Our aim was to simultaneously investigate the gut bacteria typical characteristic and conduct rumen metabolites profiling of high production dairy cows when compared to low‐production dairy cows. The bacterial differences in rumen fluid and feces were identified by 16S rDNA gene sequencing. The metabolite differences were identified by metabolomics profiling with liquid chromatography mass spectrometry ( LC ‐ MS ). The results indicated that the high‐production dairy cows presented a lower rumen bacterial richness and species evenness when compared to low‐production dairy cows. At the phylum level, the high‐production cows increased the abundance of Proteobacteria and decreased the abundance of Bacteroidetes, SR 1, Verrucomicrobia, Euryarchaeota, Planctomycetes, Synergistetes, and Chloroflexi significantly ( p < 0.05). At the genus level, the rumen fluid of the high‐production group was significantly enriched for Butyrivibrio , Lachnospira , and Dialister ( p < 0.05). Meanwhile, rumen fluid of high‐production group was depleted for Prevotella, Succiniclasticum, Ruminococcu, Coprococcus, YRC 22, CF 231, 02d06, Anaeroplasma, Selenomonas , and Ruminobacter significantly ( p < 0.05). A total of 92 discriminant metabolites were identified between high‐production cows and low‐production cows. Compared to rumen fluid of low‐production dairy cows, 10 differential metabolites were found up‐regulated in rumen fluid of high‐production dairy cows, including 6alpha‐Fluoropregn‐4‐ene‐3,20‐dione, 3‐Octaprenyl‐4‐hydroxybenzoate, disopyramide, compound III (S), 1,2‐Dimyristyl‐sn‐glycerol, 7,10,13,16‐Docosatetraenoic acid, ferrous lactate, 6‐Deoxyerythronolide B, vitamin D2, L‐Olivosyl‐oleandolide. The remaining differential metabolites were found down‐regulated obviously in high‐production cows. Metabolic pathway analyses indicated that most increased abundances of rumen fluid metabolites of high‐yield cows were related to metabolic pathways involving biosynthesis of unsaturated fatty acids, steroid biosynthesis, ubiquinone and other terpenoid‐quinone biosynthesis. Most down‐regulated metabolic pathways were relevant to nucleotide metabolism, energy metabolism, lipid metabolism and biosynthesis of some antibiotics.

An animal feeding trial was conducted on 18 seven‐day‐old Holstein dairy bull calves weighing 42 ± 3 kg each. Calves were randomly assigned into three groups ( n = 6 each). The dietary treatments were as follows: (1) milk and starter for the control group ( MS ), (2) supplementation of oat hay from week 2 on the basis of milk and starter ( MSO 2), and (3) supplementation of oat hay from week 6 on the basis of milk and starter ( MSO 6). All animals were fed starter and oat hay ad libitum. The major phyla in the different groups of rumen fluid included Firmicutes, Actinobacteria, Bacteroidetes, Proteobacteria, and Euryarchaeota. The major genera were identified, and major genera proportions in the three groups were as follows: Methanobrevibacter (Euryarchaeota), 2.1%, 1.7%, and 2.1%; Olsenella (Actinobacteria), 23.9%, 17.7%, and 12.8%; Prevotella (Bacteroidetes), 10.5%, 16.5%, and 19.2%; Dialister (Firmicutes), 3.3%, 4.1%, and 2.8%; Succiniclasticum (Firmicutes), 3.8%, 4.7%, and 9.2%; and Sharpea (Firmicutes), 0.4%, 2.5%, and 0.2%, respectively. There were no significant differences in the various phyla among the three groups ( p > .05). The results showed that calves hay supplementation time did not affect the diversity of the rumen microbiota in the suckling calves. However, the hay supplementation altered the proportion of the various microbial populations, supplementation of oat hay from week 2 on the basis of milk and starter could improve calves rumen pH .

Holstein dairy cows, Chinese Luxi Yellow cattle, Chinese Laoshan dairy goats, and Chinese Bohai Black cattle were selected for the study. The 16S rDNA sequencing technique was used to analyze the microflora in the digestive tract. The rumen flora in high milk‐yield Holstein dairy cows showed significantly higher proportions of Treponema, Butyrivibrio , Coprococcus , Shuttleworthia , Lachnospira, and Selenomon as, compared with the rumen flora in Chinese Bohai Black cattle and Chinese Luxi Yellow cattle ( p < 0.05). In addition, the abundances of Succiniclasticum, Ruminococcus, and Fibrobacter in the rumen fluid of high‐yield dairy cows were significantly higher than those in rumen flora of dairy goats. Compared with ruminal flora in Chinese Luxi Yellow cattle, the rumen flora in high‐yield dairy cattle showed significantly higher Prevotella . Compared with the rumen flora in Chinese Laoshan dairy goats, Chinese Bohai Black cattle, and Chinese Luxi Yellow cattle, the flora in high‐yielding dairy cows showed significantly lower proportions of CF231, 02d06, Oscillospira , RFN20, Desulfovibrio , Methanobrevibacter, and SHD‐231. In addition, compared with the rumen flora in dairy goats, the rumen flora in high‐yielding dairy cattle displayed significantly lower proportion of Enterococcus . Compared with the rumen flora in Chinese Bohai Black cattle, the flora in high‐yielding dairy cattle exhibited significantly lower Ruminococcus , YRC22, Pseudobutyrivibrio , L7A_E11, BF311, p‐75‐a5, and Dehalobacterium . Compared with the rumen flora in Chinese Luxi Yellow cattle, the flora in the high‐yield dairy cows also displayed significantly lower proportions of Ruminococcus , YRC22, BF311, Paludibacter, and Dehalobacterium .