Zoonotic bacterial populations, gut fermentation characteristics and methane production in feedlot steers during oral nitroethane treatment and after the feeding of an experimental chlorate product

Methane mitigation in ruminants with structural analogues and other chemical compounds targeting archaeal methanogenesis pathways

Ruminants are responsible for enteric methane production contributing significantly to the anthropogenic greenhouse gases in the atmosphere. Moreover, dietary energy is lost as methane gas without being available for animal use. Therefore, many mitigation strategies aiming at interventions at animals, diet, and microbiota have been explored by researchers. Specific chemical analogues targeting the enzymes of the methanogenic pathway appear to be more effective in specifically inhibiting the growth of methane-producing archaea without hampering another microbiome, particularly, cellulolytic microbiota. The targets of methanogenesis reactions that have been mainly investigated in ruminal fluid include methyl coenzyme M reductase (halogenated sulfonate and nitrooxy compounds), corrinoid enzymes (halogenated aliphatic compounds), formate dehydrogenase (nitro compounds, e.g., nitroethane and 2-nitroethanol), and deazaflavin (F420) (pterin and statin compounds). Many other potential metabolic reaction targets in methanogenic archaea have not been evaluated properly. The analogues are specifically effective inhibitors of methanogens, but their efficacy to lower methanogenesis over time reduces due to the metabolism of the compounds by other microbiota or the development of resistance mechanisms by methanogens. In this short review, methanogen populations inhabited in the rumen, methanogenesis pathways and methane analogues, and other chemical compounds specifically targeting the metabolic reactions in the pathways and methane production in ruminants have been discussed. Although many methane inhibitors have been evaluated in lowering methane emission in ruminants, advancement in unravelling the molecular mechanisms of specific methane inhibitors targeting the metabolic pathways in methanogens is very limited.

Inhibitory Effect of Select Nitrocompounds and Chlorate against Yersinia ruckeri and Yersinia aleksiciae In Vitro

Yersinia ruckeri is an important fish pathogen causing enteric redmouth disease. Antibiotics have traditionally been used to control this pathogen, but concerns of antibiotic resistance have created a need for alternative interventions. Presently, chlorate and certain nitrocompounds were tested against Y. ruckeri as well as a related species within the genus, Y. aleksiciae, to assess the effects of these inhibitors. The results reveal that 9 mM chlorate had no inhibitory effect against Y. ruckeri, but inhibited growth rates and maximum optical densities of Y. aleksciciae by 20–25% from those of untreated controls (0.46 h−1 and 0.29 maximum optical density, respectively). The results further reveal that 2-nitropropanol and 2-nitroethanol (9 mM) eliminated the growth of both Y. ruckeri and Y. aleksiciae during anaerobic or aerobic culture. Nitroethane, ethyl nitroacetate and ethyl-2-nitropropionate (9 mM) were less inhibitory when tested similarly. Results from a mixed culture of Y. ruckeri with fish tank microbes and of Y. aleksiciae with porcine fecal microbes reveal that the anti-Yersinia activity of the tested nitrocompounds was bactericidal, with 2-nitropropanol and 2-nitroethanol being more potent than the other tested nitrocompounds. The anti-Yersinia activity observed with these tested compounds warrants further study to elucidate the mechanisms of action and strategies for their practical application.

Dynamics of Gastrointestinal Activity and Ruminal Absorption of the Methane-Inhibitor, Nitroethane, in Cattle

Nitroethane is a potent methane-inhibitor for ruminants but little is known regarding simultaneous effects of repeated administration on pre- and post-gastric methane-producing activity and potential absorption and systemic accumulation of nitroethane in ruminants. Intraruminal administration of 120 mg nitroethane/kg body weight per day to Holstein cows (n = 2) over a 4-day period transiently reduced (P < 0.05) methane-producing activity of rumen fluid as much as 3.6-fold while concomitantly increasing (P < 0.05) methane-producing activity of feces by as much as 8.8-fold when compared to pre-treatment measurements. These observations suggest a bacteriostatic effect of nitroethane on ruminal methanogen populations resulting in increased passage of viable methanogens to the lower bovine gut. Ruminal VFA concentrations were also transiently affected by nitroethane administration (P < 0.05) reflecting adaptive changes in the rumen microbial populations. Mean (± SD) nitroethane concentrations in plasma of feedlot steers (n = 6/treatment) administered 80 or 160 mg nitroethane/kg body weight per day over a 7-day period were 0.12 ± 0.1 and 0.41 ± 0.1 μmol/mL 8 h after the initial administration indicating rapid absorption of nitroethane, with concentrations peaking 1 day after initiation of the 80 or 160 mg nitroethane/kg body weight per day treatments (0.38 ± 0.1 and 1.14 ± 0.1 μmol/mL, respectively). Plasma nitroethane concentrations declined thereafter to 0.25 ± 0.1 and 0.78 ± 0.3 and to 0.18 ± 0.1 and 0.44 ± 0.3 μmol/mL on days 2 and 7 for the 80 or 160 mg nitroethane/kg body weight per day treatment groups, respectively, indicating decreased absorption due to increased ruminal nitroethane degradation or to more rapid excretion of the compound.

