A review of feeding supplementary nitrate to ruminant animals: nitrate toxicity, methane emissions, and production performance

Feed additives for methane mitigation: Recommendations for testing enteric methane-mitigating feed additives in ruminant studies

There is a need for rigorous and scientifically-based testing standards for existing and new enteric methane mitigation technologies, including antimethanogenic feed additives (AMFA). The current review provides guidelines for conducting and analyzing data from experiments with ruminants intended to test the antimethanogenic and production effects of feed additives. Recommendations include study design and statistical analysis of the data, dietary effects, associative effect of AMFA with other mitigation strategies, appropriate methods for measuring methane emissions, production and physiological responses to AMFA, and their effects on animal health and product quality. Animal experiments should be planned based on clear hypotheses, and experimental designs must be chosen to best answer the scientific questions asked, with pre-experimental power analysis and robust post-experimental statistical analyses being important requisites. Long-term studies for evaluating AMFA are currently lacking and are highly needed. Experimental conditions should be representative of the production system of interest, so results and conclusions are applicable and practical. Methane-mitigating effects of AMFA may be combined with other mitigation strategies to explore additivity and synergism, as well as trade-offs, including relevant manure emissions, and these need to be studied in appropriately designed experiments. Methane emissions can be successfully measured, and efficacy of AMFA determined, using respiration chambers, the sulfur hexafluoride method, and the GreenFeed system. Other techniques, such as hood and face masks, can also be used in short-term studies, ensuring they do not significantly affect feed intake, feeding behavior, and animal production. For the success of an AMFA, it is critically important that representative animal production data are collected, analyzed, and reported. In addition, evaluating the effects of AMFA on nutrient digestibility, animal physiology, animal health and reproduction, product quality, and how AMFA interact with nutrient composition of the diet is necessary and should be conducted at various stages of the evaluation process. The authors emphasize that enteric methane mitigation claims should not be made until the efficacy of AMFA is confirmed in animal studies designed and conducted considering the guidelines provided herein.

Feed additives for methane mitigation: A guideline to uncover the mode of action of antimethanogenic feed additives for ruminants

This publication aims to provide guidelines of the knowledge required and the potential research to be conducted in order to understand the mode of action of antimethanogenic feed additives (AMFA). In the first part of the paper, we classify AMFA into 4 categories according to their mode of action: (1) lowering dihydrogen (H2) production; (2) inhibiting methanogens; (3) promoting alternative H2-incorporating pathways; and (4) oxidizing methane (CH4). The second part of the paper presents questions that guide the research to identify the mode of action of an AMFA on the rumen CH4 production from 5 different perspectives: (1) microbiology; (2) cell and molecular biochemistry; (3) microbial ecology; (4) animal metabolism; and (5) cross-cutting aspects. Recommendations are provided to address various research questions within each perspective, along with examples of how aspects of the mode of action of AMFA have been elucidated before. In summary, this paper offers timely and comprehensive guidelines to better understand and reveal the mode of action of current and emerging AMFA.

Effects of dose, dietary nutrient composition, and supplementation period on the efficacy of methane mitigation strategies in dairy cows: A meta-analysis

The objective of this meta-analysis was to quantify the potential of CH4-mitigating strategies in dairy cattle when accounting for the effects of treatment dose, dietary nutrient composition, and supplementation period. Data from 218 studies with dairy cattle published between 1963 to 2022 were reviewed. Individual CH4 mitigation strategies selected for the analysis were algae (Asparagopsis spp.), 3-nitrooxypropanol, nitrate, lipids, plant secondary compounds, and direct-fed microbials (DFM). Response variables evaluated were daily CH4 emission (g/d), CH4 yield (g CH4/kg DMI), and CH4 intensity (g CH4/kg milk yield [MY] and ECM). Relative mean difference between treatment and control means reported in the studies were calculated and used in the statistical analysis. Robust variance estimation method was used to analyze the effects of CH4 mitigation strategies. Dose, forage-to-concentrate ratio (F:C), dietary concentrations of CP, ether extract (EE), NDF, ADF, and starch, and supplementation period were used as continuous explanatory variables. Data for algae supplementation were limited and responses to studied species were contrasting but, overall, Asparagopsis spp. effectively decreased daily CH4 emission, CH4 yield, and CH4 intensities by 29.8 ± 4.6%, 23.0 ± 5.3%, 34.0 ± 4.3%, and 22.6 ± 7.3%, respectively. Supplementation of 3-nitrooxypropanol decreased daily CH4 emission, yield, and intensity (per kg MY and ECM) by 28.2 ± 3.6%, 28.7 ± 2.8%, 29.2 ± 3.1%, and 31.8 ± 2.8%, respectively, compared with control. Decreasing dietary fiber (i.e., F:C, NDF, and ADF), whereas increasing dietary starch concentration increased the efficacy of 3-nitrooxypropanol at mitigating enteric CH4 emission. Nitrate supplementation decreased CH4 emission, yield, and intensity (per kg ECM) by 18.5% ± 1.9%, 17.6 ± 1.6%, and 13.0 ± 0.2%, respectively, compared with control. Efficacy of nitrate at mitigating enteric CH4 yield and CH4 intensity was positively associated with dose, and efficacy of nitrate at mitigating CH4 yield was positively associated with dietary starch concentration. Lipid supplementation decreased CH4 emission, yield, and intensities by up to 14.8 ± 2.3%, respectively, compared with control. Efficacy of lipids supplementation was positively associated with dietary EE, starch, and supplementation period, but negatively associated with dietary ADF concentration. Free oil supplementation tended to increase lipid efficacy by 31% at decreasing CH4 emission, compared with control. Condensed tannins and plant-derived bioactive compounds decreased CH4 yield by 11.3 ± 2.9% and 5.7 ± 2.5%, respectively, but oregano did not affect enteric CH4 emission metrics in the current meta-analysis. Direct-fed microbials were not effective in mitigating enteric CH4 emission variables. Data were limited to determine the effects of dietary nutrients and duration of supplementation on efficacy of Asparagopsis spp., plant secondary compounds and DFM. Overall, supplementation of the diet with Asparagopsis spp., 3-nitrooxypropanol, nitrate, and lipids were the most effective strategies for decreasing enteric CH4 emission in dairy cattle. Variability in the efficacy of most CH4 mitigation strategies can be partially explained by differences in treatment dose, dietary nutrient composition, and supplementation period.

Perovskite Oxides: Syntheses and Perspectives on Their Application for Nitrate Reduction

Over the decades, the rise in nitrate levels in the ecosystem has posed a serious threat to the continuous existence of humans, fauna, and flora. The deleterious effects of increasing levels of nitrates in the ecosystem have led to adverse health and environmental implications in the form of methemoglobinemia and eutrophication, respectively. Different pathways/routes for the syntheses of perovskites and their oxides were presented in this review. In recent times, electrocatalytic reduction has emerged as the most utilized technique for the conversion of nitrates into ammonia, an industrial feedstock. According to published papers, the efficiency of various perovskites and their oxides used for the electrocatalytic reduction of nitrate achieved a high Faradaic efficiency of 98%. Furthermore, studies published have shown that there is a need to improve the chemical stability of perovskites and their oxides during scale-up applications, as well as their scalability for industrial applications.

Can freshwater plants and algae act as an effective feed supplement to reduce methane emissions from ruminant livestock?

Methane production by livestock is a substantial component of greenhouse gas emissions worldwide. The marine red algae, Asparagopsis taxiformis, has been identified as a possible supplement in livestock feeds due to its potent inhibition of methane production but currently is unable to be produced at scale. Finding additional taxa that inhibit methane production is therefore desirable. Here we provide foundational evidence of methanogenesis-inhibiting properties in Australian freshwater plants and algae, reviewing candidate species and testing species' chemical composition and efficacy in vitro. Candidate plant species and naturally-occurring algal mixes were collected and assessed for ability to reduce methane in batch testing and characterised for biochemical composition, lipids and fatty acids, minerals and DNA. We identified three algal mixes and one plant (Montia australasica) with potential to reduce methane yield in in vitro batch assay trials. All three algal mixes contained Spirogyra, although additional testing would be needed to confirm this alga was responsible for the observed activity. For the two samples that underwent multiple dose testing, Algal mix 1 (predominantly Spirogyra maxima) and M. australasica, there seems to be an optimum dose but sources, harvesting and storage conditions potentially determine their methanogenesis-inhibiting activity. Based on their compositions, fatty acids are likely to be acting to reduce methane in Algal mix 1 while M. australasica likely contains substantial amounts of the flavonoids apigenin and kaempferol, which are associated with methane reduction. Based on their mineral composition, the samples tested would be safe for livestock consumption at an inclusion rate of 20%. Thus, we identified multiple Australian species that have potential to be used as a feed supplement to reduce methane yield in livestock which may be suitable for individual farmers to grow and feed, reducing complexities of supply associated with marine alternatives and suggesting avenues for investigation for similar species elsewhere.

