Full adoption of the most effective strategies to mitigate methane emissions by ruminants can help meet the 1.5 °C target by 2030 but not 2050

Plant secondary metabolites in beef cattle diets affect reactive nitrogen and greenhouse gas emissions during manure soil application: A laboratory incubation

Feed additives in beef cattle diets can reduce enteric greenhouse gas (GHG) emissions. However, subsequent effects on soil carbon (C) and nitrogen (N) after land application of manure from additive-fed animals remain largely unknown. In this study, manure (mainly feces) from beef cattle fed either an un-supplemented diet (UN) or a diet containing one of two essential oil-based feed additives, Agolin® (AG; 1 g/steer/day) or Mootral® (MT; 23.5 g/steer/day), were collected and applied to soils with different textures (clay or sandy loam). The soil-feces mixtures were incubated in a completely randomized block design at two moisture levels, 50 % and 90 % water holding capacity (WHC). The AG treatment, versus MT and UN, yielded lower cumulative mineralized N (Nmin; p < 0.01) in clay at 90 % WHC, but not at 50 % WHC. Similarly, AG, versus MT and UN, had lower carbon dioxide (CO2) emissions in clay at 90 % WHC (p < 0.01), but higher emissions in sandy loam at 90 % WHC (p < 0.01). There were no differences in CO2 among treatments at 50 % WHC. Nitrous oxide (N2O) emissions were only affected by soil type (p = 0.01) regardless of soil moisture or feed additives. Methane (CH4) emissions were affected by soil moisture (p = 0.03) and the interaction soil × moisture × manure (p < 0.01), however the feed additives had no effect. These findings indicate that the feed additives tested may affect C dynamics and Nmin in a soil and/or moisture-dependent manner.

Effect of supplementing high-fiber or high-starch concentrates or a 50:50 mix of both to late-lactation dairy cows fed cut herbage on methane production, milk yield, and ruminal fermentation

High-fiber and high-starch concentrates are used as supplements to meet the energy demand of lactating cows or to fill herbage shortage in pastoral systems. Additionally, concentrates can be a tool to mitigate enteric methane (CH4) per unit of DMI (CH4 yield) and per unit of milk production. This study aimed to compare the effects of supplementing herbage-fed late-lactation dairy cows with high-fiber (FIB), high-starch (STA), or a 50:50 mix of both concentrates (MIX) compared with no supplementation (CON) on CH4 emission parameters and ruminal fermentation. Multiparous cows (Friesian × Jersey, average ± SD; 3.8 ± 0.8 yr old; 519 ± 50 kg BW, 211 ± 10 DIM; n = 32) were blocked by lactation number and then randomly allocated to receive (on a DM basis) the following: 0 kg/d of concentrate (CON), 5 kg/d of STA, 5 kg/d of FIB, or 5 kg/d of MIX (2.5 kg each of STA and FIB). After at least 14 d of diet adaptation, the CH4 emissions, DMI, and milk production were measured in respiration chambers for 48 h, ruminal fluid was collected after chamber measurements, and short-chain fatty acids (SCFA) were analyzed. Daily milk production was recorded, and milk samples were analyzed for milk composition. The CH4 production (g/d) tended to be greater in concentrate-fed cows than CON cows. The CH4 yield was similar across the dietary treatments. The CH4 per kg of TS (calculated as fat plus protein production) was 22% less and tended to be up to 24% less per kg of fat- and protein-corrected milk (FPCM) in concentrate-fed cows than CON cows mainly due to an increase in FPCM production. After morning and afternoon feeding, the time to reach peak CH4 emissions was less in concentrate-fed cows than CON cows. The variation in the CH4 emission rate after morning feeding was greater in concentrate-supplemented cows than CON cows. The ruminal SCFA profile was similar among treatments. Regardless of the dietary treatment, the acetate plus butyrate to propionate plus valerate ratio was positively associated with CH4 yield, FPCM, and peak CH4 emission rate and negatively associated with the CH4 decline rate after peak emissions. High-starch, high-fiber, or mixed (50:50) concentrates trended to reduce the CH4 per unit of FPCM by up to 24% in lactating cows eating fresh herbage as a basal diet.

Optimizing carbon and nitrogen cycles towards net-zero greenhouse gas emissions in agrifood systems: a case study in Quzhou, China

Agrifood systems emit substantial amounts of greenhouse gases (GHG) into the atmosphere, but simultaneously sequester carbon (C) originating from atmospheric CO2 in soils. Their net effects on the GHG balance are rarely documented. This study aimed to quantify C cycles and GHG emissions in agrifood systems at both village and county levels and explore the potential to transition towards net-zero emissions. We integrated a modified material and nutrient flow model (NUFER) and a soil C cycle model (RothC) to calculate C cycles in the case area of Quzhou, China. Results showed that net photosynthesis predominantly contributed to C input to the agrifood system, while soil respiration and microbial respiration during manure storage accounted for most of the C output at all village types. Net CO2 emissions from the agrifood system in Quzhou were positive because the amount of C sequestration in soils (819 kg C ha-1 yr-1) could not offset CO2 emissions (847 kg C ha-1 yr-1) from fossil fuels used in the agrifood system, despite village-level variations. Scenario analysis demonstrated that the system could achieve net-zero CO2 emissions by adopting good management practices and recycling organic wastes. In addition to these measures, achieving net-zero GHG emissions may necessitate replacing fossil fuels with clean energy. Policies and incentives to promote net-zero emissions and circular agriculture can be mutually reinforcing. This is the first study quantifying C cycles in an entire agrifood system as well as its net CO2 and GHG emissions, facilitating the transition towards net-zero emissions and climate neutrality.

