[1] WANG Z N,KLIPFELL E,BENNETT B J,et al.Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease[J].Nature,2011,472(7341):57-63.

[2] WANG Z N,ROBERTS A B,BUFFA J A,LEVISON B S,et al.Non-lethal inhibition of gut microbial trimethylamine production for the treatment of atherosclerosis[J].Cell,2015,163(7):1585-1595.

[3] ZHU W,BUFFA J A,WANG Z,et al.Flavin monooxygenase 3,the host hepatic enzyme in the metaorganismal trimethylamine N-oxide-generating pathway,modulates platelet responsiveness and thrombosis risk[J].Journal of Thrombosis and Haemostasis,2018,16(9):1857-1872.

[4] WU G Y.Principles of animal nutrition[M].Boca Raton:CRC Press,2017.
[5] ATKINS K B,ERDMAN R A,VANDERSALL J H.Dietary choline effects on milk yield and duodenal choline flow in dairy cattle[J].Journal of Dairy Science,1988,71(1):109-116.

[6] SHARMA B K,ERDMAN R A.Effects of high amounts of dietary choline supplementation on duodenal choline flow and production responses of dairy cows[J].Journal of Dairy Science,1988,71(10):2670-2676.

[7] JIN W,CHENG Y F,ZHU W Y.The community structure of
Methanomassiliicoccales in the rumen of Chinese goats and its response to a high-grain diet[J].Journal of Animal Science and Biotechnology,2017,8:47.
[8] WEATHERBURN M W.Phenol-hypochlorite reaction for determination of ammonia[J].Analytical Chemistry,1967,39(8):971-974.

[9] XIN H,LANDERAS V,DOBRE M A,et al.Mechanism of prominent trimethylamine oxide (TMAO) accumulation in hemodialysis patients[J].PLoS One,2015,10(12):e0143731.
[10] JEYANATHAN J,KIRS M,RONIMUS R S,et al.Methanogen community structure in the rumens of farmed sheep,cattle and red deer fed different diets[J].FEMS Microbiology Ecology,2011,76(2):311-326.

[11] CAMPO A M D,BODEA S,HAMER H A,et al.Characterization and detection of a widely distributed gene cluster that predicts anaerobic choline utilization by human gut bacteria[J].mBio,2015,6(2):e00042-15.
[12] HJELMSØ M H,HANSEN L H,BÆLUM J,et al.High-resolution melt analysis for rapid comparison of bacterial community compositions[J].Applied and Environmental Microbiology,2014,80(12):3568-3575.

[13] XIE F,ZHANG L L,JIN W,et al.Methane emission,rumen fermentation,and microbial community response to a nitrooxy compound in low-quality forage fed
Hu sheep[J].Current Microbiology,2019,76(4):435-441.

[14] EDGAR R C.UPARSE:highly accurate OTU sequences from microbial amplicon reads[J].Nature Methods,2013,10(10):996-998.

[15] LOZUPONE C,KNIGHT R.UniFrac:a new phylogenetic method for comparing microbial communities[J].Applied and Environmental Microbiology,2005,71(12):8228-8235.

[16] QUAST C,PRUESSE E,YILMAZ P,et al.The SILVA ribosomal RNA gene database project:improved data processing and web-based tools[J].Nucleic Acids Research,2013,41(1):D590-D596.
[17] SEGATA N,IZARD J,WALDRON L,et al.Metagenomic biomarker discovery and explanation[J].Genome Biology,2011,12(6):R60.
[18] NEILL A R,GRIME D W,DAWSON R M.Conversion of choline methyl groups through trimethylamine into methane in the rumen[J].Biochemical Journal,1978,170(3):529-535.

[19] KELLY W J,LEAHY S C,KAMKE J,et al.Occurrence and expression of genes encoding methyl-compound production in rumen bacteria[J].Animal Microbiome,2019,1:15.
[20] CRACIUN S,BALSKUS E P.Microbial conversion of choline to trimethylamine requires a glycyl radical enzyme[J].Proceedings of the National Academy of Sciences of the United States of America,2012,109(52):21307-21312.

[21] DAWSON R M,GRIME D W,LINDSAY D B.On the insensitivity of sheep to the almost complete microbial destruction of dietary choline before alimentary-tract absorption[J].Biochemical Journal,1981,196(2):499-504.

[22] ST-PIERRE B,CERSOSIMO L M,ISHAQ S L,et al.Toward the identification of methanogenic archaeal groups as targets of methane mitigation in livestock animals[J].Frontiers in Microbiology,2015,6:776.