Astragallus mollissimus plant extract: a strategy to reduce ruminal methanogenesis

Ruminal methanogenesis is considered an inefficient process as it can result in the loss of 4 to 12% of the total energy consumed by the ruminant. Recent studies have shown that compounds such as nitroethane, 2-nitroethanol, 2-nitro-1-propanol, and 3-nitro-1-propionic acid are capable of inhibiting methane production during in vitro studies. However, all of these nitrocompounds came from a synthetic origin, which could limit their use. In contrast, some plants of the Astragallus genus produce a natural nitrocompound, although its anti-methanogenic effect has not been evaluated. To determine the anti-methanogenic effect, in vitro cultures of freshly collected mixed populations of ruminal microbes were supplemented with A. mollissimus extracts (MISER). Cultures supplemented with 2-nitroethanol, ethyl 2-nitroacetate, or nitroethane were used as positive controls whereas distilled water was added to the untreated control tubes. After a 24 h incubation period, the methane production was reduced by more than 98% for the samples treated with A. mollissimus extract (P < 0.05) compared to the untreated controls (10.2 ± 0.1 mmol mL^-1 incubated liquid). Cultures supplemented with MISER produced a greater (P < 0.05) amount of total VFA, compared to the rest of treated and untreated cultures. Considering that there are significant differences between MISER treatment, positive controls and untreated cultures (P < 0.05) regarding the amounts of total gas, gas composition (CH₄ and H₂), and the amount of VFA produced, it is concluded that Astragallus mollissimus poses an alternative strategy to reduce ruminal methanogenesis. To further explore such alternative, it is necessary to determine if the metabolization byproducts are safe and/or useful for the animal.

Roles of Nitrocompounds in Inhibition of Foodborne Bacteria, Parasites, and Methane Production in Economic Animals

Simple Summary

Supplementation of nitrocompounds in animal diets has been studied to investigate their effects on economic animals. It has been known that nitrocompounds are capable of inhibiting pathogens, parasites, methane and ammonia production. The toxicity, metabolism, and mechanisms of actions have been discussed in the review to conclude the advantages and disadvantages of application of nitrocompounds in animal production.

Abstract

Nitrocompounds are derivatives of hydrocarbons, alcohols, fatty acids, and esters, consisting one or more nitro functional groups. Either natural sources of nitrocompounds or synthetic chemicals have been applied in animal diets to investigate their effects on economic animals, since conjugates of 3-nitropropanol and 3-nitropropionic acid were isolated from Astragalus oblongifolius. In this review, emphasis will be placed on nitrocompounds’ antimicrobial activity, toxicity, metabolisms and mechanisms of actions. Nitrocompounds can be metabolized by ruminal microbials, such as Denitrobacterium detoxificans, or alcohol dehydrogenase in the liver. Moreover, it has been found that nitrocompounds are capable of inhibiting pathogens, parasites, methane and ammonia production; however, overdose of nitrocompounds could cause methemoglobinemia or interfere with energy production in mitochondria by inhibiting succinate dehydrogenase.

Nitro-treatment of composted poultry litter; effects on Salmonella, E. coli and nitrogen metabolism

Poultry litter is a potentially valuable crude protein feedstuff for ruminants but must be treated to kill pathogens before being fed. Composting kills pathogens but risks losses of nitrogen due to volatilization or leaching as ammonia. Treatment of poultry litter with ethyl nitroacetate, 3-nitro-1-propionate, ethyl 2-nitropropionate (at 27 µmol/g), decreased numbers of experimentally-inoculated Salmonella Typhimurium (>1.0 log₁₀ compared to controls, 4.2 ± 0.2 log₁₀ CFU/g) but not endogenous Escherichia coli early during simulated composting. By day 9 of simulated composting, Salmonella and E. coli were decreased to non-detectable levels regardless of treatment. Some nitro-treatments preserved uric acid and prevented ammonia accumulation, with 18% more uric acid remaining and 17-24% less ammonia accumulating in some nitro-treated litter than in untreated litter (18.1 ± 3.8 µmol/g and 3.4 ± 1.4 µmol/g, respectively). Results indicate that nitro-treatment may help preserve uric acid in composted litter while aiding Salmonella control.