Effects of feeding 3-nitrooxypropanol for methane emissions reduction on income over feed costs in the United States

Dairy cows contribute to climate change primarily through enteric methane (CH4) emissions. Several mitigating strategies have been evaluated, including the inhibitor 3-nitrooxypropanol (3-NOP). Our objectives were to (1) evaluate the effect of feeding 3-NOP in dairy diets on lactation performance and income over feed costs (IOFC) per cow and per farm, and (2) discuss the potential implications for dairy producers. Data from 15 articles (16 experiments) met the selection criteria, with a total of 412 lactating cows used. The analysis calculated the mean difference data from the 3-NOP treatment mean minus the control treatment mean from that of the NOP-supplemented group. A mixed effects model was fitted to the data. The model included 3-NOP supplementation as fixed effect, and study as a random effect. The 3-NOP dose (mg/kg DM) was included as an explanatory variable. The presence of bias was evaluated by Egger's test, but no publication biases were observed for any of the responses of interest. Income over feed costs per cow per day was calculated based on statistically significant changes in feed consumption, milk yield, and values of milk fat and protein produced less costs for diets feeding 3-NOP. The effects of changes in IOFC were evaluated for herds with different numbers of milking cows (100, 250, and 1,000 lactating cows). Dairy cows fed 3-NOP had 0.5 kg/d lower DMI and a reduction in milk yield of 0.7 kg/d compared with control cows. Milk fat and protein yields were unaffected for dairy cows supplemented with 3-NOP compared with control. Similarly, the ECM yield and feed efficiency were unaffected for dairy cows supplemented with 3-NOP compared with control. However, dose of 3-NOP was negatively associated with the 3-NOP effect size on these performance-related parameters. Feeding 3-NOP caused a reduction of 27.9% for CH4 production at an average 3-NOP dose of 80.3 mg/kg DM. Given changes in DMI, milk yield, and milk fat and protein, supplementation of 3-NOP decreased mean IOFC by $0.35 cow-1/d-1 for a cow producing 39 kg/d. These effects on IOFC indicate that under present economic conditions, dairy farmers will need to be compensated by participation in carbon credits programs, provided other incentives for emissions reduction, or both. Reduction of methane emissions with 3-NOP supplementation requires compensation of -$128,320/yr for a dairy with 1,000 milking cows. In addition, the breakeven compensation for use of 3-NOP varied from -$0.42 cow-1/d-1 to -$0.21 cow-1/d-1 based on feed and milk component values from 2014 to 2023. Future research is warranted to evaluate long-term effects of feeding 3-NOP on the productivity of dairy cows.

Exploring the frontier of bovine protein production within territorial net zero emission targets

Global and national environmental targets for the Agriculture, Forestry and Other Land Use (AFOLU) sector need to be reconciled with increasing food and protein demands of a growing global population. Meeting climate targets in AFOLU is a tremendous challenge in countries with high ruminant livestock production and small forest carbon sinks. Using GOBLIN, an integrated assessment model that utilises a back-casting approach, 2187 future AFOLU configuration scenarios are explored to investigate whether current levels of bovine protein production in Ireland are compatible with net zero greenhouse gas (GHG) emissions by 2050. Seven proven GHG mitigation measures are combined at three levels of ambition and screened according to three definitions of net zero based on the GWP100 metric, with a focus on the integration of clover-based grasslands. Net zero was achieved in 19 % of scenarios when all GHGs require balancing by 2050. The current livestock herd configuration was incompatible with net zero, which required at least 1.5 million ha of grassland to be diverted from livestock production towards climate-positive land uses, including afforestation of close to 10 % of terrestrial land area by 2050. When applying less stringent net zero definitions based on a split gas approach, up to 63 % of explored scenarios achieved net zero. Independent of net zero definition (which must be internationally fair and transparent), results indicate that bovine protein production can only be maintained through very high deployment of ambitious technical abatement measures, alongside major land use transformation requiring large-scale structural changes in the agriculture sector.

Comparison of different residual carbon dioxide formulations as a means to select feed-efficient dairy cows

