| Summary: | This study aimed to determine changes and interactions of ruminal microbiota and chemical parameters in dairy cows fed FTMR. Twelve multiparous Holstein dairy cows (Body weight = 616 ± 13.4 kg; day in milk = 106 ± 7.55 d; and parity = 2.31 ± 0.49; mean ± standard deviation) were divided randomly into two treatments depending on the day in milk, milk production, and parity. The two treatments were: (1) total mixed ration (TMR) and (2) FTMR. Illumina MiSeq sequencing was used to explore the changes in the ruminal microbiota. The results revealed that the bacterial and fungal diversity of the FTMR group were significantly higher than the TMR group. The predominant microbiota phyla in the bacteria and fungi showed significant differences between TMR and FTMR, as follows: <i>Verrucomicrobia</i> (<i>p</i> = 0.03) and <i>Tenericutes</i> (<i>p</i> = 0.01), <i>Ascomycota</i> (<i>p</i> = 0.04) and <i>Basidiomycota</i> (<i>p</i> = 0.04). The dominant bacterial genera in the bacteria, fungi, protozoan, and archaea that showed significant differences between TMR and FTMR were Unclassified_<i>Bacteroidales</i> (<i>p</i> = 0.02), Unclassified_RFP12 (<i>p</i> = 0.03), <i>Candida</i> (<i>p</i> = 0.0005), <i>Bullera</i> (<i>p</i> = 0.002), <i>Cryptococcus</i> (<i>p</i> = 0.007), and <i>Ostracodinium</i> (<i>p</i> = 0.01). LefSe analysis was performed to reveal the biomarker genera of the rumen microbiota community (bacteria, fungi, protozoan, and archaea) in the TMR and FTMR were the genera <i>Shuttleworthia</i>, <i>Ruminococcus, Cryptococcus</i>, <i>Mycosphaerella</i>, <i>Bullera</i>, <i>Candida</i>, and <i>Ostracodinium</i>. NH<sub>3</sub>-N concentration (<i>p</i> < 0.0001), total VFA concentration (<i>p</i> = 0.003), and molar proportion in total VFA of acetate (<i>p</i> = 0.01) were higher for the cows fed FTMR compared with the cows fed the TMR. Several bacterial genera showed significant correlations with rumen fermentation parameters. The genus Unclassified_<i>Bacteroidales</i> and <i>Bullera</i> were positively correlated with total volatile fatty acids (VFA) and acetate, whereas <i>Candida</i> and <i>Ostracodinium</i> showed negative correlations. Meanwhile, propionate was positively correlated with <i>Candida</i> and negatively correlated with <i>Bullera</i>. The PICRUSt functional profile prediction indicated that the xenobiotics biodegradation and metabolism, the lipid, amino acid, terpenoids, and polyketides metabolisms of the FTMR group were significantly higher than that of the TMR group. The results imply that FTMR can increase lipid and amino acid metabolism, and modulate the rumen microbiome and improve ruminal fermentation.
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