Within the rumen, nitrate can serve as an alternative sink for aqueous hydrogen [H₂(aq)] accumulating during fermentation, producing nitrite, which ideally is further reduced to ammonium but can accumulate under conditions not yet explained. Defaunation has also been associated with decreased methanogenesis in meta-analyses because protozoa contribute significantly to H₂ production. In the present study, we applied a 2 × 2 factorial treatment arrangement in a 4 × 4 Latin square design to dual-flow continuous culture fermentors (n = 4). Treatments were control without nitrate (−NO₃⁻) versus with nitrate (+NO₃⁻; 1.5% of diet dry matter), factorialized with normal protozoa (faunated, FAUN) versus defaunation (DEF) by decreasing the temperature moderately and changing filters over the first 4 d of incubation. We detected no main effects of DEF or interaction of faunation status with +NO₃⁻. The main effect of +NO₃⁻ increased H₂(aq) by 11.0 µM (+117%) compared with −NO₃⁻. The main effect of +NO₃⁻ also decreased daily CH₄ production by 8.17 mmol CH₄/d (31%) compared with −NO₃⁻. Because there were no treatment effects on neutral detergent fiber digestibility, the main effect of +NO₃⁻ also decreased CH₄ production by 1.43 mmol of CH₄/g of neutral detergent fiber degraded compared with −NO₃⁻. There were no effects of treatment on other nutrient digestibilities, N flow, or microbial N flow per gram of nutrient digested. The spike in H₂(aq) after feeding NO₃⁻ provides evidence that methanogenesis is inhibited by substrate access rather than concentration, regardless of defaunation, or by direct inhibition of NO₂⁻. Methanogens were not decreased by defaunation, suggesting a compensatory increase in non-protozoa-associated methanogens or an insignificant contribution of protozoa-associated methanogens. Despite adaptive reduction of NO₃⁻ to NH₄⁺ and methane inhibition in continuous culture, practical considerations such as potential to depress dry matter intake and on-farm ration variability should be addressed before considering NO₃⁻ as an avenue for greater sustainability of greenhouse gas emissions in US dairy production.

在瘤胃中，硝酸盐可作为发酵过程中积累的氢水[H ₂（aq）]的替代汇，产生亚硝酸盐，理想情况下将其进一步还原为铵，但可以在尚未说明的条件下积累。由于原生动物显着促进了H _2的产生，因此在荟萃分析中，脱落也与甲烷生成减少有关。在本研究中，我们将4×4拉丁方形设计中的2×2阶乘处理布置应用于双流连续培养发酵罐（n = 4）。处理为控制，而不硝酸盐（-NO ₃ ^- ）相对于用硝酸（+ NO ₃ ^-; 1.5％的日粮干物质），通过温和降低温度并在孵育的前4 d更换过滤器，可以用正常原生动物（动植物因子，FAUN）分解因子（DEF）分解因子。我们检测到DEF或faunation地位的互动与+ NO无主效应₃ ^- 。+ NO的主要作用₃ ^-增加ħ ₂ 11.0（水溶液）μ中号与-NO相比（+ 117％）₃ ^- 。+ NO的主要作用₃ ^-也降低每日CH ₄ 8.17毫摩尔CH生产₄与-NO相比/ d（31％）₃ ^-。因为有在中性洗涤剂纤维消化率无治疗效果，+ NO的主要作用₃ ^-也降低CH ₄的生产由1.43毫摩尔的CH ₄ /中性洗涤剂纤维的克降解与-NO相比₃ ^- 。处理对每克消化的养分的其他养分消化率，氮流量或微生物氮流量没有影响。在H中的尖峰₂ NO喂食后（水溶液）₃ ^-提供的证据表明甲烷是通过基底入口而不是浓度的抑制，无论defaunation的，或通过直接抑制NO的₂ ^-。毁灭并没有减少产甲烷菌，这表明非原生动物相关产甲烷菌的代偿性增加或原生动物相关产甲烷菌的微不足道的贡献。尽管自适应还原NO ₃ ^-以NH ₄ ⁺和甲烷抑制在连续培养，实际考虑因素，如潜在压下干物质采食量和农场配给变异应当考虑NO前处理₃ ^-温室的更大的可持续性的途径美国乳制品生产中的天然气排放。