Rumen Methanogenesis, Rumen Fermentation, and Microbial Community Response to Nitroethane, 2-Nitroethanol, and 2-Nitro-1-Propanol: An In Vitro Study

Nitroethane (NE), 2-nitroethanol (NEOH), and 2-nitro-1-propanol (NPOH) were comparatively examined to determine their inhibitory actions on rumen fermentation and methanogenesis in vitro. Fermentation characteristics, CH₄ and total gas production, and coenzyme contents were determined at 6, 12, 24, 48, and 72 h incubation time, and the populations of ruminal microbiota were analyzed by real-time PCR at 72 h incubation time. The addition of NE, NEOH, and NPOH slowed down in vitro rumen fermentation and reduced the proportion of molar CH₄ by 96.7%, 96.7%, and 41.7%, respectively (p < 0.01). The content of coenzymes F₄₂₀ and F₄₃₀ and the relative expression of the mcrA gene declined with the supplementation of NE, NEOH, and NPOH in comparison with the control (p < 0.01). The addition of NE, NEOH, and NPOH decreased total volatile fatty acids (VFAs) and acetate (p < 0.05), but had no effect on propionate concentration (p > 0.05). Real-time PCR results showed that the relative abundance of total methanogens, Methanobacteriales, Methanococcales, and Fibrobacter succinogenes were reduced by NE, NEOH, and NPOH (p < 0.05). In addition, the nitro-degradation rates in culture fluids were ranked as NEOH (-0.088) > NE (-0.069) > NPOH (-0.054). In brief, the results firstly provided evidence that NE, NEOH, and NPOH were able to decrease methanogen abundance and dramatically decrease mcrA gene expression and coenzyme F₄₂₀ and F₄₃₀ contents with different magnitudes to reduce ruminal CH₄ production.

Nitroethanol in Comparison with Monensin Exhibits Greater Feed Efficiency Through Inhibiting Rumen Methanogenesis More Efficiently and Persistently in Feedlotting Lambs

This study was conducted to determine the dietary supplemental effects of nitroethanol (NEOH) in comparison with monensin on growth performance and estimated methane (CH4) production in feedlotting lambs. Sixty male, small-tailed Chinese Han lambs were arranged at random into three dietary treatment groups: (1) a basal control diet (CTR), (2) the basal diet added with 40 mg/kg monensin (MON), (3) the basal diet added with 277 mg/kg nitroethanol (NEOH). During the 32-day lamb feeding, monensin and nitroethanol were added in period 1 (day 0-16) and then withdrawn in the subsequent period 2 (day 17-32) to determine their withdrawal effects. The average daily gain (ADG) and feed conversion rate in the whole period ranked: NEOH > MON > CTR (p < 0.01), suggesting that the dietary addition of NEOH in comparison with monensin presented a more lasting beneficial effect on feed efficiency. Methane emission was estimated with rumen VFA production and gross energy intake. Both monensin and NEOH addition in comparison with the control remarkably decreased CH4 emission estimate (24.0% vs. 26.4% decrease; p < 0.01) as well as CH4 emission per kg ADG (8.7% vs. 14.0% decrease; p < 0.01), but the NEOH group presented obvious lasting methanogenesis inhibition when they were withdrawn in period 2. Moreover, the in vitro methanogenic activity of rumen fluids was also decreased with monensin or NEOH addition (12.7% vs. 30.5% decrease; p < 0.01). In summary, the dietary addition of NEOH in comparison with monensin presented a greater promoting effect on growth performance in feedlotting lambs by inhibiting rumen methanogenesis more efficiently and persistently.

Paenibacillus 79R4, a potential rumen probiotic to enhance nitrite detoxification and methane mitigation in nitrate-treated ruminants

The effects of supplemental nitrate administered alone or with a denitrifying ruminal bacterium, designated Paenibacillus 79R4 (79R4) intentionally selected for enhanced nitrate- and nitrite-metabolizing ability, on select rumen fermentation characteristics was examined in vivo. Rumen and blood samples were collected from cannulated Holstein steers one day prior to and one day after initiation of treatments applied as three consecutive intra-ruminal administrations of nitrate, to achieve the equivalent of 83 mg sodium nitrate/kg body weight day, given alone or with the nitrite-selected 79R4 (provided to achieve 10⁶ cells/mL rumen fluid). Results revealed a day effect on methane-producing activity, with rates of methane production by ruminal microbes being more rapid when collected one day before than one day after initiation of treatments. Nitrate-metabolizing activity of the rumen microbes was unaffected by day, treatment or their interaction. A day by treatment interaction was observed on nitrite-metabolizing activity, with rates of nitrite metabolism by rumen microbes being most rapid in populations collected one day after initiation of treatment from steers treated with nitrate plus 79R4. A day by treatment interaction was also observed on plasma methemoglobin concentrations, with concentrations being lower from steers one day after initiation of treatments than from collected one day prior to treatment initiation and concentrations being lowest in steers treated with nitrate plus 79R4. A major effect of treatment was observed on accumulations of most prominent and branched chain volatile fatty acids produced and amounts of hexose fermented in the rumen of animals administered nitrate, with concentrations being decreased in steers administered nitrate alone when compared to steers treated with nitrate plus the 79R4. These results demonstrate that the nitrite-selected Paenibacillus 79R4 may help prevent nitrite toxicity in nitrate-treated ruminants while maintaining benefits of reduced methane emissions and preventing inhibition of fermentation efficiency by the microbial ecosystem.