Recent Advances in Enteric Methane Mitigation and the Long Road to Sustainable Ruminant Production

Mitigation of methane emission, a potent greenhouse gas, is a worldwide priority to limit global warming. A substantial part of anthropogenic methane is emitted by the livestock sector, as methane is a normal product of ruminant digestion. We present the latest developments and challenges ahead of the main efficient mitigation strategies of enteric methane production in ruminants. Numerous mitigation strategies have been developed in the last decades, from dietary manipulation and breeding to targeting of methanogens, the microbes that produce methane. The most recent advances focus on specific inhibition of key enzymes involved in methanogenesis. But these inhibitors, although efficient, are not affordable and not adapted to the extensive farming systems prevalent in low- and middle-income countries. Effective global mitigation of methane emissions from livestock should be based not only on scientific progress but also on the feasibility and accessibility of mitigation strategies.

A Review of Potential Feed Additives Intended for Carbon Footprint Reduction through Methane Abatement in Dairy Cattle

Eight rumen additives were chosen for an enteric methane-mitigating comparison study including garlic oil (GO), nitrate, Ascophyllum nodosum (AN), Asparagopsis (ASP), Lactobacillus plantarum (LAB), chitosan (CHI), essential oils (EOs) and 3-nitrooxypropanol (3-NOP). Dose-dependent analysis was carried out on selected feed additives using a meta-analysis approach to determine effectiveness in live subjects or potential efficacy in live animal trials with particular attention given to enteric gas, volatile fatty acid concentrations, and rumen microbial counts. All meta-analysis involving additives GO, nitrates, LAB, CHI, EOs, and 3-NOP revealed a reduction in methane production, while individual studies for AN and ASP displayed ruminal bacterial community improvement and a reduction in enteric CH4. Rumen protozoal depression was observed with GO and AN supplementation as well as an increase in propionate production with GO, LAB, ASP, CHI, and 3-NOP rumen fluid inoculation. GO, AN, ASP, and LAB demonstrated mechanisms in vitro as feed additives to improve rumen function and act as enteric methane mitigators. Enzyme inhibitor 3-NOP displays the greatest in vivo CH4 mitigating capabilities compared to essential oil commercial products. Furthermore, this meta-analysis study revealed that in vitro studies in general displayed a greater level of methane mitigation with these compounds than was seen in vivo, emphasising the importance of in vivo trials for final verification of use. While in vitro gas production systems predict in vivo methane production and fermentation trends with reasonable accuracy, it is necessary to confirm feed additive rumen influence in vivo before practical application.

Distinct microbial hydrogen and reductant disposal pathways explain interbreed variations in ruminant methane yield

Ruminants are essential for global food security, but these are major sources of the greenhouse gas methane. Methane yield is controlled by the cycling of molecular hydrogen (H2), which is produced during carbohydrate fermentation and is consumed by methanogenic, acetogenic, and respiratory microorganisms. However, we lack a holistic understanding of the mediators and pathways of H2 metabolism and how this varies between ruminants with different methane-emitting phenotypes. Here, we used metagenomic, metatranscriptomic, metabolomics, and biochemical approaches to compare H2 cycling and reductant disposal pathways between low-methane-emitting Holstein and high-methane-emitting Jersey dairy cattle. The Holstein rumen microbiota had a greater capacity for reductant disposal via electron transfer for amino acid synthesis and propionate production, catalyzed by enzymes such as glutamate synthase and lactate dehydrogenase, and expressed uptake [NiFe]-hydrogenases to use H2 to support sulfate and nitrate respiration, leading to enhanced coupling of H2 cycling with less expelled methane. The Jersey rumen microbiome had a greater proportion of reductant disposal via H2 production catalyzed by fermentative hydrogenases encoded by Clostridia, with H2 mainly taken up through methanogenesis via methanogenic [NiFe]-hydrogenases and acetogenesis via [FeFe]-hydrogenases, resulting in enhanced methane and acetate production. Such enhancement of electron incorporation for metabolite synthesis with reduced methanogenesis was further supported by two in vitro measurements of microbiome activities, metabolites, and public global microbiome data of low- and high-methane-emitting beef cattle and sheep. Overall, this study highlights the importance of promoting alternative H2 consumption and reductant disposal pathways for synthesizing host-beneficial metabolites and reducing methane production in ruminants.

Impact of Supplementing a Backgrounding Diet with Nonprotein Nitrogen on In Vitro Methane Production, Nutrient Digestibility, and Steer Performance

Two experiments were conducted to evaluate the effect of nonprotein nitrogen (NPN) supplementation on in vitro fermentation and animal performance using a backgrounding diet. In experiment 1, incubations were conducted on three separate days (replicates). Treatments were control (CTL, without NPN), urea (U), urea-biuret (UB), and urea-biuret-nitrate (UBN) mixtures. Except for control, treatments were isonitrogenous using 1% U inclusion as a reference. Ruminal fluid was collected from two Angus-crossbred steers fed a backgrounding diet plus 100 g of a UBN mixture for at least 35 d. The concentration of volatile fatty acids (VFA) and ammonia nitrogen (NH3-N), in vitro organic matter digestibility (IVOMD), and total gas and methane (CH4) production were determined at 24 h of incubation. In experiment 2, 72 Angus-crossbred yearling steers (303 ± 29 kg of body weight [BW]) were stratified by BW and randomly allocated in nine pens (eight animals/pen and three pens/treatment). Steers consumed a backgrounding diet formulated to match the diet used in the in vitro fermentation experiment. Treatments were U, UB, and UBN and were isonitrogenous using 1% U inclusion as a reference. Steers were adapted to the NPN supplementation for 17 d. Then, digestibility evaluation was performed after 13 d of full NPN supplementation for 4 d using 36 steers (12 steers/treatment). After that, steer performance was evaluated for 56 d (24 steers/treatment). In experiment 1, NPN supplementation increased the concentration of NH3-N and VFA (P < 0.01) without affecting the IVOMD (P = 0.48), total gas (P = 0.51), and CH4 production (P = 0.57). Additionally, in vitro fermentation parameters did not differ (P > 0.05) among NPN sources. In experiment 2, NPN supplementation did not change dry matter and nutrient intake (P > 0.05). However, UB and UBN showed lower (P < 0.05) nutrient digestibility than U, except for starch (P = 0.20). Dry matter intake (P = 0.28), average daily gain (P = 0.88), and gain:feed (P = 0.63) did not differ among steers receiving NPN mixtures. In conclusion, tested NPN mixtures have the potential to be included in the backgrounding diets without any apparent negative effects on animal performance and warrant further studies to evaluate other variables to fully assess the response of feeding these novel NPN mixtures.

Feasibility of mitigation measures for agricultural greenhouse gas emissions in the UK. A systematic review

The UK Government has set an ambitious target of achieving a national "net-zero" greenhouse gas economy by 2050. Agriculture is arguably placed at the heart of achieving net zero, as it plays a unique role as both a producer of GHG emissions and a sector that has the capacity via land use to capture carbon (C) when managed appropriately, thus reducing the concentration of carbon dioxide (CO2) in the atmosphere. Agriculture's importance, particularly in a UK-specific perspective, which is also applicable to many other temperate climate nations globally, is that the majority of land use nationwide is allocated to farming. Here, we present a systematic review based on peer-reviewed literature and relevant "grey" reports to address the question "how can the agricultural sector in the UK reduce, or offset, its direct agricultural emissions at the farm level?" We considered the implications of mitigation measures in terms of food security and import reliance, energy, environmental degradation, and value for money. We identified 52 relevant studies covering major foods produced and consumed in the UK. Our findings indicate that many mitigation measures can indeed contribute to net zero through GHG emissions reduction, offsetting, and bioenergy production, pending their uptake by farmers. While the environmental impacts of mitigation measures were covered well within the reviewed literature, corresponding implications regarding energy, food security, and farmer attitudes towards adoption received scant attention. We also provide an open-access, informative, and comprehensive dataset for agri-environment stakeholders and policymakers to identify the most promising mitigation measures. This research is of critical value to researchers, land managers, and policymakers as an interim guideline resource while more quantitative evidence becomes available through the ongoing lab-, field-, and farm-scale trials which will improve the reliability of agricultural sustainability modelling in the future.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13593-023-00938-0.

