Effects of Left-Displaced Abomasum on the Rumen Microbiota of Dairy Cows

In this experiment, the rumen microbiota of healthy cows, cows with left-displaced abomasum (LDA), and cows after 7 days of LDA treatment (LDA_7) were compared to explore the correlation between LDA and the rumen microbiota and identify early warning markers for LDA. Compared with the healthy group and the LDA_7 group, the LDA group exhibited fewer Operational Taxonomic Units (LDA: 21,361; Healthy: 23,231; LDA_7: 23,956; <i>p</i> < 0.05). The results revealed significant differences in community structure between LDA-affected cows and healthy cows, as well as between treated and untreated LDA-affected cows. Specifically, the relative abundance of <i>Bacteroidota</i> significantly increased and the relative abundance of Firmicutes significantly decreased in LDA-affected cows (<i>p</i> < 0.05). At the genus level, the abundances of <i>UCG_002</i>, <i>UCG_010</i>, and <i>Bacteroidales_BS11_gut_group</i> significantly increased (<i>p</i> < 0.01), whereas those of <i>Trichosporon</i>, <i>Chryseomicrobium</i>, and <i>[Ruminococcus]_gauvreauii_group</i> significantly decreased in LDA-affected cows (<i>p</i> < 0.01). Functional prediction analysis indicated that amino acid biosynthesis and glycerol ester metabolism were significantly downregulated in LDA-affected cows (<i>p</i> < 0.01). After treatment, the abundance of key microbial taxa (<i>UCG_002</i> and <i>Lachnospira</i>) and metabolic functions normalized to levels similar to healthy cows (<i>p</i> > 0.05). These findings suggest that changes in rumen microbiota richness and diversity could serve as early warning markers for LDA detection.