Age-Related Response of Rumen Microbiota to Mineral Salt and Effects of Their Interactions on Enteric Methane Emissions in Cattle

Mineral salt bricks are often used in cow raising as compensation for mineral losses to improve milk yield, growth, and metabolic activity. Generally, effects of minerals are partially thought to result from improvement of microbial metabolism, but their influence on the rumen microbiota has rarely been documented to date. In this study, we investigated the response of microbiota to mineral salt in heifer and adult cows and evaluated ruminal fermentation and enteric methane emissions of cows fed mineral salts. Twelve lactating Holstein cows and twelve heifers fed a total mixed ration (TMR) diet were randomly allocated into two groups, respectively: a treatment group comprising half of the adults and heifers that were fed mineral salt and a control group containing the other half fed a diet with no mineral salt supplement. Enteric methane emissions were reduced by 9.6% (P < 0.05) in adults ingesting a mineral salt diet, while concentrations of ruminal ammonia, butyrate, and propionate were increased to a significant extent (P < 0.05). Enteric methane emissions were also reduced in heifers ingesting a mineral salt diet, but not to a significant extent (P > 0.05). Moreover, the concentrations of ammonia and volatile fatty acids (VFAs) were not significantly altered in heifers (P > 0.05). Based on these results, we performed high-throughput sequencing to explore the bacterial and archaeal communities of the rumen samples. Succiniclasticum and Prevotella, two propionate-producing bacteria, were predominant in samples of both adults and heifers. At the phylotype level, mineral salt intake led to a significant shift from Succiniclasticum to Prevotella and Prevotellaceae populations in adults. In contrast, reduced abundance of Succiniclasticum and Prevotella phylotypes was observed, with no marked shift in propionate-producing bacteria in heifers. Methanogenic archaea were not significantly abundant between groups, either in adult cows or heifers. The shift of Succiniclasticum to Prevotella and Prevotellaceae in adults suggests a response of microbiota to mineral salt that contributes to higher propionate production, which competes for hydrogen utilized by methanogens. Our data collectively indicate that a mineral salt diet can alter interactions of bacterial taxa that result in enteric methane reduction, and this effect is also influenced in an age-dependent manner.

Effect of sole or combined administration of nitrate and 3-nitro-1-propionic acid on fermentation and Salmonella survivability in alfalfa-fed rumen cultures in vitro

Ruminal methanogenesis is a digestive inefficiency resulting in the loss of dietary energy consumed by the host and contributing to environmental methane emission. Nitrate is being investigated as a feed supplement to reduce rumen methane emissions but safety and efficacy concerns persist. To assess potential synergies of co-administering sub-toxic amounts of nitrate and 3-nitro-1-propionate (NPA) on fermentation and Salmonella survivability with an alfalfa-based diet, ruminal microbes were cultured with additions of 8 or 16mM nitrate, 4 or 12mM NPA or their combinations. All treatments decreased methanogenesis compared to untreated controls but volatile fatty acid production and fermentation of hexose were also decreased. Nitrate was converted to nitrite, which accumulated to levels inhibitory to digestion. Salmonella populations were enriched in nitrate only-treated cultures but not in cultures co- or solely treated with NPA. These results reveal a need for dose optimization to safely reduce methane production with forage-based diets.

Rumen methanogens and mitigation of methane emission by anti-methanogenic compounds and substances

Methanogenic archaea reside primarily in the rumen and the lower segments of the intestines of ruminants, where they utilize the reducing equivalents derived from rumen fermentation to reduce carbon dioxide, formic acid, or methylamines to methane (CH₄). Research on methanogens in the rumen has attracted great interest in the last decade because CH₄ emission from ruminants contributes to global greenhouse gas emission and represents a loss of feed energy. Some DNA-based phylogenetic studies have depicted a diverse and dynamic community of methanogens in the rumen. In the past decade, researchers have focused on elucidating the underpinning that determines and affects the diversity, composition, structure, and dynamics of methanogen community of the rumen. Concurrently, many researchers have attempted to develop and evaluate interventions to mitigate enteric CH₄ emission. Although much work has been done using plant secondary metabolites, other approaches such as using nitrate and 3-nitrooxy propanol have also yielded promising results. Most of these antimethanogenic compounds or substances often show inconsistent results among studies and also lead to adverse effects on feed intake and digestion and other aspects of rumen fermentation when fed at doses high enough to achieve effective mitigation. This review provides a brief overview of the rumen methanogens and then an appraisal of most of the antimethanogenic compounds and substances that have been evaluated both in vitro and in vivo. Knowledge gaps and future research needs are also discussed with a focus on methanogens and methane mitigation.