Dynamics of in vitro rumen methane production after nitrate addition

The present study aimed to assess the dynamics of rumen methane (CH4) production following the addition of NaNO3. This was done using an in vitro rumen fermentation system that ensures continuous gas and methane assessments. Four different levels of NaNO3 were used to get the final nitrate concentrations of 0.5, 1.0, 1.5, and 2.0 mg/ml of rumen fluid. For each dose, corresponding controls contained sodium chloride and urea were realised to ensure comparable levels of sodium and nitrogen. The addition of nitrates had slight effect on the intensity of fermentation because the total gas produced minus CH4 (total methane-free gas) only went down at the highest dose (2.0 mg/ml), and the final concentrations of SCFA were the same at all doses. The most evident effect was a modification of the SCFA profile (low concentrations of propionate and valerate, progressive increments of acetate, and decreases of butyrate) and a reduction in overall CH4 production. The CH4 yield for the 0.5 mg/ml dose was not different from control in the entire fermentation. Yield of the 1.0 mg/ml dose was significantly lower than the control group (p < 0.05) only within the initial 24-h period, and higher dosages (1.5 and 2.0 mg/ml) were lower during the entire fermentation (p < 0.01). Methane yields were well fitted with the Gompertz model, but only the highest level of nitrate inclusion had a significant impact on the majority of model parameters (p < 0.01). The linear regressions between CH4 yields (y) and the amounts of nitrates (x) at progressive fermentation durations (e.g. 6, 12, 24, and 48 h) produced equations with increasing absolute slopes (from -0.069 to -0.517 ml/mg of nitrate). Therefore, nitrate reduced rumen CH4 yield in a dose-dependent manner: the impact of low doses was primarily observed at the initial stages of fermentation, whereas high doses exhibited effectiveness throughout the entire fermentation process. In conclusion, in batch fermentation systems, the dose effect of nitrates on methane yield was time dependent.

Effect of nitrate supplementation, dietary protein supply, and genetic yield index on performance, methane emission, and nitrogen efficiency in dairy cows

The objective was to investigate the effect of nonprotein nitrogen source, dietary protein supply, and genetic yield index on methane emission, N metabolism, and ruminal fermentation in dairy cows. Forty-eight Danish Holstein dairy cows (24 primiparous cows and 24 multiparous cows) were used in a 6 × 4 incomplete Latin square design with 4 periods of 21-d duration. Cows were fed ad libitum with the following 6 experimental diets: diets with low, medium, or high rumen degradable protein (RDP):rumen undegradable protein (RUP) ratio (manipulated by changing the proportion of corn meal, corn gluten meal, and corn gluten feed) combined with either urea or nitrate (10 g NO₃^-/kg of dry matter) as nonprotein nitrogen source. Samples of ruminal fluid and feces were collected from multiparous cows, and total-tract nutrient digestibility was estimated using TiO₂ as flow marker. Milk samples were collected from all 48 cows. Gas emission (CH₄, CO₂, and H₂) was measured by 4 GreenFeed units. We observed no significant interaction between dietary RDP:RUP ratio and nitrate supplementation, and between nitrate supplementation and genetic yield index on CH₄ emission (production, yield, intensity). As dietary RDP:RUP ratio increased, intake of crude protein, RDP, and neutral detergent fiber and total-tract digestibility of crude protein linearly increased, and RUP intake linearly decreased. Yield of milk, energy-corrected milk, and milk protein and lactose linearly decreased, whereas milk fat and milk urea nitrogen concentrations linearly increased as dietary RDP:RUP ratio increased. The increase in dietary RDP:RUP ratio resulted in a linear increase in the excretion of total purine derivatives and N in urine, but a linear decrease in N efficiency (milk N in % of N intake). Nitrate supplementation reduced dry matter intake (DMI) and increased total-tract organic matter digestibility compared with urea supplementation. Nitrate supplementation resulted in a greater reduction in DMI and daily CH₄ production and a greater increase in daily H₂ production in multiparous cows compared with primiparous cows. Nitrate supplementation also showed a greater reduction in milk protein and lactose yield in multiparous cows than in primiparous cows. Milk protein and lactose concentrations were lower for cows receiving nitrate diets compared with cows receiving urea diets. Nitrate supplementation reduced urinary purine derivatives excretion from the rumen, whereas N efficiency tended to increase. Nitrate supplementation reduced proportion of acetate and propionate in ruminal volatile fatty acids. In conclusion, no interaction was observed between dietary RDP:RUP ratio and nitrate supplementation, and no interaction between nitrate supplementation and genetic yield index on CH₄ emission (production, yield, intensity) was noted. Nitrate supplementation resulted in a greater reduction in DMI and CH₄ production, and a greater increase in H₂ production in multiparous cows than in primiparous cows. As the dietary RDP:RUP ratio increased, CH₄ emission was unaffected and RDP intake increased, but RUP intake and milk yield decreased. Genetic yield index did not affect CH₄ production, yield, or intensity.

Review: Reducing enteric methane emissions improves energy metabolism in livestock: is the tenet right?

The production of enteric methane in the gastrointestinal tract of livestock is considered as an energy loss in the equations for estimating energy metabolism in feeding systems. Therefore, the spared energy resulting from specific inhibition of methane emissions should be re-equilibrated with other factors of the equation. And, it is commonly assumed that net energy from feeds increases, thus benefitting production functions, particularly in ruminants due to the important production of methane in the rumen. Notwithstanding, we confirm in this work that inhibition of emissions in ruminants does not transpose into consistent improvements in production. Theoretical calculations of energy flows using experimental data show that the expected improvement in net energy for production is small and difficult to detect under the prevailing, moderate inhibition of methane production (≈25%) obtained using feed additives inhibiting methanogenesis. Importantly, the calculation of energy partitioning using canonical models might not be adequate when methanogenesis is inhibited. There is a lack of information on various parameters that play a role in energy partitioning and that may be affected under provoked abatement of methane. The formula used to calculate heat production based on respiratory exchanges should be validated when methanogenesis is inhibited. Also, a better understanding is needed of the effects of inhibition on fermentation products, fermentation heat, and microbial biomass. Inhibition induces the accumulation of H2, the main substrate used to produce methane, that has no energetic value for the host, and it is not extensively used by the majority of rumen microbes. Currently, the fate of this excess of H2 and its consequences on the microbiota and the host are not well known. All this additional information will provide a better account of energy transactions in ruminants when enteric methanogenesis is inhibited. Based on the available information, it is concluded that the claim that enteric methane inhibition will translate into more feed-efficient animals is not warranted.

Invited review: Rumen modifiers in today's dairy rations

Our aim was to review feed additives that have a potential ruminal mechanism of action when fed to dairy cattle. We discuss how additives can influence ruminal fermentation stoichiometry through electron transfer mechanisms, particularly the production and usage of dihydrogen. Lactate accumulation should be avoided, especially when acidogenic conditions suppress ruminal neutral detergent fiber digestibility or lead to subclinical acidosis. Yeast products and other probiotics are purported to influence lactate uptake, but growing evidence also supports that yeast products influence expression of gut epithelial genes promoting barrier function and resulting inflammatory responses by the host to various stresses. We also have summarized methane-suppressing additives for potential usage in dairy rations. We focused on those with potential to decrease methane production without decreasing fiber digestibility or milk production. We identified some mitigating factors that need to be addressed more fully in future research. Growth factors such as branched-chain volatile fatty acids also are part of crucial cross-feeding among groups of microbes, particularly to optimize fiber digestibility in the rumen. Our developments of mechanisms of action for various rumen-active modifiers should help nutrition advisors anticipate when a benefit in field conditions is more likely.

In vitro screening of anti-methanogenic additives for use in Australian grazing systems

Despite considerable effort to develop and optimise additives to reduce methane emissions from cattle, little information on additive effectiveness exists for cattle under grazing scenarios. As the majority of Australian cattle production occurs on grazing land it is pertinent to report on the use of additives under simulated conditions. The current study evaluated the addition of nine additives to Rhodes grass hay under in vitro conditions, to estimate their impact on methane (CH4), gas production, and rumen fermentation parameters (volatile fatty acids, rumen pH and in vitro dry matter digestibility [IVDMD]). Citral extract at 0.1% of rumen media decreased all CH4 production parameters, but reduced gas production and digestibility, compared to a 100% hay control. Similarly, Sandalwood essential oil decreased CH4 production at 48 h, IVDMD and gas production, compared to the control. Biochar + nitrates at 5 and 8% DM, and Biochar + Asparagopsis at 5% DM decreased cumulative CH4 production (15.6%, 25.9%, 23.8%, respectively; P &lt; 0.01), compared to the control. No changes in IVDMD and gas production were observed. As such, the biochar additives were considered the most promising additives from those evaluated with a substrate designed to replicate Australian grazing systems.