Improving feed utilisation efficiency and environmental sustainability by the selection of superior animals are amongst the widely studied topics during the last decade. For the evaluation of individual's feed utilisation efficiency, residual feed intake (RFI) has become the common metric and is defined as the difference between actual and expected feed intake. Lately, a new metric for carbon dioxide (CO2) called residual CO2 (RCO2) is being developed and similarly defined as RFI. However, the partial regression coefficients for expected feed intake obtained by regressing DM intake (DMI) on energy sinks may not be biologically plausible and this could also be the case for CO2. The objective of this study was to compare RCO2 and RFI formulations calculated using different partial regression coefficients of energy sinks obtained either from regression on energy sinks or from different energy requirement formulations used nationally or internationally. The correlations between these different formulations as well as production, efficiency, and BW measurements were also calculated. Repeated daily measurements of CO2 production (n = 51 977) using two GreenFeed Emissions Monitoring system and records of DMI from 83 primiparous Nordic Red dairy cows were used. Three types of RCO2 and RFI formulations were calculated. The first was by fitting a multiple linear regression (RCO2MLR and RFIMLR) whereas the second and third were based on the Finnish energy requirement formulation (RCO2FIN and RFIFIN) and National Research Council 2021 (NRC, 2021; RCO2NRC and RFINRC), respectively. Correlations between different RCO2 and RFI formulations were lower (from 0.37 to 0.44) than the correlation between CO2 production and DMI (0.58) implying that selection based on different RFI formulations may lead to selection of different sets of animals. Selection based on RCO2 formulations would lead to improvement in energy conversion efficiency (ECE) albeit with a slightly lower rate compared to selection based on RFI formulations. However, the decline in the trend of CO2 production would be enhanced when selection is based on RCO2 rather than RFI. Of all the residual formulations studied in Finnish dairy cows, the use of RCO2FIN is preferred because it had higher favourable correlations with ECE, CO2 and methane emission per unit of energy-corrected milk. Due to its high correlation with DMI, the conventional RFI could favour cows with lower DMI, regardless of their milk production. More data are needed to further verify the correlation between CO2 production and feed intake.

Effect of Two Selected Levels of Padina gymnospora Biowaste and Enteric Methane Emission, Nutrient Digestibility, and Rumen Metagenome in Growing Sheep

A study was conducted on growing sheep to investigate the effect of two selected levels of biowaste of Padina gymnospora on feed intake, digestibility, daily enteric methane (CH4) emission, growth performance, and rumen metagenome. We randomly divided the 18 growing male sheep into three groups of six animals each. The animals were fed on a basal diet comprising finger millet straw (Eleusine coracana) and a concentrate mixture in a 35:65 ratio. The sheep in the control group (C) were offered a concentrate mixture without waste, whereas the wheat bran in the concentrate mixture in test group I (A2) and test group II (A5) was replaced (w/w) with the biowaste of Padina gymnospora at a level of 3.07 and 7.69%, respectively. The biowaste of Padina gymnospora at the above levels in concentrate constituted 2 and 5% of the diet. A significant decrease of 28.4% in daily enteric CH4 emission (g/d) was reported in the A5 group, whereas the difference in daily enteric CH4 emission between the C and A2 & A2 and A5 groups did not prove significant. The inclusion of Padina gymnospora biowaste did not affect the nutrient intake and digestibility among the groups. The inclusion of Padina gymnospora biowaste in the A5 group resulted in a significant reduction (p = 0.0012) in daily CH4 emissions compared with group C; however, no significant differences were observed in daily CH4 emissions between groups C-A2 (p = 0.0793) and A2-A5 (p = 0.3269). Likewise, the adjustment of data to CH4 emissions per 100 g of organic matter intake indicated a substantial decrease in the A5 group relative to C. The energy loss in CH4 as a percentage of GE relative to group C decreased significantly (-23.4%) in the A5 group; however, this reduction was not associated with an increase in productivity, as almost similar average daily gain (p = 0.827) was observed in the groups. The replacement of wheat bran with the biowaste of Padina gymnospora significantly decreased the numbers of total protozoa and holotrichs in the A5 group. Irrespective of the group, the Bacteroidota was the single largest phylum in the rumen metagenome, representing >60% of the microbiota. However, the abundance of Bacteroidota was similar among the groups. The methanogenic phyla Euryarchaeota was the 5th most abundant; however, it constituted only 3.14% of the metagenome. The abundance of Desulfovibrio was significantly higher in the A5 group as compared with the control. In conclusion, the significant increase in the abundance of sulfate-reducing bacteria and reduction in protozoal numbers led to a significant reduction in CH4 emissions with the incorporation of biowaste of Padina gymnospora at a 5% level of the diet.

Effects of different doses of 3-nitrooxypropanol combined with varying forage composition on feed intake, methane emission, and milk production in dairy cows

The objective of this study was to investigate the effect of combining different doses of 3-nitrooxypropanol (3-NOP) with varying forage composition on gas emission and production performance of dairy cows. Seventy-two lactating Danish Holstein cows (36 primiparous and 36 multiparous) were enrolled in a continuous randomized block design with an initial 2-wk covariate period followed by application of treatments for 12 consecutive weeks. Initial DMI and ECM yield were 23.8 ± 3.34 kg/d (mean ± SD) and 38.3 ± 7.12 kg/d, respectively. Cows were blocked according to parity and DIM. Treatments were organized in a 2 × 3 factorial arrangement. The first factor was diet type, reflecting 2 different forage compositions of the diet. The ratio of grass-clover silage to corn silage was 60%:40% of total forage DM in grass-based diets and 40%:60% in corn-based diets. In total, forage constituted 56% of the DM in the partial mixed rations. The second factor reflected 3 doses of 3-NOP: 0, 60, or 80 mg 3-NOP/kg DM. Gas emissions were measured using GreenFeed systems and feed intake by using Insentec Roughage Intake Control bins. Weekly averages from the last 10 wk were analyzed by using a mixed model including fixed effects and interactions among diet type, 3-NOP dose, week, and parity, and included a covariate term and accounted for repeated measures. Methane yield (g/kg DMI) was reduced by 34% and 31%, and CH4 intensity (g/kg ECM) was reduced by 34% and 32% at 60 and 80 mg 3-NOP/kg DM, respectively, and we found no difference in CH4 yield or intensity between the 2 doses. The corn- and grass-based diets were similar in NDF and starch levels, and we found no interaction between dose of 3-NOP and diet type for CH4 yield or intensity. Total DMI was reduced by 9% in cows fed 80 mg 3-NOP/kg DM across diet types, whereas we found no effect on DMI at 60 mg 3-NOP/kg DM. Similarly, ECM yield was reduced by 5% in cows fed 80 mg 3-NOP/kg DM compared with no 3-NOP supplementation, and these cows had a 42% lower BW increase over the experiment compared with no supplementation. In conclusion, 3-NOP at 60 mg/kg DM was efficient in reducing CH4 without compromising feed intake and milk production, whereas 80 mg 3-NOP/kg DM negatively affected production performance.