Effects of mineral salt supplement on enteric methane emissions, ruminal fermentation and methanogen community of lactating cows

We evaluated the effects of mineral salt supplement on enteric methane emissions, ruminal fermentation and methanogen community of dairy cows over a whole lactation period. Ten Holstein cows fed a total mixed ration (TMR) diet were randomly allocated into two groups, one supplied with mineral salts as the treatment group and the other as the control group. The methane measurement showed that the ingestion of mineral salts lowered enteric methane emissions significantly (P < 0.05), with an average of 10.5% reduction over the whole lactation period. Ruminal fermentation analysis showed the mineral salt intake could significantly decrease the acetate : propionate ratio (P < 0.05). Real-time PCR assay showed that rumen methanogen abundance significantly reduced in the treatment group (P < 0.05) but was not significantly influenced by mineral salt intake over the whole lactation period. Intergroup methanogen community composition was influenced slightly by mineral salt intake; however, significantly different intragroup profiles were apparent throughout the whole lactation period, according to denaturing gradient gel electrophoresis analysis. In conclusion, these results suggested that the effective mitigation of enteric methane emissions by mineral salt intake could be attributed to decreased density of methanogenic archaea and that fluctuations in methane emission over the lactation period might be related to Methanobrevibacter diversity.

Ruminal Fermentation of Anti-Methanogenic Nitrate- and Nitro-Containing Forages In Vitro

Nitrate, 3-nitro-1-propionic acid (NPA) and 3-nitro-1-propanol (NPOH) can accumulate in forages and be poisonous to animals if consumed in high enough amounts. These chemicals are also recognized as potent anti-methanogenic compounds, but plants naturally containing these chemicals have been studied little in this regard. Presently, we found that nitrate-, NPA-, or NPOH-containing forages effectively decreased methane production, by 35–87%, during in vitro fermentation by mixed cultures of ruminal microbes compared to fermentation by cultures incubated similarly with alfalfa. Methane production was further decreased during the incubation of mixed cultures also inoculated with Denitrobacterium detoxificans, a ruminal bacterium known to metabolize nitrate, NPA, and NPOH. Inhibition of methanogens within the mixed cultures was greatest with the NPA- and NPOH-containing forages. Hydrogen accumulated in all the mixed cultures incubated with forages containing nitrate, NPA or NPOH and was dramatically higher, exceeding 40 μmol hydrogen/mL, in mixed cultures incubated with NPA-containing forage but not inoculated with D. detoxificans. This possibly reflects the inhibition of hydrogenase-catalyzed uptake of hydrogen produced via conversion of 50 μmol added formate per milliliter to hydrogen. Accumulations of volatile fatty acids revealed compensatory changes in fermentation in mixed cultures incubated with the nitrate-, NPA-, and NPOH-containing forages as evidenced by lower accumulations of acetate, and in some cases, higher accumulations of butyrate and lower accumulations of ammonia, iso-buytrate, and iso-valerate compared to cultures incubated with alfalfa. Results reveal that nitrate, NPA, and NPOH that accumulate naturally in forages can be made available within ruminal incubations to inhibit methanogenesis. Further research is warranted to determine if diets can be formulated with nitrate-, NPA-, and NPOH-containing forages to achieve efficacious mitigation in ruminant methane emissions without adversely affecting fermentative efficiency or risking toxicity to animals.

Insights on Alterations to the Rumen Ecosystem by Nitrate and Nitrocompounds

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.

Invited review: Enteric methane in dairy cattle production: quantifying the opportunities and impact of reducing emissions

Many opportunities exist to reduce enteric methane (CH4) and other greenhouse gas (GHG) emissions per unit of product from ruminant livestock. Research over the past century in genetics, animal health, microbiology, nutrition, and physiology has led to improvements in dairy production where intensively managed farms have GHG emissions as low as 1 kg of CO2 equivalents (CO2e)/kg of energy-corrected milk (ECM), compared with >7 kg of CO2 e/kg of ECM in extensive systems. The objectives of this review are to evaluate options that have been demonstrated to mitigate enteric CH4 emissions per unit of ECM (CH4/ECM) from dairy cattle on a quantitative basis and in a sustained manner and to integrate approaches in genetics, feeding and nutrition, physiology, and health to emphasize why herd productivity, not individual animal productivity, is important to environmental sustainability. A nutrition model based on carbohydrate digestion was used to evaluate the effect of feeding and nutrition strategies on CH4/ECM, and a meta-analysis was conducted to quantify the effects of lipid supplementation on CH4/ECM. A second model combining herd structure dynamics and production level was used to estimate the effect of genetic and management strategies that increase milk yield and reduce culling on CH4/ECM. Some of these approaches discussed require further research, but many could be implemented now. Past efforts in CH4 mitigation have largely focused on identifying and evaluating CH4 mitigation approaches based on nutrition, feeding, and modifications of rumen function. Nutrition and feeding approaches may be able to reduce CH4/ECM by 2.5 to 15%, whereas rumen modifiers have had very little success in terms of sustained CH4 reductions without compromising milk production. More significant reductions of 15 to 30% CH4/ECM can be achieved by combinations of genetic and management approaches, including improvements in heat abatement, disease and fertility management, performance-enhancing technologies, and facility design to increase feed efficiency and life-time productivity of individual animals and herds. Many of the approaches discussed are only partially additive, and all approaches to reducing enteric CH4 emissions should consider the economic impacts on farm profitability and the relationships between enteric CH4 and other GHG.