The Effects of N Enrichment on Microbial Cycling of Non-CO2 Greenhouse Gases in Soils-a Review and a Meta-analysis

Terrestrial ecosystems are typically nitrogen (N) limited, but recent years have witnessed N enrichment in various soil ecosystems caused by human activities such as fossil fuel combustion and fertilizer application. This enrichment may alter microbial processes in soils in a way that would increase the emissions of methane (CH₄) and nitrous oxide (N₂O), thereby aggravating global climate change. This review focuses on the effects of N enrichment on methanogens and methanotrophs, which play a central role in the dynamics of CH₄ at the global scale. We also address the effects of N enrichment on N₂O, which is produced in soils mainly by nitrification and denitrification. Overall, N enrichment inhibits methanogenesis in pure culture experiments, while its effects on CH₄ oxidation are more complicated. The majority of previous studies reported that N enrichment, especially NH₄⁺ enrichment, inhibits CH₄ oxidation, resulting in higher CH₄ emissions from soils. However, both activation and neutral responses have also been reported, particularly in rice paddies and landfill sites, which is well reflected in our meta-analysis. In contrast, N enrichment substantially increases N₂O emission by both nitrification and denitrification, which increases proportionally to the amount of N amended. Future studies should address the effects of N enrichment on the active microbes of those functional groups at multiple scales along with parameterization of microbial communities for the application to climate models at the global scale.

Encapsulated nitrate replacing soybean meal in diets with and without monensin on in vitro ruminal fermentation

This study assessed the association between encapsulated nitrate product (ENP) and monensin (MON) to mitigate enteric methane (CH4) in vitro and possible effects on ruminal degradability, enteric fermentation characteristics, and microbial populations. Six treatments were used in randomized complete design in a 2×3 factorial arrangement with two levels of MON (0 and 2.08 mg/mL of buffered rumen fluid) and three levels of ENP (0, 1.5 and 3.0%). The substrate consisted of 50% Tifton-85 hay and 50% concentrate mixture (ground corn and soybean meal). ENP replaced soybean meal to achieve isonitrogenous diets (15% CP). No ENP×MON interaction was observed for any measured variable (P > 0.05) except for the relative abundance of F. succinogenes (P = 0.02) that linearly increased in diets with MON when ENP was added. The ENP addition decreased CH4 production (P < 0.01) without affecting (P > 0.05) truly degraded organic matter nor the relative abundance of methanogens. Hydrogen production was reduced with MON (P = 0.04) and linearly decreased with ENP inclusion (P = 0.02). We concluded that use of nitrate is a viable strategy for CH4 reduction, however, no additive effect of ENP and MON was observed for mitigating CH4 production.

Effect of a Phytogenic Feed Additive in Preventing Calves' Diarrhea

The aims of the present study were to evaluate the preventive and the therapeutic effect of Stodi® as phytogenic feed additive rich in phenolic substances on the calf diarrhea, during the first 24 days of life. A total of 40 calves were included and randomly divided into Group C (control group) and Group T (treated group) with placebo or treatment administration started from the third day of life (T0). Calves belonged to group C received 2 L of warm water, while the calves assigned to group T received 2L of warm water plus 30 g of Stodi®. Solutions administration was maintained until day 21 (T21) that was the end of the experimental period. Calves were weighed at T0 and T21 to assess the average daily gain (ADG). Physical examination and fecal score evaluation were performed daily. The duration of a diarrheic episode, the age of the first diarrhea outbreak (TDE) and the frequency of diarrheic episodes were recorded. Complete blood count, methemoglobin and liver enzymes were evaluated at T0 and at T21 in all the calves by spectrophotometer and clinical chemistry analysis, respectively. Data were analyzed using a mixed model. A Chi-square and a Mann-Whitney test were also performed. No difference was found for ADG between the groups. The difference of mean age at TDE was not statistically significant between C and T group. The number of calves with diarrhea in the C group tended to be higher than that of T group (p = 0.13). Calves in group C spent more days with clinical sign of diarrhea compared to group T (p = 0.016). Complete blood count, methemoglobin and liver enzymes were within the reference ranges. The feed additive Stodi® seemed to be effective in shortening neonatal diarrhea episodes in calves thanks to the administration of 30 g per day of product. The fixed dosage of Stodi® used in our study did not show a preventive effect to reduce the incidence of calf diarrhea.

Feeding Calcium-Ammonium Nitrate to Lactating Dairy Goats: Milk Quality and Ruminal Fermentation Responses

Simple Summary

Calcium-ammonium nitrate (CAN) has been extensively used as a potential methane inhibitor for ruminants; however, there is still a need for studies focused on investigating its effects on the fatty acid profile and antioxidant capacity of milk, especially from dairy goats. Therefore, we evaluated the effects of CAN on nutrient digestibility, ruminal fermentation, and milk quality of lactating Saanen goats. Treatments consisted of a control diet (without CAN), 10 g of CAN per kg of dry matter, and 20 g of CAN per kg of dry matter. Supplemental CAN did not affect feed intake, digestibility of nutrients, and most ruminal fermentation parameters. Yields and composition of milk were not affected, and minor treatment effects were observed on the milk fatty acid profile. Milk antioxidant capacity was altered by increased conjugated dienes and reduced thiobarbituric acid reactive substances, along with greater concentrations of nitrate and nitrite residues in milk. Calcium-ammonium nitrate can be fed to lactating dairy goats up to 20 g per kg of dry matter without negative effects on nutrient digestibility and milk composition; however, it increased the concentration of conjugated dienes in milk, which may induce its faster lipid oxidation.

Abstract

We aimed to investigate the effects of calcium-ammonium nitrate (CAN) fed to lactating dairy goats on dry matter (DM) intake, digestibility of nutrients, milk properties (composition, antioxidant capacity, fatty acid profile, and nitrate residues), and ruminal fermentation parameters. Twelve lactating Saanen goats averaging 98.5 ± 13.1 days in milk, 53.5 ± 3.3 kg of body weight, and 2.53 ± 0.34 kg of milk/day were randomly assigned in four 3 × 3 Latin squares to receive the following diets: a control group (without CAN) with 7.3 g/kg DM of urea (URE), 10 g/kg DM of CAN (CAN10), and 20 g/kg DM of CAN (CAN20). Each period lasted 21 days, with 14 days for diet adaptation and seven days for data and sample collection. The DM intake, digestibility of nutrients, yields of milk, 3.5% fat-corrected milk, and energy-corrected milk were not affected by treatments. Similarly, there were no treatment effects on the yields and concentrations of milk fat, true protein, and lactose, along with minor effects on milk fatty acid profile. Total antioxidant capacity in milk was unaffected by treatments; however, concentration of conjugated dienes increased, while thiobarbituric acid reactive substances in milk decreased linearly. Nitrate and nitrite residues in milk were elevated by treatments, while the total of volatile fatty acids and ammonia-N concentration in the rumen were unaffected. Collectively, feeding CAN (up to 20 g/kg of DM) to lactating dairy goats did not affect feed intake, nutrient digestibility, and milk composition; however, it may increase milk lipid oxidation, as evidenced by increased conjugated diene concentration.

Board Invited Review: Enteric methane mitigation interventions

Mitigation of enteric methane (CH₄) presents a feasible approach to curbing agriculture’s contribution to climate change. One intervention for reduction is dietary reformulation, which manipulates the composition of feedstuffs in ruminant diets to redirect fermentation processes toward low CH₄ emissions. Examples include reducing the relative proportion of forages to concentrates, determining the rate of digestibility and passage rate from the rumen, and dietary lipid inclusion. Feed additives present another intervention for CH₄ abatement and are classified based on their mode of action. Through inhibition of key enzymes, 3-nitrooxypropanol (3-NOP) and halogenated compounds directly target the methanogenesis pathway. Rumen environment modifiers, including nitrates, essential oils, and tannins, act on the conditions that affect methanogens and remove the accessibility of fermentation products needed for CH₄ formation. Low CH₄-emitting animals can also be directly or indirectly selected through breeding interventions, and genome-wide association studies are expected to provide efficient selection decisions. Overall, dietary reformulation and feed additive inclusion provide immediate and reversible effects, while selective breeding produces lasting, cumulative CH₄ emission reductions.

Strategies to Mitigate Enteric Methane Emissions from Ruminant Animals

Human activities account for approximately two-thirds of global methane emissions, wherein the livestock sector is the single massive methane emitter. Methane is a potent greenhouse gas of over 21 times the warming effect of carbon dioxide. In the rumen, methanogens produce methane as a by-product of anaerobic fermentation. Methane released from ruminants is considered as a loss of feed energy that could otherwise be used for productivity. Economic progress and growing population will inflate meat and milk product demands, causing elevated methane emissions from this sector. In this review, diverse approaches from feed manipulation to the supplementation of organic and inorganic feed additives and direct-fed microbial in mitigating enteric methane emissions from ruminant livestock are summarized. These approaches directly or indirectly alter the rumen microbial structure thereby reducing rumen methanogenesis. Though many inorganic feed additives have remarkably reduced methane emissions from ruminants, their usage as feed additives remains unappealing because of health and safety concerns. Hence, feed additives sourced from biological materials such as direct-fed microbials have emerged as a promising technique in mitigating enteric methane emissions.