Effect of increasing dietary fat by feeding 15% whole cottonseed on milk production, total-tract digestibility, and methane emission in dairy cows

Whole cottonseed (WCS) is fed as a source of fat, protein, and fiber. Cottonseed is high in unsaturated fatty acids (FA) but is considered lower risk for biohydrogenation-induced milk fat depression because it is slowly released in the rumen. Unsaturated FA have been reported to decrease methane emissions in some experiments, but the effect of FA source is unclear. The objective of the current experiment was to investigate the effect of FA from WCS on milk and methane production and total-tract nutrient digestibility. Sixteen multiparous cows were arranged in a crossover design with 21-d periods. Treatments were 15% WCS substituted for a mixture of cottonseed hulls and soybean meal. Cottonseed had no effect on DMI and milk yield (MY) but increased milk fat concentration (0.2 percentage units) and yield (110 g/d). Cottonseed also decreased the concentration of FA <16 C and 16 C in milk fat and increased FA >16 C and trans-10 18:1 and trans-11 18:1. Increasing dietary fat had no effect on the efficiency of transfer of 18 C FA to milk. There was no effect on milk protein concentration and yield. Whole cottonseed decreased apparent total-tract digestibility of OM and DM due to a decline in NDF digestibility, but less than 3% of seeds consumed were recovered intact in the feces. Whole cottonseed increased digestibility of 16 C FA, but the digestibility of total and 18 C FA were not changed. The production (g/d), yield (g/kg of DMI), and intensity (g/kg of MY or ECM) of H2, CH4, and CO2 were not changed with WCS. Plasma total gossypol and the positive and negative isomers increased with WCS but were below toxic levels. In conclusion, increasing dietary UFA by feeding 15% WCS increased milk fat yield through an increased supply of preformed FA and did not affect methane production under these dietary conditions.

The effect of Rumin8 Investigational Veterinary Product-a bromoform based feed additive-on enteric methane emissions, animal production parameters, and the rumen environment in feedlot cattle

The livestock sector plays a crucial role in mitigating global climate change by reducing greenhouse gas emissions, with enteric fermentation as the largest source. Although various approaches have been proposed to decrease enteric methane (CH4) emissions, feed additives containing bromoform (CHBr3) have shown promise with minimal impact on animal production parameters. This study aimed to evaluate the effects of two Rumin8 Investigational Veterinary Products (IVP) containing synthetic CHBr3 on enteric gas emissions, animal production parameters, and the rumen environment. Twenty-four Angus beef steers were randomly assigned to one of three treatment groups: Control, Oil (8 mL Rumin8 oil IVP/kg DMI), and Powder (1.2 g Rumin8 powder IVP/kg DMI). The Rumin8 oil IVP treatment resulted in a CHBr3 intake of 32.2 mg/kg DMI, while the Rumin8 powder IVP provided a CHBr3 intake of 2.0 mg/kg DMI during weeks 1-8. In week 9, a new batch of Rumin8 powder IVP increased the CHBr3 intake to 17.9 mg/kg DMI. The Oil group exhibited 95.0%, 95.0%, and 96.1% reductions in CH4 production (g/day), yield (g/kg DMI), and intensity (g/kg average daily gain), respectively, accompanied by 925%, 934%, and 858% increases in H2 production, yield, and intensity, respectively. Neither treatment significantly affected animal production parameters or rumen environment variables. These findings suggest that Rumin8 oil IVP containing synthetic CHBr3 has the potential to reduce enteric CH4 emissions. This warrants further investigation, as this is the first published in vivo study to assess compound efficacy.

Hotspot Analysis of Rumen Microbiota and Methane Mitigation in Ruminants: A Bibliometric Analysis from 1998 to 2023

Methane (CH4) is the second-most abundant greenhouse gas, following carbon dioxide (CO2), and has a warming potential 28 times greater than CO2 [...].

Reduction of enteric methane emission using methanotroph-based probiotics in Hanwoo steers

BACKGROUND

Methane emission from enteric rumen fermentation is a main source of greenhouse gas (GHG) emission and a major concern for global warming.