Interactions between microbial consortia in biofilms: a paradigm shift in rumen microbial ecology and enteric methane mitigation

Minimising enteric CH4 emissions from ruminants is a current research priority because CH4 contributes to global warming. The most effective mitigation strategy is to adjust the animal’s diet to complement locally available feed resources so that optimal production is gained from a minimum of animals. This essay concentrates on a second strategy – the use of feed additives that are toxic to methanogens or that redirect H2 (and electrons) to inhibit enteric CH4 emissions from individual animals. Much of the published research in this area is contradictory and may be explained when the microbial ecology of the rumen is considered. Rumen microbes mostly exist in organised consortia within biofilms composed of self-secreted extracellular polymeric substances attached to or within feed particles. In these biofilms, individual colonies are positioned to optimise their use of preferred intermediates from an overall process of organic matter fermentation that generates end-products the animal can utilise. Synthesis of CH4 within biofilms prevents a rise in the partial pressure of H2 (pH2) to levels that inhibit bacterial dehydrogenases, and so reduce fermentation rate, feed intake and digestibility. In this context, hypotheses are advanced to explain changes in hydrogen disposal from the biofilms in the rumen resulting from use of anti-methanogenic feed additives as follows. Nitrate acts as an alternative electron sink when it is reduced via NO2– to NH3 and CH4 synthesis is reduced. However, efficiency of CH4 mitigation is always lower than that predicted and decreases as NO3– ingestion increases. Suggested reasons include (1) variable levels of absorption of NO3–or NO2– from the rumen and (2) increases in H2 production. One suggestion is that NO3– reduction may lower pH2 at the surface of biofilms, thereby creating an ecological niche for growth of syntrophic bacteria that oxidise propionate and/or butyrate to acetate with release of H2. Chlorinated hydrocarbons also inhibit CH4 synthesis and increase H2 and formate production by some rumen methanogens. Formate diffuses from the biofilm and is converted to HCO3– and H2 in rumen fluid and is then excreted via the breath. Short-chain nitro-compounds inhibit both CH4 and formate synthesis when added to ruminal fluid but have little or no effect in redirecting H2 to other sinks, so the pH2 within biofilms may increase to levels that support reductive acetogenesis. Biochar or activated charcoal may also alter biofilm activity and reduce net CH4 synthesis; direct electron transfer between microbes within biofilms may also be involved. A final suggestion is that, during their sessile life stage, protozoa interact with biofilm communities and help maintain pH2 in the biofilm, supporting methanogenesis.

Special topics--Mitigation of methane and nitrous oxide emissions from animal operations: I. A review of enteric methane mitigation options

The goal of this review was to analyze published data related to mitigation of enteric methane (CH4) emissions from ruminant animals to document the most effective and sustainable strategies. Increasing forage digestibility and digestible forage intake was one of the major recommended CH4 mitigation practices. Although responses vary, CH4 emissions can be reduced when corn silage replaces grass silage in the diet. Feeding legume silages could also lower CH4 emissions compared to grass silage due to their lower fiber concentration. Dietary lipids can be effective in reducing CH4 emissions, but their applicability will depend on effects on feed intake, fiber digestibility, production, and milk composition. Inclusion of concentrate feeds in the diet of ruminants will likely decrease CH4 emission intensity (Ei; CH4 per unit animal product), particularly when inclusion is above 40% of dietary dry matter and rumen function is not impaired. Supplementation of diets containing medium to poor quality forages with small amounts of concentrate feed will typically decrease CH4 Ei. Nitrates show promise as CH4 mitigation agents, but more studies are needed to fully understand their impact on whole-farm greenhouse gas emissions, animal productivity, and animal health. Through their effect on feed efficiency and rumen stoichiometry, ionophores are likely to have a moderate CH4 mitigating effect in ruminants fed high-grain or mixed grain-forage diets. Tannins may also reduce CH4 emissions although in some situations intake and milk production may be compromised. Some direct-fed microbials, such as yeast-based products, might have a moderate CH4-mitigating effect through increasing animal productivity and feed efficiency, but the effect is likely to be inconsistent. Vaccines against rumen archaea may offer mitigation opportunities in the future although the extent of CH4 reduction is likely to be small and adaptation by ruminal microbes and persistence of the effect is unknown. Overall, improving forage quality and the overall efficiency of dietary nutrient use is an effective way of decreasing CH4 Ei. Several feed supplements have a potential to reduce CH4 emission from ruminants although their long-term effect has not been well established and some are toxic or may not be economically feasible.

Toxicity and metabolism of nitroalkanes and substituted nitroalkanes

A series of low molecular weight nitro-containing compounds has recently been discovered to have a variety of biological activities including the reduction of anaerobic methane production in ruminant animals and activity against economically important human pathogens, including Salmonella sp. and shigella-toxin producing Escherichia coli . Although some of these nitrocompounds, nitroethane and 2-nitropropane, for example, have been industrial chemicals and synthetic intermediates for years, others such as carboxymethyl nitro-amino acid analogues are new to science and have not been previously described. The purpose of this paper is to review the toxicological profiles, especially as related to events occurring during metabolism and biotransformation, which contribute to toxicological end points of established nitroaliphatic compounds. It is hoped that by summarizing existing knowledge, an understanding of the activities and toxicological profiles of newly established nitrocompounds might be anticipated or adverse events associated with their use might be avoided.

