Trimethylamine oxide (TMAO) is a microbiota-derived metabolite, and numerous studies have shown that it could regulate fat metabolism in humans and mice. However, few studies have focused on the effects of TMAO on fat deposition in growing-finishing pigs. This study aimed to investigate the effect of TMAO on fat deposition and intestinal microbiota in growing-finishing pigs. Sixteen growing pigs were randomly divided into 2 groups and fed with a basal diet with 0 or 1 g/kg TMAO for 149 d. The intestinal microbial profiles, fat deposition indexes, and fatty acid profiles were measured. These results showed that TMAO supplementation had a tendency to decrease lean body mass (P < 0.1) and significantly increased backfat thickness (P < 0.05), but it did not affect growth performance. TMAO significantly increased total protein (TP) concentration, and reduced alkaline phosphatase (ALP) concentration in serum (P < 0.05). TMAO increased the α diversity of the ileal microbiota community (P < 0.05), and it did not affect the colonic microbial community. TMAO supplementation significantly increased acetate content in the ileum, and Proteobacteria and Escherichia-shigella were significantly enriched in the TMAO group (P < 0.05). In addition, TMAO decreased fat content, as well as the ratio of linoleic acid, n-6 polyunsaturated fatty acids (PUFA), and PUFA in the liver (P < 0.05). On the contrary, TMAO increased intramuscular fat content of the longissimus dorsi muscle, whereas the C18:2n6c ratio was increased, and the n-6 PUFA:PUFA ratio was decreased (P < 0.05). In vitro, 1 mM TMAO treatment significantly upregulated the expression of FASN and SREBP1 in C2C12 cells (P < 0.05). Nevertheless, TMAO also increased adipocyte area and decreased the CPT-1B expression in subcutaneous fat (P < 0.05). Taken together, TMAO supplementation regulated ileal microbial composition and acetate production, and regulated fat distribution and fatty acid composition in growing-finishing pigs. These results provide new insights for understanding the role of TMAO in humans and animals.

三甲胺氧化物（TMAO）是一种源自微生物群的代谢物，大量研究表明它可以调节人类和小鼠的脂肪代谢。然而，很少有研究关注TMAO对生长肥育猪脂肪沉积的影响。本研究旨在探讨TMAO对生长肥育猪脂肪沉积和肠道微生物群的影响。将16头生长猪随机分为2组，饲喂添加0或1 g/kg TMAO的基础日粮，饲喂149 d。测量肠道微生物谱、脂肪沉积指数和脂肪酸谱。结果表明，补充TMAO有降低去脂体重（P <0.1）和显着增加背膘厚度（P <0.05）的趋势，但不影响生长性能。TMAO显着升高血清总蛋白（TP）浓度，降低血清碱性磷酸酶（ALP）浓度（P < 0.05）。TMAO增加了回肠微生物群落的α多样性（P < 0.05），并且不影响结肠微生物群落。补充TMAO显着增加回肠中乙酸含量， TMAO组变形菌和大肠杆菌明显富集（P < 0.05）。此外，TMAO还降低了脂肪含量，以及肝脏中亚油酸、n-6多不饱和脂肪酸（PUFA）和PUFA的比例（P < 0.05）。相反，TMAO 增加背最长肌肌内脂肪含量，而 C18:2n6c 比值增加，n-6 PUFA:PUFA 比值下降（P < 0.05）。体外，1 mM TMAO 处理显着上调C2C12 细胞中FASN和SREBP1的表达（ P < 0.05）。然而，TMAO也增加了脂肪细胞面积并降低了皮下脂肪中CPT-1B的表达（P < 0.05）。总而言之，TMAO 补充剂可调节生长育肥猪的回肠微生物组成和乙酸盐产生，并调节脂肪分布和脂肪酸组成。这些结果为理解TMAO在人类和动物中的作用提供了新的见解。