RESULTS

In this study, we isolated methanotroph-methylotroph consortium NC52PC from the rumen after a series of sub-culture and repetitive streaking on an agar plate and polycarbonate membrane filter. The NC52PC comprises methanotroph species (Methylocystis sp.) and methylotroph species (Methylobacterium sp.), forming a consortium capable of growing solely on methane as a carbon source. Their morphology, growth, and genome sequence were characterized. We assessed its effectiveness in mitigating methane emissions through both in vitro and in vivo experiments. During the in vitro trial, the introduction of NC52PC (at a concentration of 5.1 × 107 CFUs/ml) demonstrated a reduction in methane production exceeding 40% and 50% after 12 and 24 h, respectively. Also, NC52PC did not significantly alter other aspects of the in vitro rumen fermentation parameters such as pH, total gas production, and digestibility. Further investigation involved testing NC52PC as a dietary supplement in 12 young Hanwoo steers over three 30-day test periods. The steers received a diet comprising 70.8% concentrate and 29.2% bluegrass on a dry matter basis, with variations including 3 × 107 CFUs/ml of NC52PC (LOW) and 3 × 108 CFUs/ml (HIGH) of NC52PC, and without NC52PC as a control (CON). Steers administered with HIGH and LOW concentrations of NC52PC exhibited reduced enteric methane emission (g/day) by 14.4% and 12.0%, respectively.

CONCLUSION

Feeding methanotroph-methylotroph consortium NC52PC significantly reduced methane emissions in Korean beef cattle without any adverse effects on animal health. These findings suggest that this probiotic could serve as a promising feed additive to effectively mitigate methane emissions from ruminants. However, further research is needed to evaluate the long-term effects of NC52PC on animal health, and on meat and milk quality.

The Path to Net-Zero in Dairy Production: Are Pronounced Decreases in Enteric Methane Achievable?

Achieving net-zero greenhouse gas (GHG) emissions in dairy production will require >50% reduction in enteric methane (CH4) emissions together with elimination of emissions from feed production, additional carbon sequestration, reduction in manure emissions, anaerobic digestion of manure, and decreased reliance on fossil fuel energy. Over past decades, improved production efficiency has reduced GHG intensity of milk production (i.e., emissions per unit of milk) in the United States, but this trend can continue only if cows are bred for increased efficiency. Genetic selection of low-CH4-producing animals, diet reformulation, use of feed additives, and vaccination show tremendous potential for enteric CH4 mitigation; however, few mitigation strategies are currently available, and added cost without increased revenue is a major barrier to implementation. Complete elimination of CH4 emissions from dairying is likely not possible without negatively affecting milk production; thus, offsets and removals of other GHGs will be needed to achieve net-zero milk production.

The role of rumen microbiome in the development of methane mitigation strategies for ruminant livestock

Ruminants play an important role in global food security and nutrition. The rumen microbial community provides ruminants with a unique ability to convert human indigestible plant matter, into high quality edible protein. However, enteric CH4 produced in the rumen is both a potent GHG and a metabolizable energy loss for ruminants. As the rumen microbiome constitutes 15-40% of the inter-animal variation in enteric CH4 emissions, understanding the microbiological mechanisms underpinning ruminal methanogenesis and its interaction with the host animal, is crucial for developing CH4 mitigation strategies. Variation in the relative abundance of different microbial species has been observed in cattle with contrasting residual CH4 emission and CH4 yield with up to 20% of the variation in inter-animal CH4 emissions attributable to the presence of a small number of microbial species. The demonstration of ruminotypes associated with high or low CH4 emissions suggests that interactions within complex microbial consortia and with their host are a major source of variation in CH4 emissions. Consequently, microbiome-assisted genomic approaches are being developed to select low CH4 emitting cattle, with breeding values for enteric CH4 being included as part of national breeding programmes. Generating rumen microbiome data for use in selection programs is expensive, therefore, identifying microbial biomarkers in milk or plasma to develop predictive models which include microbial predictors in equations based on animal related data, is required. A better understanding of the rumen microbiome has also aided the development and refinements of anti-methanogenic feed additives. However, these strategies, which increase the amount of reducing equivalents in the rumen ecosystem, do not generally result in an enrichment of propionate or an improvement in animal performance. Current research aims to provide alternative sinks to reducing equivalents and to stimulate activity of commensal microbes or the supplementation of direct fed microbials to capture lost energy. Furthering our knowledge of the rumen microbiome and its interaction with the host, will aid in the development of CH4 mitigation strategies for ruminant livestock.

Dynamic Methane Emissions from China's Fossil-Fuel and Food Systems: Socioeconomic Drivers and Policy Optimization Strategies

In response to the 2023 "Action Plan for Methane Emission Control" in China, which mandates precise methane (CH4) emission accounting, we developed a dynamic model to estimate CH4 emissions from fossil-fuel and food systems in China for the period 1990-2020. We also analyzed their socioeconomic drivers through the Logarithmic Mean Divisia Index (LMDI) model. Our analysis revealed an accelerated emission increase (850.4 Gg/year) during 2005-2015, compared to 570.4 Gg/year in the preceding period (1990-2005), with a downward trend (-1216.6 Gg/year) detected after 2015. The fossil-fuel system was the primary contributor to these changes, with emissions positively correlated with per capita GDP and negatively influenced by energy intensity at the production stage and wastewater discharge intensity at the disposal stage. In the food system, CH4 emission intensity and waste treatment practices were the most significant negative drivers at production and disposal stages, respectively. Urbanization also played a notable role, contributing to 19.3% and 18.1% in livestock and rice cultivation emission reductions, respectively. Despite the observed changes, coal mining, livestock, and rice remain the dominant sources of CH4 emissions. Our findings suggest that effective CH4 emission mitigation can be achieved through strategies such as reducing energy intensity, improving agricultural production efficiency, and advancing urbanization efforts.