Nitrate Water Contamination from Industrial Activities and Complete Denitrification as a Remediation Option

Freshwater is a scarce resource that continues to be at high risk of pollution from anthropogenic activities, requiring remediation in such cases for its continuous use. The agricultural and mining industries extensively use water and nitrogen (N)-dependent products, mainly in fertilizers and explosives, respectively, with their excess accumulating in different water bodies. Although removal of NO3 from water and soil through the application of chemical, physical, and biological methods has been studied globally, these methods seldom yield N2 gas as a desired byproduct for nitrogen cycling. These methods predominantly cause secondary contamination with deposits of chemical waste such as slurry brine, nitrite (NO2), ammonia (NH3), and nitrous oxide (N2O), which are also harmful and fastidious to remove. This review focuses on complete denitrification facilitated by bacteria as a remedial option aimed at producing nitrogen gas as a terminal byproduct. Synergistic interaction of different nitrogen metabolisms from different bacteria is highlighted, with detailed attention to the optimization of their enzymatic activities. A biotechnological approach to mitigating industrial NO3 contamination using indigenous bacteria from wastewater is proposed, holding the prospect of optimizing to the point of complete denitrification. The approach was reviewed and found to be durable, sustainable, cost effective, and environmentally friendly, as opposed to current chemical and physical water remediation technologies.

Sodium nitrate has no detrimental effect on milk fatty acid profile and rumen bacterial population in water buffaloes

This study evaluated the influence of dietary sodium nitrate on ruminal fermentation profiles, milk production and composition, microbial populations and diversity in water buffaloes. Twenty-four female water buffaloes were randomly divided into four groups and fed with 0, 0.11, 0.22, 044 g sodium nitrate per kg body weight diets, respectively. Results showed that the concentration of acetate, propionate, butyrate and total VFA in all sodium nitrate–adapted water buffaloes were greater than the control group (P  < 0.05). Although the milk fatty acids value at 0.11 g sodium nitrate/kg/d were slightly lower than other treatments, no significant differences were observed among different treatments (P  > 0.05). Compared to the control group, the archaea richness (ace and chao1) and diversity (Shannon index) indices were increased by nitrate supplementation (P  < 0.05). Compared with the control group, sodium nitrate did not affect bacterial abundance at the phylum and genus level, but the relative abundance of the methanogen genera was greatly changed. There was a tendency for Methanobrevibacter to decrease in the sodium nitrate group (P  = 0.091). Comparisons of archaea communities by PCoA analysis showed significant separation between the control group and nitrate treatments (P  = 0.025). It was concluded that added 0.11–0.44 g sodium nitrate/kg of body weight increased the rumen VFA production and archaeal diversity of water buffaloes but had no detrimental effect on milk yield or composition, fatty acids profile, rumen methanogen or Butyrivibrio group population related to biohydrogenation.

Fungal and ciliate protozoa are the main rumen microbes associated with methane emissions in dairy cattle

BACKGROUND

Mitigating the effects of global warming has become the main challenge for humanity in recent decades. Livestock farming contributes to greenhouse gas emissions, with an important output of methane from enteric fermentation processes, mostly in ruminants. Because ruminal microbiota is directly involved in digestive fermentation processes and methane biosynthesis, understanding the ecological relationships between rumen microorganisms and their active metabolic pathways is essential for reducing emissions. This study analysed whole rumen metagenome using long reads and considering its compositional nature in order to disentangle the role of rumen microbes in methane emissions.

RESULTS

The β-diversity analyses suggested a subtle association between methane production and overall microbiota composition (0.01 < R2 < 0.02). Differential abundance analysis identified 36 genera and 279 KEGGs as significantly associated with methane production (Padj < 0.05). Those genera associated with high methane production were Eukaryota from Alveolata and Fungi clades, while Bacteria were associated with low methane emissions. The genus-level association network showed 2 clusters grouping Eukaryota and Bacteria, respectively. Regarding microbial gene functions, 41 KEGGs were found to be differentially abundant between low- and high-emission animals and were mainly involved in metabolic pathways. No KEGGs included in the methane metabolism pathway (ko00680) were detected as associated with high methane emissions. The KEGG network showed 3 clusters grouping KEGGs associated with high emissions, low emissions, and not differentially abundant in either. A deeper analysis of the differentially abundant KEGGs revealed that genes related with anaerobic respiration through nitrate degradation were more abundant in low-emission animals.

CONCLUSIONS

Methane emissions are largely associated with the relative abundance of ciliates and fungi. The role of nitrate electron acceptors can be particularly important because this respiration mechanism directly competes with methanogenesis. Whole metagenome sequencing is necessary to jointly consider the relative abundance of Bacteria, Archaea, and Eukaryota in the statistical analyses. Nutritional and genetic strategies to reduce CH4 emissions should focus on reducing the relative abundance of Alveolata and Fungi in the rumen. This experiment has generated the largest ONT ruminal metagenomic dataset currently available.

Effects of calcium ammonium nitrate fed to dairy cows on nutrient intake and digestibility, milk quality, microbial protein synthesis, and ruminal fermentation parameters

We evaluated the effects of supplemental calcium ammonium nitrate (CAN) fed to dairy cows on dry matter (DM) intake, nutrient digestibility, milk quality, microbial protein synthesis, and ruminal fermentation. Six multiparous Holstein cows at 106 ± 14.8 d in milk, with 551 ± 21.8 kg of body weight were used in a replicated 3 × 3 Latin square design. Experimental period lasted 21 d, with 14 d for an adaptation phase and 7 d for sampling and data collection. Cows were randomly assigned to receive the following treatments: URE, 12 g of urea/kg of DM as a control group; CAN15, 15 g of CAN/kg of DM; and CAN30, 30 g of CAN/kg of DM. Supplemental CAN reduced DM intake (URE 19.0 vs. CAN15 18.9 vs. CAN30 16.5 kg/d). No treatment effects were observed for apparent digestibility of DM, organic matter, crude protein, ether extract, and neutral detergent fiber; however, CAN supplementation linearly increased nonfiber carbohydrate digestibility. Milk yield was not affected by treatments (average = 23.1 kg/d), whereas energy-corrected milk (ECM) and 3.5% fat-corrected milk (FCM) decreased as the levels of CAN increased. Nitrate residue in milk increased linearly (URE 0.30 vs. CAN15 0.33 vs. CAN30 0.38 mg/L); however, treatments did not affect nitrite concentration (average: 0.042 mg/L). Milk fat concentration was decreased (URE 3.39 vs. CAN15 3.35 vs. CAN30 2.94%), and the proportion of saturated fatty acids was suppressed by CAN supplementation. No treatment effects were observed on the reducing power and thiobarbituric acid reactive substances of milk, whereas conjugated dienes increased linearly (URE 47.6 vs. CAN15 52.7 vs. CAN30 63.4 mmol/g of fat) with CAN supplementation. Treatments had no effect on microbial protein synthesis; however, molar proportion of ruminal acetate and acetate-to-propionate ratio increased with CAN supplementation. Based on the results observed, supplementing CAN at 30 g/kg of DM should not be recommended as an optimal dose because it lowered DM intake along with ECM and 3.5% FCM, although no major changes were observed on milk quality and ruminal fermentation.

Nitrates in the environment: A critical review of their distribution, sensing techniques, ecological effects and remediation

Nitrate pollution is eminent in almost all the developing nations as a result of increased natural activities apart from anthropogenic pollution. The release of nitrates in more than critical quantities into the water bodies causes accretion impacts on living creatures, environmental receptors, and human vigour by accumulation through the food chain. Nitrates have recently acquired researchers' huge attention and extend their roots in environmental contamination of surface and groundwater systems. The presence of nitrate in high concentrations in surface and groundwater triggers several health problems, for instance, methemoglobinemia, diabetes, eruption of infectious disorders, harmfully influence aquatic organisms. Sensing nitrate is an alternate option for monitoring the distribution of nitrate in different water bodies. Here we review electrochemical, spectroscopic, and electrical modes of nitrate sensing. It is concluded that, among the various sensors discussed in this review, FET sensors are the most desirable choice. Their sensitivity, ease of use and scope for miniaturisation are exceptional. Advanced functional materials need to be designed to satiate the growing need for environmental monitoring. Different sources of nitrate contamination in ground and surface water can be estimated using different techniques such as nitrate isotopic composition, co contaminants, water tracers, and other specialized techniques. This review intends to explore the research work on remediation of nitrate from wastewater and soil using different processes such as reverse osmosis, chemical denitrification, biological denitrification, ion exchange, electrodialysis, and adsorption. Denitrification proves as a promising alternative over previously reported techniques in terms of their nitrate removal because of its high cost-effectiveness.

Is it time to rethink our one-size-fits-all approach to nitrate toxicity thresholds in forages?