Enteric methane mitigation technologies for ruminant livestock: a synthesis of current research and future directions

Enteric methane (CH(4)) emission in ruminants, which is produced via fermentation of feeds in the rumen and lower digestive tract by methanogenic archaea, represents a loss of 2% to 12% of gross energy of feeds and contributes to global greenhouse effects. Globally, about 80 million tonnes of CH(4) is produced annually from enteric fermentation mainly from ruminants. Therefore, CH(4) mitigation strategies in ruminants have focused to obtain economic as well as environmental benefits. Some mitigation options such as chemical inhibitors, defaunation, and ionophores inhibit methanogenesis directly or indirectly in the rumen, but they have not confirmed consistent effects for practical use. A variety of nutritional amendments such as increasing the amount of grains, inclusion of some leguminous forages containing condensed tannins and ionophore compounds in diets, supplementation of low-quality roughages with protein and readily fermentable carbohydrates, and addition of fats show promise for CH(4) mitigation. These nutritional amendments also increase the efficiency of feed utilization and, therefore, are most likely to be adopted by farmers. Several new potential technologies such as use of plant secondary metabolites, probiotics and propionate enhancers, stimulation of acetogens, immunization, CH(4) oxidation by methylotrophs, and genetic selection of low CH(4)-producing animals have emerged to decrease CH(4) production, but these require extensive research before they can be recommended to livestock producers. The use of bacteriocins, bacteriophages, and development of recombinant vaccines targeting archaeal-specific genes and cell surface proteins may be areas worthy of investigation for CH(4) mitigation as well. A combination of different CH(4) mitigation strategies should be adopted in farm levels to substantially decrease methane emission from ruminants. Evidently, comprehensive research is needed to explore proven and reliable CH(4) mitigation technologies that would be practically feasible and economically viable while improving ruminant production.

Effects of feed-supplementation and hide-spray application of two sources of tannins on enteric and hide bacteria of feedlot cattle

Pathogenic bacteria attached to the hide or shed in the feces of cattle at slaughter can contaminate carcasses intended to be processed for human consumption. Therefore, new pre-harvest interventions are needed to prevent the carriage and excretion of foodborne pathogens in cattle presented to the processing plant. The objectives of this study were to examine the antimicrobial effects of hydrolysable tannin-rich chestnut and condensed tannin-rich mimosa extracts on bacterial indicators of foodborne pathogens when applied as a hide-intervention and as a feed additive to feedlot cattle. Water (control) or solutions (3 % wt/vol) of chestnut- and mimosa-extract treatments were sprayed (25 mL) at the left costal side of each animal to a 1000 cm² area, divided in four equal quadrants. Hide-swabs samples obtained at pre-, 2-min, 8-h, and 24-h post-spray application were cultured to enumerate Escherichia coli/total coliforms and total aerobic plate counts. In a second experiment, diets supplemented without (controls) or with (1.5 % of diet dry matter) chestnut- or mimosa-extracts were fed during a 42-day experimental feeding period. Weekly fecal samples starting on day 0, and rumen fluid obtained on days 0, 7, 21 or 42 were cultured to enumerate E.coli/total coliforms and Campylobacter. Tannin spray application showed no effect of treatment or post-application-time (P > 0.05) on measured bacterial populations, averaging 1.7/1.8, 1.5/1.6 and 1.5/1.7 (log₁₀CFU/cm²) for E. coli/total coliforms, and 4.0, 3.4 and 4.2 (log₁₀CFU/cm²) in total aerobes for control, chestnut and mimosa treatments, respectively. Mean (± SEM) ruminal E. coli and total coliform concentrations (log(10) CFU/mL) were reduced (P < 0.01) in steers fed chestnut-tannins (3.6 and 3.8 ± 0.1) in comparison with the controls (4.1 and 4.2 ± 0.1). Fecal E. coli concentrations were affected by treatment (P< 0.01), showing the highest values (log₁₀ CFU/g) in fecal contents from mimosa-fed steers compared to controls (5.9 versus 5.6 ± 0.1 SEM, respectively). Total coliforms (log CFU/g) showed the highest values (P < 0.01) in feces from chestnut- and mimosa-fed steers (6.0 and 6.1 ± 0.1 respectively) in comparison with controls (5.7 ± 0.1). Fecal Campylobacter concentrations (log₁₀CFU/g) were affected by treatment (P < 0.05), day (P < 0.001) and their interaction (P < 0.01) with the controls having lower concentrations than chestnut- and mimosa-fed steers (0.4, 1.0, and 0.8 ± 0.3, respectively). It was concluded that under our research conditions, tannins were not effective in decreasing measured bacterial populations on beef cattle hides. Additionally, chestnut tannin reduced E. coli and total coliforms within the rumen but the antimicrobial effect was not maintained in the lower gastrointestinal tract. Further research is necessary to elucidate the possible antimicrobial effects of tannins at site-specific locations of the gastrointestinal tract in beef cattle fed high-grain and high-forage diets.

