Serum trimethylamine-N-oxide and gut microbiome alterations are associated with cholesterol deposition in the liver of laying hens fed with rapeseed meal

Sinapine derived from cruciferous plants could be converted into trimethylamine by intestinal microbiota. Its metabolite, trimethylamine N-oxide (TMAO), is closely linked to increased risk of cardiovascular disease and fat deposition in mammals. Hens fed with rapeseed meal (RSM) suffered from fatty liver hemorrhage syndrome (FLHS). This study was conducted to investigate whether RSM-induced fatty liver is due to TMAO via altering microbiota composition and diversity. At 33 weeks of age, 600 laying hens were randomly divided into 5 treatment groups, namely control and 14% RSM treatment groups (DY5, with 16.2% erucic acid [EA] and 74.66% glucosinolate [Gl] contents; MB1, with 3.50% EA and 43.23% Gl contents; DY6, with 6.7% EA and 22.67% Gl contents; XH3, with 44.60% EA and 132.83% Gl contents) for 8 weeks. Results revealed that 3 hens died due to liver hemorrhage after ingesting 14% RSM diet. The 14% RSM decreased serum low-density lipoprotein cholesterol (LDL-C) content (P < 0.01) while tended to increase serum TMAO content compared to the control group (P = 0.08). The 14% RSM diet increased red oil O optical density (P < 0.01), and increased total cholesterol (TC) and LDL-C content in the liver (P < 0.01, and P < 0.01, respectively). The 14% RSM decreased liver total bile acid (TBA) content compared to the control (P < 0.01). The DY6 had a higher TBA content in the liver than the XH3 (P < 0.01). The 14% RSM decreased mRNA abundance of liver X receptors alpha (LXR-α, P = 0.01), and increased mRNA abundance of sterol response element binding protein 2 (SREBP-2, P = 0.04). Results revealed that the in-feed RSM could alter richness and diversity of cecal microbiota compared to the control (P < 0.05). Liver TC content and serum TMAO showed a negative relationship with Proteobacteria and Actinobacteria (P = 0.04). In conclusion, 14% RSM increased liver TC and induced high liver score of FLHS, which was possibly associated with the altered cecal microbiota composition, increased serum TMAO levels and LXR-α and SREBP-2 expressions.