ABSTRACT The objectives of the trial were to study the effects of dietary crude protein (CP) and tannic acid (TA) on rumen fermentation, microbiota and nutrient digestion in beef cattle. Eight growing beef cattle (live weight 350 ± 25 kg) were allocated in a 2 × 2 crossover design using two levels of dietary CP [111 g/kg dry matter (DM) and 136 g/kg DM] and two levels of TA (0 and 16.9 g/kg DM) as experimental treatments. Each experimental period lasted 19 d, consisting of 14-d adaptation and 5-d sampling. The impacts of dietary CP and TA on ruminal microbiota were analysed using high-throughput sequencing of 16S rRNA gene. Results indicated that no interactions between dietary CP and TA were found on rumen fermentation and nutrient digestibility. Increasing dietary CP level from 111 to 136 g/kg DM increased the ruminal concentrations of ammonia nitrogen (NH3-N) (p < 0.01) and improved the CP digestibility (p < 0.001). Adding TA at 16.9 g/kg DM inhibited rumen fermentation and decreased the digestibility of dietary CP (p < 0.001), DM (p < 0.05) and organic matter (p < 0.01). Increasing the dietary CP level or adding TA did not affect the relative abundances of the major bacteria Firmicutes and Proteobacteria at the phylum level and Prevotella_1 and Christensenellaceae_R-7_group at the genus level, even though adding TA increased the Shannon index of the ruminal bacterial community. TA was partly hydrolysed to pyrogallol, gallic acid and resorcinol in rumen fluid and the inhibitory effects of TA on rumen fermentation and nutrient digestibility could have been resulted from the TA metabolites including pyrogallol, gallic acid and resorcinol as well as the protein-binding effect.

中文翻译：

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日粮粗蛋白和单宁酸对肉牛瘤胃发酵、瘤胃微生物群和营养消化的影响

摘要 本试验的目的是研究日粮粗蛋白 (CP) 和单宁酸 (TA) 对肉牛瘤胃发酵、微生物群和营养消化的影响。八头生长肉牛（活重 350 ± 25 kg）以 2 × 2 交叉设计分配，使用两个水平的日粮 CP [111 g/kg 干物质 (DM) 和 136 g/kg DM] 和两个水平的 TA（ 0 和 16.9 g/kg DM) 作为实验处理。每个实验周期持续 19 d，包括 14 d 适应和 5 d 采样。使用 16S rRNA 基因的高通量测序分析了日粮 CP 和 TA 对瘤胃微生物群的影响。结果表明，日粮 CP 和 TA 之间在瘤胃发酵和养分消化率方面没有相互作用。将日粮 CP 水平从 111 g/kg DM 增加到 136 g/kg DM 增加了瘤胃中氨氮 (NH3-N) 的浓度（p < 0.01）并提高了 CP 的消化率（p < 0.001）。添加 16.9 g/kg DM 的 TA 会抑制瘤胃发酵并降低日粮 CP (p < 0.001)、DM (p < 0.05) 和有机物 (p < 0.01) 的消化率。尽管添加 TA 增加了瘤胃细菌群落的香农指数，但增加日粮 CP 水平或添加 TA 不会影响门水平的主要细菌厚壁菌和变形菌以及属水平的 Prevotella_1 和 Christensenellaceae_R-7_group 的相对丰度。TA 部分水解为连苯三酚，