Anti-Methanogenic Potential of Seaweeds and Impact on Feed Fermentation and Rumen Microbiome In Vitro

A series of in vitro studies were conducted to explore the anti-methanogenic potential of five seaweeds collected from the Indian sea and to optimize the level(s) of incorporation of the most promising seaweed(s) into a straw and concentrate diet to achieve a significant reduction in methane (CH4) production without disturbing rumen fermentation characteristics. A chemical composition analysis revealed a notable ash content varying between 55 and 70% in seaweeds. The crude protein content was highly variable and ranged between 3.25 and 15.3% of dry matter. Seaweeds contained appreciable concentrations of tannins and saponins. Among the seaweeds, Spyridia filamentosa exhibited significantly higher CH4 production, whereas the percentage of CH4 in total gas was significantly lower in the cases of Kappaphycus alvarezii and Sargassum wightii. The ranking of seaweeds in terms of CH4 production (mL/g OM) is as follows: Sargassum wightii < Kappaphycus alvarezii < Acanthophora specifera < Padina gymnospora < Spyridia filamentosa. A remarkable decrease of 31-42% in CH4 production was recorded with the incremental inclusion of Kappaphycus alvarezii at levels of 3-5% of the dry matter in the diet. The addition of Sargassum wightii led to a significant decrease of 36-48% in CH4 emissions when incorporated at levels of 4-5% of dry matter, respectively. The findings of this study revealed a significant decrease in the numbers of total protozoa and Entodinomorphs, coupled with increasing abundances of sulfate-reducing microbes and minor methanogens. Metagenome data revealed that irrespective of the seaweed and treatment, the predominant microbial phyla included Bacteroidota, Bacillota, Pseudomonadota, Actinomycetota, Fibrobacterota, and Euryarchaeota. The prevalence of Methanobrevibacter was similar across treatments, constituting the majority (~79%) of the archaeal community. The results also demonstrated that the supplementation of Kappaphycus alvarezii and Sargassum wightii did not alter the feed fermentation pattern, and therefore, the reduction in CH4 production in the present study could not be attributed to it. Animal studies are warranted to validate the extent of reduction in CH4 production and the key processes involved by supplementation with Kappaphycus alvarezii and Sargassum wightii at the recommended levels.

Effects of cashew nutshell extract inclusion into a high-grain finishing diet on methane emissions, nutrient digestibility, and ruminal fermentation in beef steers

By 2050, the U.S. beef industry must produce an extra 40 million tons of beef to satisfy the global demand. Such an increase in inventory will undoubtedly enhance methane (CH4) production from livestock, which should be reduced by over 20%. The addition of plant secondary metabolites, such as anacardic acid present in cashew nutshell extract (CNSE), has shown promising results in reducing CH4 yield, although its effects seemed to be diet-dependent. This study evaluated the addition of CNSE to a high-grain diet (85:15 grain:forage) on in vivo CH4 emissions, nutrient digestibility, performance, feeding behavior, and ruminal fermentation parameters of beef steers. Sixteen Angus crossbred steers [599 ± 40 kg of bodyweight (BW)] and 6 ruminally cannulated crossbred steers (490 ± 51 kg of BW) were utilized in a crossover design with 2 experimental periods of 56 d each, composed by 14 d of adaptation, 35 d of measurement, and 7 d of washout. Following adaptation, steers were sorted by BW, and assigned to receive no additive (CON) or CNSE at 5 g/steer/d. Data were analyzed using the MIXED procedure of SAS. Inclusion of CNSE increased (P < 0.05) propionate concentration and molar proportion (MP; mol/100 mol), tended to decrease acetate MP (P = 0.10), reduced the acetate:propionate (A:P) ratio (P = 0.05), and MP of branched-chain volatile fatty acids (P < 0.01). Neither in vitro organic matter digestibility nor in vitro CH4 yield were affected by CNSE inclusion (P > 0.05). Steers receiving CNSE exhibited greater (P < 0.05) final BW, dry matter intake (DMI), and average daily gain (ADG) but lesser (P < 0.05) in vivo CH4 emission rate (g/d), yield (g/kg of DMI), and intensity (g/kg of ADG). Meal length, bunk visit duration, and apparent total tract digestibility of DM increased (P < 0.05) after CNSE addition. Considering CNSE-supplemented steers spent more time in the feedbunk and exhibited higher DMI, CH4 mitigation was unlikely associated with intake reduction. The addition of CNSE to a high-grain diet in beef steers demonstrated significant improvements in animal performance and reduced CH4 emissions, as the result of shifts in ruminal fermentation patterns, favoring propionate instead of acetate concentration, leading to a reduction in the A:P ratio. CNSE shows promise as a strategy to enhance beef industry sustainability.

