It is known that nitrate inhibits ruminal methanogenesis, mainly through competition with hydrogenotrophic methanogens for available hydrogen (H₂) and also through toxic effects on the methanogens. However, there is limited knowledge about its effects on the others members of ruminal microbiota and their metabolites. In this study, we investigated the effects of dietary nitrate inclusion on enteric methane (CH₄) emission, temporal changes in ruminal microbiota, and fermentation in Holstein calves. Eighteen animals were maintained in individual pens for 45 d. Animals were randomly allocated to either a control (CTR) or nitrate (NIT, containing 15 g of calcium nitrate/kg dry matter) diets. Methane emissions were estimated using the sulfur hexafluoride (SF₆) tracer method. Ruminal microbiota changes and ruminal fermentation were evaluated at 0, 4, and 8 h post-feeding. In this study, feed dry matter intake (DMI) did not differ between dietary treatments (P > 0.05). Diets containing NIT reduced CH₄ emissions by 27% (g/d) and yield by 21% (g/kg DMI) compared to the CTR (P < 0.05). The pH values and total volatile fatty acids (VFA) concentration did not differ between dietary treatments (P > 0.05) but differed with time, and post-feeding (P < 0.05). Increases in the concentrations of ruminal ammonia nitrogen (NH₃–N) and acetate were observed, whereas propionate decreased at 4 h post-feeding with the NIT diet (P < 0.05). Feeding the NIT diet reduced the populations of total bacteria, total methanogens, Ruminococcus albus and Ruminococcus flavefaciens, and the abundance of Succiniclasticum, Coprococcus, Treponema, Shuttlewortia, Succinivibrio, Sharpea, Pseudobutyrivibrio, and Selenomona (P < 0.05); whereas, the population of total fungi, protozoa, Fibrobacter succinogenes, Atopobium and Erysipelotrichaceae L7A_E11 increased (P < 0.05). In conclusion, feeding nitrate reduces enteric CH₄ emissions and the methanogens population, whereas it decreases the propionate concentration and the abundance of bacteria involved in the succinate and acrylate pathways. Despite the altered fermentation profile and ruminal microbiota, DMI was not influenced by dietary nitrate. These findings suggest that nitrate has a predominantly direct effect on the reduction of methanogenesis and propionate synthesis.

众所周知，硝酸盐主要通过与氢营养型产甲烷菌竞争可用氢 (H ₂ ) 以及对产甲烷菌的毒性作用来抑制瘤胃产甲烷。然而，关于其对瘤胃微生物群其他成员及其代谢物的影响的知识有限。在本研究中，我们研究了日粮硝酸盐含量对肠道甲烷 (CH ₄ ) 排放、瘤胃微生物群的时间变化和荷斯坦犊牛发酵的影响。18 只动物在单独的围栏中饲养 45 天。动物被随机分配到对照 (CTR) 或硝酸盐 (NIT，含有 15 g 硝酸钙/kg 干物质) 饮食。使用六氟化硫 (SF ₆) 示踪法。在饲喂后 0、4 和 8 小时评估瘤胃微生物群的变化和瘤胃发酵。在这项研究中，饲料干物质摄入量（DMI）在日粮处理之间没有差异（P  > 0.05）。与 CTR 相比，含有 NIT 的饮食减少了 27% (g/d) 的CH ₄排放和 21% (g/kg DMI) 的产量 ( P  < 0.05)。pH 值和总挥发性脂肪酸 (VFA) 浓度在日粮处理之间没有差异 ( P  > 0.05)，但随时间和喂养后的差异 ( P  < 0.05)。观察到瘤胃氨氮 (NH ₃ -N) 和醋酸盐浓度增加，而丙酸盐在饲喂 NIT 饲料后 4 小时下降（P < 0.05)。喂养NIT饮食降低的总细菌，总产甲烷菌，的种群瘤胃球菌球菌和瘤胃球菌球菌，和的丰度Succiniclasticum，Coprococcus，密螺旋体属，Shuttlewortia，Succinivibrio，Sharpea，Pseudobutyrivibrio，和Selenomona（P  <0.05）; 而总真菌、原生动物、纤维杆菌 succinogenes、Atopobium和丹毒L7A_E11 的数量增加（P < 0.05)。总之，饲喂硝酸盐可减少肠道 CH ₄排放和产甲烷菌数量，同时降低丙酸盐浓度和参与琥珀酸盐和丙烯酸盐途径的细菌数量。尽管发酵曲线和瘤胃微生物群发生了改变，但 DMI 不受膳食硝酸盐的影响。这些发现表明硝酸盐对减少产甲烷和丙酸盐合成具有主要的直接影响。