Latham Elizabeth A, Anderson Robin C, Pinchak William E, Nisbet David J
Department of Animal Science, Texas A&M UniversityCollege Station, TX, USA; Texas A&M AgriLife ResearchVernon, TX, USA.
Food and Feed Safety Research Unit, Southern Plains Agricultural Research Center, United States Department of Agriculture, Agricultural Research Service College Station, TX, USA.
Front Microbiol. 2016 Mar 4;7:228. doi: 10.3389/fmicb.2016.00228. eCollection 2016.
Nitrate and certain short chain nitrocompounds and nitro-oxy compounds are being investigated as dietary supplements to reduce economic and environmental costs associated with ruminal methane emissions. Thermodynamically, nitrate is a preferred electron acceptor in the rumen that consumes electrons at the expense of methanogenesis during dissimilatory reduction to an intermediate, nitrite, which is primarily reduced to ammonia although small quantities of nitrous oxide may also be produced. Short chain nitrocompounds act as direct inhibitors of methanogenic bacteria although certain of these compounds may also consume electrons at the expense of methanogenesis and are effective inhibitors of important foodborne pathogens. Microbial and nutritional consequences of incorporating nitrate into ruminant diets typically results in increased acetate production. Unlike most other methane-inhibiting supplements, nitrate decreases or has no effect on propionate production. The type of nitrate salt added influences rates of nitrate reduction, rates of nitrite accumulation and efficacy of methane reduction, with sodium and potassium salts being more potent than calcium nitrate salts. Digestive consequences of adding nitrocompounds to ruminant diets are more variable and may in some cases increase propionate production. Concerns about the toxicity of nitrate's intermediate product, nitrite, to ruminants necessitate management, as animal poisoning may occur via methemoglobinemia. Certain of the naturally occurring nitrocompounds, such as 3-nitro-1-propionate or 3-nitro-1-propanol also cause poisoning but via inhibition of succinate dehydrogenase. Typical risk management procedures to avoid nitrite toxicity involve gradually adapting the animals to higher concentrations of nitrate and nitrite, which could possibly be used with the nitrocompounds as well. A number of organisms responsible for nitrate metabolism in the rumen have been characterized. To date a single rumen bacterium is identified as contributing appreciably to nitrocompound metabolism. Appropriate doses of the nitrocompounds and nitrate, singly or in combination with probiotic bacteria selected for nitrite and nitrocompound detoxification activity promise to alleviate risks of toxicity. Further studies are needed to more clearly define benefits and risk of these technologies to make them saleable for livestock producers.
硝酸盐以及某些短链硝基化合物和硝基氧化合物正在作为膳食补充剂进行研究，以降低与瘤胃甲烷排放相关的经济和环境成本。从热力学角度来看，硝酸盐是瘤胃中一种首选的电子受体，在异化还原为中间产物亚硝酸盐的过程中，它会消耗电子，从而以甲烷生成减少为代价，亚硝酸盐主要被还原为氨，不过也可能会产生少量一氧化二氮。短链硝基化合物是产甲烷细菌的直接抑制剂，尽管其中某些化合物也可能以甲烷生成减少为代价消耗电子，并且是重要食源性病原体的有效抑制剂。将硝酸盐纳入反刍动物日粮的微生物和营养后果通常会导致乙酸盐产量增加。与大多数其他抑制甲烷的补充剂不同，硝酸盐会降低丙酸盐产量或对其产量没有影响。添加的硝酸盐盐类类型会影响硝酸盐还原速率、亚硝酸盐积累速率和甲烷减少效果，钠盐和钾盐比硝酸钙盐更有效。向反刍动物日粮中添加硝基化合物的消化后果更具变数，在某些情况下可能会增加丙酸盐产量。由于瘤胃中硝酸盐的中间产物亚硝酸盐对反刍动物具有毒性，因此需要进行管理，因为动物可能会因高铁血红蛋白血症而中毒。某些天然存在的硝基化合物，如3-硝基丙酸或3-硝基丙醇也会导致中毒，但却是通过抑制琥珀酸脱氢酶。避免亚硝酸盐毒性的典型风险管理程序包括让动物逐渐适应更高浓度的硝酸盐和亚硝酸盐，这也可能适用于硝基化合物。已经对瘤胃中负责硝酸盐代谢的多种微生物进行了表征。迄今为止，已鉴定出一种瘤胃细菌对硝基化合物代谢有显著贡献。适当剂量的硝基化合物和硝酸盐，单独使用或与具有亚硝酸盐和硝基化合物解毒活性的益生菌联合使用，有望降低毒性风险。需要进一步研究以更明确地界定这些技术的益处和风险，使其能够面向牲畜生产者进行销售。