Effects of dietary supplementation with linseed oil, Ascophyllum nodosum or treated A. nodosum on animal performance, gaseous emissions, ruminal fermentation and microbiota, and meat quality in growing dairy-beef bulls

Oils high in polyunsaturated fatty acids (PUFA) and seaweeds containing phlorotannins have potential anti-methanogenic effects in ruminants. This study assessed the potential of dietary supplementation with linseed oil, Ascophyllum nodosum or treated A. nodosum in an intensive beef cattle feeding system on animal performance, gaseous emissions, ruminal fermentation and microbiota, and muscle fatty acid profiles. Seventy-two dairy-beef bulls (380 kg; 11 mo of age) were randomly allocated to one of four dietary treatments (n = 18) for a 70-d period. The diet consisted of a 60:40 grass silage:concentrate ratio. Silage was offered daily (0900 hours) and concentrates were offered twice daily (0800 and 1500 hours). Dietary treatments were incorporated into the concentrate portion of the diet as follows; 1) CON (no supplementation), 2) LSO (linseed oil), 3) SW (A. nodosum), and 4) EX (A. nodosum extract), included to target 0%, 4%, 2%, and 2% of dry matter intake (DMI), respectively. The concentrates were formulated to be isonitrogenous across the 4 treatment groups. Total DMI (American Calan Inc., Northwood, NH), average daily gain (ADG), gain:feed, and enteric emissions (GreenFeed; C-Lock Inc., Rapid City, SD) were measured for the 70-d supplementation period. Total DMI (P = 0.17), ADG (P = 0.28), gain:feed (P = 0.68), and total tract digestibility (P = 0.70) did not differ across treatments. Daily methane production (P < 0.001) for CON, LSO, SW, and EX was 210, 170, 202, and 193 g/d, respectively, resulting in reductions of 19% and 8% for LSO and EX, respectively, relative to CON. Ruminal fermentation parameters show that LSO was the only dietary treatment to increase propionate (P = 0.09) and decrease butyrate (P = 0.04) concentrations relative to CON. Microbial analyses showed LSO supplementation increased and decreased relative abundances of fungal genera Buwchfawromyces and Piromyces, respectively, while altering relative abundances of the bacterial genera Muribaculaceae, Bacteroidales RF16 group and Bacterium F082. Additionally, LSO increased linolenic acid (P < 0.001) and n-3 PUFA (P < 0.001) concentration of the longissimus dorsi muscle compared to CON, SW, and EX. In conclusion, LSO was the most effective dietary supplementation strategy compared to CON, EX, and SW, whereby it reduced methane emissions, modified ruminal fermentation and microbial profiles, and enhanced beneficial muscle PUFA concentration, without impacting animal performance.

Feed additives for methane mitigation: Regulatory frameworks and scientific evidence requirements for the authorization of feed additives to mitigate ruminant methane emissions

This article describes the regulatory and evidence requirements necessary for the authorization of antimethanogenic feed additives (AMFA) aimed at mitigating enteric methane (CH4) emissions from ruminants. It outlines the legislation and legal procedures in Australia, Canada, the European Union, New Zealand, South Korea, the United Kingdom, and the United States as illustrative examples, offering insights for applicants seeking authorization. Additionals objectives are to highlight consequential similarities and differences in regulations and evidence requirements and offer recommendations for scientists and applicants. The pivotal role that scientific evidence plays in the evaluation and approval processes is emphasized, along with the need for applicants and researchers to understand and adhere to the specific regulations of each jurisdiction. Feed additives are regulated to ensure their safety for animals, humans, and the environment, and to verify their effectiveness for the intended use of enteric CH4 mitigation. Regulations cover various aspects, including ingredient safety, manufacturing practices, product labeling, and the establishment of permissible limits for certain substances to ensure their safe use in animal feed. Compliance with these regulations is mandatory, and they are enforced by regulatory agencies within each jurisdiction, aiming to protect animal health, promote food safety, and prevent misleading claims and unsafe practices. The assessment processes involve evaluating scientific evidence submitted by applicants, along with evaluations of quality control procedures, and record-keeping practices. The major difference in regulations is that each jurisdiction developed unique criteria to legally classify AMFA, making it challenging to satisfy all legal classifications with a single set of criteria for scientific evidence. However, numerous similarities and a universal reliance on the concept of intended use indicate consistency across all jurisdictions on the need for robust evidence for efficacy, safety, and product quality and documentation even if the type, size, duration, and location of the studies they require differ. Recommendations are made for both scientists and applicants, emphasizing the importance of designing, conducting, and reporting scientific evaluations transparently, using validated standards and methods, and communicating with regulatory bodies to ensure compliance with regulations and evidence requirements.

Global natural and anthropogenic methane emissions with approaches, potentials, economic costs, and social benefits of reductions: Review and outlook

The increase in atmospheric methane (CH4) level directly contributes to approximately one-fifth of global mean temperature rise since preindustrial era, only next to CO2. Global anthropogenic CH4 emissions has augmented by nearly three-fifths during the past five decades; due to climate change, natural CH4 emissions are plausibly projected to increase in the foreseeable future. Thereby, examining and projecting long-term natural and anthropogenic CH4 emissions and sinks are imperative. According to peer-reviewed literatures as information sources for this compendium, we recapitulate natural and anthropogenic CH4 emissions, summarize available abatement approaches and their mitigation potentials, and investigate and encapsulate economic costs and social benefits of reductions. We list current challenges in realizing CH4 emissions reductions and suggest possible technical pathways for future mitigation.

