001), while PP claves conserved more stable diversity patterns. During BKG, DL calves also showed the greatest ADG (P < 0.05), which coincided with increased abundance of taxa affiliated to the Aeromondales (Succinivibrio, Succcinimonas and Ruminobacter) (P < 0.001). However, once in the finishing phase, PP calves showed compensatory ADG, with significantly higher values, particularly compared with calves on DL BKG (v = 0.02). Network theory analyses were concordant with these patterns, highlighting the importance of understanding microbe-microbe interactions at early developmental stages to predict finishing performance. These results indicate that rumen microbes and their network interactions during backgrounding successfully predict finishing performance in beef cattle, underscoring the importance of early post weaning stages as potential targets for feeding interventions that can modulate the rumen microbiome to enhance lifelong animal performance.