Bacterial and Fungal Dynamics of the Uterine Microbiota in Postpartum Beef Cows Supplemented with Grape Pomace

The bovine uterus, once considered sterile, is now recognized as a dynamic microbial ecosystem that undergoes substantial changes during the postpartum period and plays a critical role in reproductive health. This study investigated the composition and temporal dynamics of the uterine bacterial and fungal microbiota in postpartum Angus cows and showed that dietary grape pomace bolus supplementation was associated with temporal shifts in microbial community composition, including changes in selected bacterial taxa and increased fungal community stability. A total of 19 cows were allocated to control (n = 10) or treatment groups (n = 9), with treated animals receiving slow-release grape pomace boluses administered every three weeks from 21 days prepartum until 60-70 days postpartum. Uterine lavage samples were collected during the first (days 4-12) and ninth (days 63-70) postpartum weeks and analyzed using amplicon-based sequencing targeting the bacterial 16S rRNA (V3-V4) region and the fungal ITS2 region. The uterine microbiota exhibited pronounced temporal changes, with Firmicutes predominating in the early postpartum period and an increased abundance of potentially pathogenic Fusobacteria and Bacteroidetes observed by week nine postpartum, particularly in control cows. Grape pomace supplementation was associated with a more favorable bacterial profile, including a reduced relative abundance of key uterine pathogens such as Fusobacterium necrophorum and Trueperella pyogenes. The uterine mycobiome was dominated by Ascomycota across all groups; however, supplemented cows showed greater fungal community stability and a lower prevalence of opportunistic genera, including Candida spp. In conclusion, dietary grape pomace supplementation may beneficially modulate both bacterial and fungal uterine microbiota during the postpartum period, suggesting its potential as a natural strategy to support uterine microbial homeostasis and reproductive health in beef cows.