Insights on alterations to the rumen ecosystem by nitrate and nitrocompounds

Authors: LATHAM, ELIZABETH - Texas A&M University; Anderson, Robin; PINCHAK, WILLIAM - Texas Agrilife Research; Nisbet, David

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2016
Publication Date: 3/4/2016
Publication URL: https://handle.nal.usda.gov/10113/62331
Citation: Latham, E.A., Anderson, R.C., Pinchak, W.E., Nisbet, D.J. 2016. Insights on alterations to the rumen ecosystem by nitrate and nitrocompounds. Frontiers in Microbiology. 7:228. doi: 10.3389/fmicb.2016.00228.

Interpretive Summary: Nitrate and certain short chain nitrocompounds are chemicals that are being investigated as dietary supplements for cattle and sheep to decrease methane production, a digestive inefficiency that results in the loss of 4-12% of the animal’s dietary energy and contributes nearly 20% of the total U.S. emissions of this potent greenhouse gas. Nitrate acts to reduce methane production because its metabolism provides more energy to the microbes in the animal gut than does the production of methane, and thus is the preferred pathway for digestion. The short chain nitrocompounds also act as a competing energy source for the gut bacteria by directly inhibiting the bacterial species responsible for methane production, as well as several important foodborne pathogens such as Salmonella, Campylobacter, and Listeria. Concerns about the toxicity of nitrate’s intermediate product of digestion and nitrite to the animals means that careful management must be done in order to prevent poisoning. Certain nitrocompounds, such as the naturally occurring nitrocompounds, 3-nitro-1-propionate or 3-nitro-1-propanol, also cause poisoning, so again careful management must be done. Typical risk management procedures to avoid poisonings involve gradually adapting the animals to higher concentrations of nitrate and nitrite; this could possibly be used with the nitrocompounds as well. A number of organisms responsible for nitrate metabolism in the rumen have been characterized as a single rumen bacterium, so far identified as contributing appreciably to nitrocompound metabolism. Appropriate doses of the nitrocompounds and nitrate, whether alone or in combination with probiotic bacteria selected for nitrite and nitrocompound detoxification activity, could be formulated to alleviate risks of toxicity. Further studies are needed to more clearly define benefits and risks of these technologies to make them commercially viable for livestock producers. Ultimately, these technologies may yield an effective feed supplement that can reduce economic and environmental costs of ruminal methane production while providing farmers a new tool to enhance the microbiological safety of the meat and milk they produce for the American consumer.

Technical Abstract: Nitrate and certain short chain nitrocompounds 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 ultimately reduced mainly to ammonia, although small quantities of nitrous oxide may also be produced. Short chain nitrocompounds act as direct inhibitors of methanogenic bacteria, although certain ones 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 increase acetate production and, unlike most other methane-inhibiting supplements, decrease or cause no effects on propionate production. The type added can influence rates of nitrate reduction and, consequently, rates of nitrite accumulation and efficacy of methane reduction, with sodium and potassium salts being reduced more rapidly to nitrite than calcium 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, or to ruminants necessitate management, as animal poisoning may occur via methemoglobinemia. Certain nitrocompounds, such as the naturally occurring nitrocompounds, 3-nitro-1-propionate or 3-nitro-1-propanol also cause poisoning, but in this case via inhibition of succinate dehydrogenase. Typical risk management procedures to avoid toxicity involve gradually adapting the animals to higher concentrations of nitrate and nitrite; this could possibly be used with the nitrocompounds as well. A number of organisms responsible for nitrate metabolism in the rumen have been characterized as a single rumen bacterium, so far identified as contributing appreciably to nitrocompound metabolism. Appropriate doses of the nitrocompounds and nitrate, whether alone or in combination with probiotic bacteria selected for nitrite and nitrocompound detoxification activity, could also be formulated to alleviate risks of toxicity. Further studies are needed to more clearly define benefits and risks of these technologies to make them saleable for livestock producers.