Chemical treatment of animal feed and water for the control of Salmonella

The control of Salmonella in animal feedstuffs is important, principally to protect the human food chain from contamination by Salmonella derived from infected animals. The transmission of Salmonella from animal feeds to animals, and onward to human food products, has been convincingly documented. This is especially important for chicken breeding and laying flocks and pigs, in view of the consequences of recent or imminent control legislation in the European Union. Animal feed ingredients, particularly animal and plant-derived protein meals, are frequently contaminated with Salmonella either from source or from processing plant, and recontamination in compounding mills is an additional problem. Several complementary strategies have been used to control this feed contamination, and these include a range of chemical treatments. The principal agents used are as follows: organic acids and their salts, formaldehyde, and bacterial membrane disruptors such as terpenes and essential oils. Experimental agents include chlorate compounds. Many products use blends of agents from the same or different chemical groups to achieve synergistic or combination effects. The present review draws upon published and company data to describe the various modes of action and efficacies of different chemical agents delivered in feed or in drinking water against Salmonella occurring in feed or in livestock environments. Reasons for the failure of protection are explored, along with problems in usage such as corrosion and reduced palatability. Given the wide array of products available with contrasting modes of action, the need for standardized tests of efficacy is also discussed.

Effects of select nitrocompounds on in vitro ruminal fermentation during conditions of limiting or excess added reductant

Ruminal methane (CH(4)) production results in the loss of up to 12% of gross energy intake and contributes nearly 20% of the United States' annual emission of this greenhouse gas. We report the effects of select nitrocompounds on ruminal fermentation after 22 h in vitro incubation (39 degrees C) with or without additions of hydrogen (H(2)), formate or both. In incubations containing no added reductant, CH(4) production was inhibited 41% by 2-nitro-1-propanol (2NPOH) and >97% by 3-nitro-1-propionic acid (3NPA), nitroethane (NE) and 2-nitroethanol (2NEOH) compared to non-treated controls and H(2) did not accumulate. With formate as the sole added reductant, nitro-treatment reduced CH(4) production by >99% and caused 42% to complete inhibition of formate catabolism compared to controls, and the accumulation of H(2) increased slightly. Nitro-treatment decreased CH(4) production 57-98% from that of controls when supplied H(2) or formate plus H(2). Formate catabolism was decreased 42-84% from that in controls by all nitro-treatments except 3NPA with both formate and H(2). Greater than 97% of the added H(2) was catabolized within controls; >84% was catabolized in nitro-treated incubations. Acetate, propionate and butyrate accumulations were unaffected by nitro-treatment irregardless of reductant; however, effects on ammonia and branched chain fatty acid accumulations varied. These results suggest that nitro-treatment inhibited formate dehydrogenase/formate hydrogen lyase and hydrogenase activity.

Incidence and ecology of Campylobacter jejuni and coli in animals

Since its initial emergence in the 1970s, Campylobacter has become one of the most common causative agents of bacterial foodborne illness. Campylobacter species readily colonize the gastrointestinal tracts of domestic, feral and wild animals and while they rarely cause clinical disease in food animals, they can produce severe acute gastroenteritis in humans. Prevalence of Campylobacter in food animals can exceed 80% thus challenging processors to employ post-harvest pathogen reduction strategies. Reduction of pathogens before arrival to the abattoir is also of interest because the implementation of pre-harvest interventions may compliment existing post-harvest control techniques to further diminish possible retail sources of infection. Such multiple hurdle approaches that simultaneously utilize pre- and post-harvest control techniques are expected to be the most effective approach for decreasing human illness associated with foodborne pathogens.

Effects of nitroethane and monensin on ruminal fluid fermentation characteristics and nitrocompound-metabolizing bacterial populations

Nitroethane is a potent inhibitor of ruminal CH 4 production, a digestive inefficiency resulting in the loss of 2-15% of a ruminant's gross energy intake and an important emission source of this greenhouse gas. To assess the effect of nitroethane on methanogenesis and characterize ruminal adaptation observed with low treatment doses to this inhibitor, ruminal microbes were cultured in vitro with supplements of water (controls), 4.5 and 9 mM nitroethane, and 0.09 mM monensin, with or without 9 mM nitroethane. All treatments decreased CH 4 production >78% compared to controls; however, differential effects of treatments were observed on CO 2, butyrate isobutyrate, and valerate production. Treatments did not affect H 2 accumulation or acetate and propionate production. Most probable numbers of nitrometabolizing bacteria were increased with 4.5 and 9 mM nitroethane compared to numbers recovered from controls or monensin-containing treatments, which may explain ruminal adaptation to lower nitroethane treatments.