Annual forages provide a valuable grazing resource for cattle producers; however, annuals are prone to accumulating nitrate and have the potential to cause nitrate toxicity. Although these forages pose a risk of containing high nitrate concentrations, they can be a high-quality feed source. Understanding the factors that affect the potential for toxicity when using these forages is important to help nutritionists and producers make management decisions. This review describes the previous research, current guidelines for nitrate toxicity, and the potential for improvement in our current recommendations. Current extension toxicity guidelines appear to be founded primarily on drenching based studies and overestimate the nitrate toxicity potential of forages. Recommendations need to account for multiple factors that affect the threshold for toxicity. There is evidence that fresh forages have a lower risk of toxicity because of slower release of nitrate into the rumen and a slower rate of dry matter intake. Increased dietary energy and sulfur content reduce the potential for toxicity. Microbial adaptation can reduce the risk and allow use of potentially toxic forages. These factors should influence feeding recommendations. However, there is currently not enough data available to establish new guidelines that account for these main factors. Thus, there is a need for renewed research in this area. The limited number of studies grazing elevated nitrate forages seems to suggest that there is less risk in grazing situations, especially if animals graze selectively. There is a need to develop guidelines for nitrate toxicity and management recommendations when grazing. To accomplish this, there is a need for more studies to evaluate risk of toxicity in grazing situations. These grazing studies need to evaluate the effects of nitrate concentration, forage quality, and grazing management on the potential for nitrate toxicity. While the conservative guidelines that are currently in use reduce risk of nitrate toxicity, they may also cause a significant increase in feed costs for producers.

Meta-analysis quantifying the potential of dietary additives and rumen modifiers for methane mitigation in ruminant production systems

Increasingly countries are seeking to reduce emission of greenhouse gases from the agricultural industries, and livestock production in particular, as part of their climate change management. While many reviews update progress in mitigation research, a quantitative assessment of the efficacy and performance-consequences of nutritional strategies to mitigate enteric methane (CH₄) emissions from ruminants has been lacking. A meta-analysis was conducted based on 108 refereed papers from recent animal studies (2000–2020) to report effects on CH₄ production, CH₄ yield and CH₄ emission intensity from 8 dietary interventions. The interventions (oils, microalgae, nitrate, ionophores, protozoal control, phytochemicals, essential oils and 3-nitrooxypropanol). Of these, macroalgae and 3-nitrooxypropanol showed greatest efficacy in reducing CH₄ yield (g CH₄/kg of dry matter intake) at the doses trialled. The confidence intervals derived for the mitigation efficacies could be applied to estimate the potential to reduce national livestock emissions through the implementation of these dietary interventions.

Sustainability of the Dairy Industry: Emissions and Mitigation Opportunities

Dairy cattle provide a major benefit to the world through upcycling human inedible feedstuffs into milk and associated dairy products. However, as beneficial as this process has become, it is not without potential negatives. Dairy cattle are a source of greenhouse gases through enteric and waste fermentation as well as excreting nitrogen emissions through their feces and urine. However, these negative impacts vary widely due to how and what these animals are fed. In addition, there are many promising opportunities for further reducing emissions through feed and waste additives. The present review aims to further expand on where the industry is today and the potential avenues for improvement. This area of research is still not complete and additional information is required to further improve our dairy systems impact on sustainable animal products.

Review of potential risks associated with supplemental dietary exposure to nitrate-containing compounds in swine-a paradox in light of emerging benefits

Calcium nitrate has been reported to benefit reproductive outcomes in sows and their offspring when administered via the feed (15 to 19 mg/kg-body weight [bw]/day) during the periparturient period. Traditionally, dietary nitrate had been considered a methemoglobinemia (MetHb) risk in swine. Similar hazard concerns have existed in humans, but a recent benefit/risk analysis established that nitrate levels associated with well-recognized health benefits outweigh potential risks. A similar benefit/risk perspective in swine was lacking and challenged by sparse published hazard data, often referenced within larger reviews related to all livestock. The objective of this review was to better characterize the potential for adverse health and performance effects reported in the literature for swine consuming nitrate and to provide metrics for evaluating the reliability of the studies reviewed. Supplemental exposure via feed or drinking water was considered for any life stage, dose, and exposure duration. More than 30 relevant studies, including case reports and reviews, examined calcium, potassium, sodium, or unspecified nitrate salts at doses up to 1,800 mg nitrate/kg-bw/day for exposures ranging from 1 to 105 d. The studies primarily evaluated weight gain, blood methemoglobin levels, or vitamin A homeostasis in sows or growing swine. An extensive review of the literature showed reports of adverse effects at low nitrate doses to be of low reliability. Conversely, reliable studies corroborate nitrate intake from feed or drinking water at levels equal to or greater than the European Food Safety Authority's no-observed-adverse-effect level (NOAEL) for swine of 410 mg nitrate/kg-bw/day, with no MetHb or other adverse effects on reproduction, growth, or vitamin A levels. Using a weight-of-evidence evaluation, we have moderate-to-high confidence that the NOAEL for nitrate supplementation in swine is likely between 600 and 800 mg/kg-bw/day. These levels are several-fold higher than dietary nitrate concentrations (19 mg/kg-bw/day) that are known to benefit birth outcomes in sows. This review elucidates the quality and reliability of the information sources historically used to characterize nitrate in swine feed as a contaminant of concern. Results from this evaluation can assist risk managers (e.g., regulatory officials and veterinarians) in consideration of proposed benefits as well as reassuring swine producers that low-level nitrate supplementation is not anticipated to be a concern.

A novel identified Pseudomonas aeruginosa, which exhibited nitrate- and nitrite-dependent methane oxidation abilities, could alleviate the disadvantages caused by nitrate supplementation in rumen fluid fermentation

After the occurrence of nitrate-dependent anaerobic methane oxidation (AMO) in rumen fluid culture was proved, the organisms that perform the denitrifying anaerobic methane oxidizing (DAMO) process in the rumen of dairy goat were investigated by establishing two enrichment culture systems, which were supplied with methane as the sole carbon source and NaNO3 or NaNO2 as the electron acceptor. Several Operational Taxonomic Units (OTU) belonging to Proteobacteria became dominant in the two enrichment systems. The identified Pseudomonas aeruginosa, which was isolated from the NaNO2 enrichment system, could individually perform a whole denitrifying anaerobic methane oxidizing process. Further in vitro rumen fermentation showed that supplementation with the isolated P. aeruginosa could reduce methane emissions, alleviate the nitrite accumulation and prevent the decrease in propionic acid product caused by nitrate supplementation.

Nitrate supplementation at two forage levels in dairy cows feeding: milk production and composition, fatty acid profiles, blood metabolites, ruminal fermentation, and hydrogen sink

Nitrate may reduce the ruminal methane emission by competing methanogenesis to achieve more hydrogen. For this purpose, twenty Holstein lactating cows were examined using a 2×2 factorial design in 4 groups for 60 days with two forage levels (40% and 60%) and supplemental nitrate 0% (F40 and F60) and 3.5% (F40N and F60N) of diet dry matter (DM). Then, the effect of nitrate and forage levels on cow performance, ruminal fermentation, methane emission, and metabolic hydrogen sink were evaluated. The nitrate supplementation did not significantly affect milk yield and ECM/DMI while, milk urea nitrogen was increased. Lowest quantity of milk vitamins (A and E) was observed in nitrate groups. The nitrate supplementation increased c9-C18:1, unsaturated fatty acids, and n-6/n-3 contents of the milk. Blood parameters were affected by nitrate supplementation. Blood met-Hb concentration was increased, while blood glucose was decreased in nitrate groups. High forage and nitrate fed animals (F60N) had higher ruminal acetate and lower propionate concentration, and higher acetate+butyrate to propionate ratio than other groups. Nitrite and NH3-N concentrations were higher in the rumen of nitrate fed animals. Nitrate supplementation inhibited gas volume and methane emission without affecting volatile fatty acids at 12 and 24 h of incubation. The H2 balance, H2 production and consumption, and recovery percentage were significantly lower in F60N group. In conclusion, nitrate supplementation can be employed as an alternative strategy for improving ruminal fermentation, milk quality and methane inhibition.

Methane Emissions from Ruminants in Australia: Mitigation Potential and Applicability of Mitigation Strategies

Anthropomorphic greenhouse gases are raising the temperature of the earth and threatening ecosystems. Since 1950 atmospheric carbon dioxide has increased 28%, while methane has increased 70%. Methane, over the first 20 years after release, has 80-times more warming potential as a greenhouse gas than carbon dioxide. Enteric methane from microbial fermentation of plant material by ruminants contributes 30% of methane released into the atmosphere, which is more than any other single source. Numerous strategies were reviewed to quantify their methane mitigation potential, their impact on animal productivity and their likelihood of adoption. The supplements, 3-nitrooxypropanol and the seaweed, Asparagopsis, reduced methane emissions by 40+% and 90%, respectively, with increases in animal productivity and small effects on animal health or product quality. Manipulation of the rumen microbial population can potentially provide intergenerational reduction in methane emissions, if treated animals remain isolated. Genetic selection, vaccination, grape marc, nitrate or biochar reduced methane emissions by 10% or less. Best management practices and cattle browsing legumes, Desmanthus or Leucaena species, result in small levels of methane mitigation and improved animal productivity. Feeding large amounts daily of ground wheat reduced methane emissions by around 35% in dairy cows but was not sustained over time.

