Insights on Alterations to the Rumen Ecosystem by Nitrate and Nitrocompounds

Abstract

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.

Rumen microbial responses to supplemental nitrate. II. Potential interactions with live yeast culture on the prokaryotic community and methanogenesis in continuous culture

“…The percentage of protozoal N derived from bacterial N is low in the current study, probably because of feed N contamination of protozoal samples; thus, protozoal 15 N enrichment was diluted and could not be fixed (data not shown) by the boiling approach described by Ye et al (2018). Although the potential for denitrification of nitrates to N 2 or N 2 O has also been speculated to become a more prevalent route of NO 2 − reduction while CH 4 emission is suppressed (Liu et al, 2017), Latham et al (2016) summarized denitrification to be minor in the rumen but suggested that such alternative routes deserve future research. The lack (P > 0.15) of treatment effect on bacterial N flow or bacterial N derived from NH 3 -N does not support decreased NH 3 -N assimilation.…”

“…As expected, CH 4 emission was decreased (P = 0.02) by 28.5% by the main effect of adding NO 3 − , but our hypothesis for an interaction with LYC could not be supported (Table 2). Nitrate thermodynamically outcompetes for electrons compared with methanogenesis, and its reduction pathway intermediates (NO 2 − and NO) are known inhibitors of methanogenesis (Latham et al, 2016;Yang et al, 2016). According to a review from Knapp et al (2014), electron acceptors NO 3 − and SO 4 2− decreased emission of CH 4 by an average of 16% in cited reports.…”

Urea plus nitrate pretreatment of rice and wheat straws enhances degradation and reduces methane production inin vitroruminal culture

“…In accordance with expectation, urea+nitrate pretreatment substantially decreased ( P < 0.05) copy numbers of methanogens for both straws in comparison with urea pretreatment and control (Table ). Copy numbers of methanogens may have been lowered partly due to the toxicity of nitrite, the intermediate product as nitrate diverts into ammonium . Another explanation could be that nitrate competes for the hydrogen needed for methanogenesis, because nitrate reduction to ammonium utilizes reducing equivalents more effectively than the reduction of carbon dioxide to methane.…”

“…Copy numbers of methanogens may have been lowered partly due to the toxicity of nitrite, the intermediate product as nitrate diverts into ammonium. 35,42 Another explanation could be that nitrate competes for the hydrogen needed for methanogenesis, DMD, dry matter degradation; NDFD, neutral detergent fiber degradation; GP, total gas production; k GP , fraction rate of total gas production; k methane , fraction rate of methane production; DM, dry matter; DDM, digestible dry matter. Means in the same row with different letters (a, b, c) differ (P < 0.05).…”

Mathematical Model for Predicting the Growth Probability of Staphylococcus aureus in Combinations of NaCl and NaNO2under Aerobic or Evacuated Storage Conditions

“…In processed meats, NaNO 2 plays a role in color fixing and inhibiting pathogenic bacteria, such as Listeria monocytogenes , Clostridium botulinum , and Staphylococcus aureus (Hospital et al , 2016; Karina et al , 2011; Latham et al , 2016; Tompkin et al , 1973). Although NaNO 2 substitutes may fix the color in processed meat products, most have no antimicrobial activity.…”