Changes in hematological, biochemical, and blood gases parameters in response to progressive inclusion of nitrate in the diet of Holstein calves

Background and Aim:

Nitrate (NO₃^-) reduces enteric methane emissions and could be a source of non-protein nitrogen in ruminant feeds. Nonetheless, it has a potential toxic effect that could compromise animal health and production. The purpose of this study was to determine the effects of progressive inclusion of NO₃^- in the diet on the hematological, biochemical, and blood gases parameters, in turn, the effects on feed intake and live weight gain (LWG) in Holstein calves.

Materials and Methods:

Eighteen Holstein heifers and steers (nine animals/treatment) were maintained in individual pens for 45 days. Animals were randomly allocated to either a control or nitrate diet (ND) (containing 15 g of NO₃^-/kg of dry matter [DM]). The biochemical parameters and blood gases were analyzed only in the NO₃^- group on days: -1, 1, 7, 13, 19, and 25 corresponding to 0, 20, 40, 60, 80, and 100% of the total inclusion of NO₃^- in the diet, respectively. In addition, DM intake (DMI) and LWG were evaluated among dietary treatments.

Results:

Feeding the ND did not influence DMI or LWG (p>0.05). Methemoglobin (MetHb) and deoxyhemoglobin increased according to the NO₃^- concentrations in the diet (p<0.05), while an opposite effect was observed for oxyhemoglobin and carboxyhemoglobin (p<0.05). Hematocrit levels decreased (p<0.05), while albumin, alanine aminotransferase, and gamma-glutamyl transpeptidase concentrations were not modified (p>0.05). However, glucose, urea, aspartate aminotransferase (AST), and retinol concentrations increased (p<0.05) according to the NO₃^- concentrations in the diet.

Conclusion:

This study confirmed that the progressive inclusion of 123 g of NO₃^-/animal/day in the diet could be safe without affecting DMI and LWG of Holstein calves. In turn, a dose-response effect of the MetHb, glucose, urea, AST, and retinol was observed, but these values did not exceed reference values. These results highlighted the importance of using a scheme of progressive inclusion of NO₃^- in the diet of calves to reduce the risks of NO₃^- toxicity.

The effect of molasses nitrate lick blocks on supplement intake, bodyweight, condition score, blood methaemoglobin concentration and herd scale methane emissions in Bos indicus cows grazing poor quality forage

Context The Australian government has approved a greenhouse gas (GHG) offset method that requires cattle to consume nitrate in the form of a lick block. Field studies demonstrating the effectiveness of this methodology have not been previously reported. Aims This experiment was conducted to determine the effects on productivity and health when nitrate lick blocks were provided as a supplement to grazing beef cattle. We hypothesised that beef cattle given access to nitrate lick blocks would have similar productivity compared with cattle offered urea lick blocks. Methods Bos indicus breeding cows (n = 76) grazed a 467-ha paddock near Charters Towers, Queensland, between May and November 2014. A two-way remote automatic drafting system enabled allocation of cattle to different treatments while grazing in a common paddock. Treatments were 30% urea lick blocks (30U), or molasses nitrate lick blocks (MNB). At monthly intervals liveweight (LW), body condition score (BCS), and blood methaemoglobin concentration were recorded. Estimates of individual supplement intake were made on three separate occasions using a lithium marker technique. Results Mean daily supplement intake (±s.e.m.) of 30U (122 ± 13 g) was greater (P &lt; 0.001) than MNB (67 ± 8 g). Lesser MNB intake was associated with greater variability for individual supplement intake, a greater proportion of non-consumers of supplement during July (P &lt; 0.05) and reduced voluntary supplement intake until October (P &lt; 0.001). Increasing MNB consumption during October and November was accompanied by elevated blood methaemoglobin concentration (P &lt; 0.001). It was estimated that cattle offered MNB had insufficient supplementary nitrogen intake throughout the study to resolve rumen degradable nitrogen deficiency from grazed forage. Consequently, cattle provided access to MNB demonstrated conceptus free liveweight loss and lesser BCS compared with cattle treated with 30U (P &lt; 0.001). Conclusion Nitrate lick blocks were ineffective as a dual-purpose non-protein nitrogen supplement and methane mitigant for beef cattle grazing poor quality forage. Further field experiments are required to determine if there may be situations where this GHG offset methodology is efficacious. Implications Caution is advised in implementing GHG mitigation methods that involve the use of nitrate lick blocks.

Risk assessment of nitrate and nitrite in feed

The European Commission asked EFSA for a scientific opinion on the risks to animal health related to nitrite and nitrate in feed. For nitrate ion, the EFSA Panel on Contaminants in the Food Chain (CONTAM Panel) identified a BMDL 10 of 64 mg nitrate/kg body weight (bw) per day for adult cattle, based on methaemoglobin (MetHb) levels in animal's blood that would not induce clinical signs of hypoxia. The BMDL 10 is applicable to all bovines, except for pregnant cows in which reproductive effects were not clearly associated with MetHb formation. Since the data available suggested that ovines and caprines are not more sensitive than bovines, the BMDL 10 could also be applied to these species. Highest mean exposure estimates of 53 and 60 mg nitrate/kg bw per day in grass silage-based diets for beef cattle and fattening goats, respectively, may raise a health concern for ruminants when compared with the BMDL 10 of 64 mg nitrate/kg bw per day. The concern may be higher because other forages might contain higher levels of nitrate. Highest mean exposure estimates of 2.0 mg nitrate/kg bw per day in pigs' feeds indicate a low risk for adverse health effects, when compared with an identified no observed adverse effect level (NOAEL) of 410 mg nitrate/kg bw per day, although the levels of exposure might be underestimated due to the absence of data on certain key ingredients in the diets of this species. Due to the limitations of the data available, the CONTAM Panel could not characterise the health risk in species other than ruminants and pigs from nitrate and in all livestock and companion animals from nitrite. Based on a limited data set, both the transfer of nitrate and nitrite from feed to food products of animal origin and the nitrate- and nitrite-mediated formation of N-nitrosamines and their transfer into these products are likely to be negligible.

Antimethanogenic effects of nitrate supplementation in cattle: A meta-analysis

Supplementing a diet with nitrate is regarded as an effective and promising methane (CH₄) mitigation strategy by competing with methanogens for available hydrogen through its reduction of ammonia in the rumen. Studies have shown major reductions in CH₄ emissions with nitrate supplementation, but with large variation in response. The objective of this study was to quantitatively investigate the effect of dietary nitrate on enteric CH₄ production and yield and evaluate the variables with high potential to explain the heterogeneity of between-study variability using meta-analytical models. A data set containing 56 treatments from 24 studies was developed to conduct a meta-analysis. Dry matter (DM) intake, nitrate dose (g/kg of DM), animal body weight, roughage proportion of diet, dietary crude protein and neutral detergent fiber content, CH₄ measurement technique, and type of cattle (beef or dairy) were considered as explanatory variables. Average DM intake and CH₄ production for dairy cows (16.2 ± 2.93 kg/d; 311 ± 58.8 g/d) were much higher than for beef cattle (8.1 ± 1.57 kg/d; 146 ± 50.9 g/d). Therefore, a relative mean difference was calculated and used to conduct random-effect and mixed-effect model analysis to eliminate the large variations between types of animal due to intake. The final mixed-effect model for CH₄ production (g of CH₄/d) had 3 explanatory variables and included nitrate dose, type of cattle, and DM intake. The final mixed-effect model for CH₄ yield (g of CH₄/kg of DM intake) had 2 explanatory variables and included nitrate dose and type of cattle. Nitrate effect sizes on CH₄ production (dairy: -20.4 ± 1.89%; beef: -10.1 ± 1.52%) and yield (dairy: -15.5 ± 1.15%; beef: -8.95 ± 1.764%) were significantly different between the 2 types of cattle. When data from slow-release nitrate sources were removed from the analysis, there was no significant difference in type of cattle anymore for CH₄ production and yield. Nitrate dose enhanced the mitigating effect of nitrate on CH₄ production and yield by 0.911 ± 0.1407% and 0.728 ± 0.2034%, respectively, for every 1 g/kg of DM increase from its mean dietary inclusion (16.7 g/kg of DM). An increase of 1 kg of DM/d in DM intake from its mean dietary intake (11.1 kg of DM/d) decreased the effect of nitrate on CH₄ production by 0.691 ± 0.2944%. Overall, this meta-analysis demonstrated that nitrate supplementation reduces CH₄ production and yield in a dose-dependent manner, and that elevated DM intake decreases the effect of nitrate supplementation on CH₄ production. Furthermore, the stronger antimethanogenic effect on CH₄ production and yield in dairy cows than in beef steers could be related to use of slow-release nitrate in beef cattle.

Net reductions in greenhouse gas emissions from feed additive use in California dairy cattle

The livestock industry is one of the main contributors to greenhouse gas emissions and there is an increasing demand for the industry to reduce its carbon footprint. Several studies have shown that feed additives 3-nitroxypropanol and nitrate to be effective in reducing enteric methane emissions. The objective of this study was to estimate the net mitigating effect of using 3-nitroxypropanol and nitrate on total greenhouse gas emissions in California dairy industry. A life cycle assessment approach was used to conduct a cradle-to-farm gate environmental impact analysis based on dairy production system in California. Emissions associated with crop production, feed additive production, enteric methane, farm management, and manure storage were calculated and expressed as kg CO2 equivalents (CO2e) per kg of energy corrected milk. The total greenhouse gas emissions from baseline, 3-nitroxypropanol and nitrate offered during lactation were 1.12, 0.993, and 1.08 kg CO2e/kg energy corrected milk, respectively. The average net reduction rates for 3-nitroxypropanol and nitrate were 11.7% and 3.95%, respectively. In both cases, using the feed additives on the whole herd slightly improved overall carbon footprint reduction compared to limiting its use during lactation phase. Although both 3-nitroxypropanol and nitrate had effects on decreasing the total greenhouse gas emission, the former was much more effective with no known safety issues in reducing the carbon footprint of dairy production in California.

Review: Strategies for enteric methane mitigation in cattle fed tropical forages

Methane (CH4) is a greenhouse gas (GHG) produced and released by eructation to the atmosphere in large volumes by ruminants. Enteric CH4 contributes significantly to global GHG emissions arising from animal agriculture. It has been contended that tropical grasses produce higher emissions of enteric CH4 than temperate grasses, when they are fed to ruminants. A number of experiments have been performed in respiration chambers and head-boxes to assess the enteric CH4 mitigation potential of foliage and pods of tropical plants, as well as nitrates (NO3-) and vegetable oils in practical rations for cattle. On the basis of individual determinations of enteric CH4 carried out in respiration chambers, the average CH4 yield for cattle fed low-quality tropical grasses (>70% ration DM) was 17.0 g CH4/kg DM intake. Results showed that when foliage and ground pods of tropical trees and shrubs were incorporated in cattle rations, methane yield (g CH4/kg DM intake) was decreased by 10% to 25%, depending on plant species and level of intake of the ration. Incorporation of nitrates and vegetable oils in the ration decreased enteric CH4 yield by ∼6% to ∼20%, respectively. Condensed tannins, saponins and starch contained in foliages, pods and seeds of tropical trees and shrubs, as well as nitrates and vegetable oils, can be fed to cattle to mitigate enteric CH4 emissions under smallholder conditions. Strategies for enteric CH4 mitigation in cattle grazing low-quality tropical forages can effectively increase productivity while decreasing enteric CH4 emissions in absolute terms and per unit of product (e.g. meat, milk), thus reducing the contribution of ruminants to GHG emissions and therefore to climate change.

Inhibition of methanogenesis by nitrate, with or without defaunation, in continuous culture

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.

Review: Fifty years of research on rumen methanogenesis: lessons learned and future challenges for mitigation

Meat and milk from ruminants provide an important source of protein and other nutrients for human consumption. Although ruminants have a unique advantage of being able to consume forages and graze lands not suitable for arable cropping, 2% to 12% of the gross energy consumed is converted to enteric CH4 during ruminal digestion, which contributes approximately 6% of global anthropogenic greenhouse gas emissions. Thus, ruminant producers need to find cost-effective ways to reduce emissions while meeting consumer demand for food. This paper provides a critical review of the substantial amount of ruminant CH4-related research published in past decades, highlighting hydrogen flow in the rumen, the microbiome associated with methanogenesis, current and future prospects for CH4 mitigation and insights into future challenges for science, governments, farmers and associated industries. Methane emission intensity, measured as emissions per unit of meat and milk, has continuously declined over the past decades due to improvements in production efficiency and animal performance, and this trend is expected to continue. However, continued decline in emission intensity will likely be insufficient to offset the rising emissions from increasing demand for animal protein. Thus, decreases in both emission intensity (g CH4/animal product) and absolute emissions (g CH4/day) are needed if the ruminant industries continue to grow. Providing producers with cost-effective options for decreasing CH4 emissions is therefore imperative, yet few cost-effective approaches are currently available. Future abatement may be achieved through animal genetics, vaccine development, early life programming, diet formulation, use of alternative hydrogen sinks, chemical inhibitors and fermentation modifiers. Individually, these strategies are expected to have moderate effects (<20% decrease), with the exception of the experimental inhibitor 3-nitrooxypropanol for which decreases in CH4 have consistently been greater (20% to 40% decrease). Therefore, it will be necessary to combine strategies to attain the sizable reduction in CH4 needed, but further research is required to determine whether combining anti-methanogenic strategies will have consistent additive effects. It is also not clear whether a decrease in CH4 production leads to consistent improved animal performance, information that will be necessary for adoption by producers. Major constraints for decreasing global enteric CH4 emissions from ruminants are continued expansion of the industry, the cost of mitigation, the difficulty of applying mitigation strategies to grazing ruminants, the inconsistent effects on animal performance and the paucity of information on animal health, reproduction, product quality, cost-benefit, safety and consumer acceptance.

Dietary nitrate and presence of protozoa increase nitrate and nitrite reduction in the rumen of sheep

Nitrate ( NO 3 - ) supplementation is an effective methane (CH₄ ) mitigation strategy for ruminants but may produce nitrite ( NO 2 - ) toxicity. It has been reported that rumen protozoa have greater ability for NO 3 - and NO 2 - reduction than bacteria. It was hypothesised that the absence of ruminal protozoa in sheep may lead to higher NO 2 - accumulation in the rumen and a higher blood methaemoglobin (MetHb) concentration. An in vivo experiment was conducted with defaunated (DEF) and faunated (FAU) sheep supplemented with 1.8% NO 3 - in DM. The effects of rumen protozoa on concentrations of plasma and ruminal NO 3 - and NO 2 - , blood MetHb, ruminal volatile fatty acid (VFA) and ruminal ammonia (NH₃ ) were investigated. Subsequently, two in vitro experiments were conducted to determine the contribution of protozoa to NO 3 - and NO 2 - reduction rates in DEF and FAU whole rumen digesta (WRD) and its liquid (LIQ) and solid (SOL) fractions, incubated alone (CON), with the addition of NO 3 - or with the addition of NO 2 - . The results from the in vivo experiment showed no differences in total VFA concentrations, although ruminal NH₃ was greater (p < .01) in FAU sheep. Ruminal NO 3 - , NO 2 - and plasma NO 2 - concentrations tended to increase (p < .10) 1.5 hr after feeding in FAU relative to DEF sheep. In vitro results showed that NO 3 - reduction to NH₃ was stimulated (p < .01) by incoming NO 3 - in both DEF and FAU relative to CON digesta. However, adding NO 3 - increased (p < .05) the rate of NO 2 - accumulation in the SOL fraction of DEF relative to both fractions of FAU digesta. Results observed in vivo and in vitro suggest that NO 3 - and NO 2 - are more rapidly metabolised in the presence of rumen protozoa. Defaunated sheep may have an increased risk of NO 2 - poisoning due to NO 2 - accumulation in the rumen.

Dietary nitrate metabolism and enteric methane mitigation in sheep consuming a protein-deficient diet

It was hypothesised that the inclusion of nitrate (NO3–) or cysteamine hydrochloride (CSH) in a protein deficient diet (4.8% crude protein; CP) would improve the productivity of sheep while reducing enteric methane (CH4) emissions. A complete randomised designed experiment was conducted with yearling Merino sheep (n = 24) consuming a protein-deficient wheaten chaff control diet (CON) alone or supplemented with 1.8% nitrate (NO3–; DM basis), 0.098% urea (Ur, DM basis) or 80 mg cysteamine hydrochloride/kg liveweight (CSH). Feed intake, CH4 emissions, volatile fatty acids (VFA), digesta kinetics and NO3–, nitrite (NO2–) and urea concentrations in plasma, saliva and urine samples were measured. There was no dietary effect on animal performance or digesta kinetics (P &gt; 0.05), but adding NO3– to the CON diet reduced methane yield (MY) by 26% (P = 0.01). Nitrate supplementation increased blood MetHb, plasma NO3– and NO2– concentrations (P &lt; 0.05), but there was no indication of NO2– toxicity. Overall, salivary NO3– concentration was greater than plasma NO3– (P &lt; 0.05), indicating that NO3– was concentrated into saliva. Our results confirm the role of NO3– as an effective additive to reduce CH4 emissions, even in a highly protein-deficient diet and as a source of additional nitrogen (N) for microbial protein synthesis via N-recycling into saliva and the gut. The role of CSH as an additive in low quality diets for improving animal performance and reducing CH4 emissions is still unclear.