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: Modeling the impact of feed additives on enteric methane emission of ruminants-Approaches and recommendations

Over the past decade, there has been considerable attention on mitigating enteric methane (CH4) emissions from ruminants through the utilization of antimethanogenic feed additives (AMFA). Administered in small quantities, these additives demonstrate potential for substantial reductions of methanogenesis. Mathematical models play a crucial role in comprehending and predicting the quantitative impact of AMFA on enteric CH4 emissions across diverse diets and production systems. This study provides a comprehensive overview of methodologies for modeling the impact of AMFA on enteric CH4 emissions in ruminants, culminating in a set of recommendations for modeling approaches to quantify the impact of AMFA on CH4 emissions. Key considerations encompass the type of models employed (i.e., empirical models including meta-analyses, machine learning models, and mechanistic models), the modeling objectives, data availability, modeling synergies and trade-offs associated with using AMFA, and model applications for enhanced understanding, prediction, and integration into higher levels of aggregation. Based on an evaluation of these critical aspects, a set of recommendations is presented concerning modeling approaches for quantifying the impact of AMFA on CH4 emissions and in support of farm-level, national, regional, and global inventories for accounting greenhouse gas emissions in ruminant production systems.

Feed additives for methane mitigation: Recommendations for identification and selection of bioactive compounds to develop antimethanogenic feed additives

Despite the increasing interest in developing antimethanogenic additives to reduce enteric methane (CH4) emissions and the extensive research conducted over the last decades, the global livestock industry has a very limited number of antimethanogenic feed additives (AMFA) available that can deliver substantial reduction, and they have generally not reached the market yet. This work provides technical recommendations and guidelines for conducting tests intended to screen the potential to reduce, directly or indirectly, enteric CH4 of compounds before they can be further assessed in in vivo conditions. The steps involved in this work cover the discovery, isolation, and identification of compounds capable of affecting CH4 production by rumen microbes, followed by in vitro laboratory testing of potential candidates. The finding of new bioactive compounds as AMFA can be based on 2 approaches: empirical and mechanistic. The empirical approach involves obtaining and screening compounds present in databases and repositories that potentially possess the desired effect but have not yet been tested, screening natural sources of secondary compounds such as plants, fungi, and algae for their antimethanogenic effects, or examining compounds with antimethanogenic effect on microbes in other research domains outside the rumen. In contrast, the mechanistic approach is the theoretical process of discovery new bioactive compounds based on existing knowledge of a biological target or process. The in vitro methodologies reviewed include examining effects at the subcellular level, in single pure cultures of methanogens and examining in more complex mixed rumen microbial populations. Simple in vitro methodologies (subcellular assessments and batch culture) allow testing a large number of compounds, whereas more complex systems simulating the rumen microbial ecosystem can test a limited number of candidates but provide better insight about the antimethanogenic efficacy. This work collated the main advantages, limitations, and technical recommendations associated with each step and methodology use during the identification and screening of AMFA candidates.

Effect of dietary fat source and concentration on feed intake, enteric methane, and milk production in dairy cows

Dietary fat can be used in dairy cow nutrition to reduce enteric methane (CH4), but studies with multiple dietary fat concentrations are scarce. Among fat sources, rapeseed is easily accessible in Europe and North America, and palm kernel fat has been shown to be a potent inhibitor of ruminal methanogenesis. Forty-eight cows (half primiparous and half multiparous) were used in a 6 × 6 Latin square design, with 6 periods of 21 d each. Six treatments were used: a control, 3 fat concentrations (low, medium, and high) of rapeseed (RS), and 2 fat concentrations (low and medium) of palm kernel fatty acids (PK). The total crude fat concentrations ranged from 3% to 7% of DM. The cows were fed the treatments as a partial mixed ration, and they received additional concentrate from the GreenFeed units (1 unit for 12 cows) used to measure CH4 production. Increased dietary crude fat concentration of both RS and PK reduced DMI. The reduction in DMI was stronger in cows fed medium concentration of PK than for any RS concentration, which was comparable to previous studies for both RS and PK. Digestibility of OM was highest at low fat concentration of both fat sources, and lowest at high RS concentration. Digestibility of NDF was reduced by 2 percentage units when cows were fed medium PK concentration instead of the control treatment. Rapeseed supplementation with dietary crude fat up to 5.7% of DM increased milk and ECM yields, but the equivalent PK concentration reduced ECM. Increased fat supplementation decreased CH4 yield (g CH4/kg of DMI) linearly when RS was used, and quadratically when PK was used. The medium PK concentration reduced CH4 yield more than medium RS concentration, but there was no difference for CH4 intensity (g CH4/kg of ECM). Rapeseed fat supplementation with dietary crude fat above 5.7% of DM could reduce further CH4 yield, but fat supplementation was not accompanied by an increase in productivity. The fat source must be accounted for when considering enteric methane reduction, as the PK provided stronger effect than RS, but the associated reduction in milk production did not support the use of PK for methane reduction.

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.

Feed additives for methane mitigation: Assessment of feed additives as a strategy to mitigate enteric methane from ruminants-Accounting; How to quantify the mitigating potential of using antimethanogenic feed additives

Recent advances in our understanding of methanogenesis have led to the development of antimethanogenic feed additives (AMFA) that can reduce enteric methane (CH4) emissions to varying extents, via direct targeting of methanogens, alternative electron acceptors, or altering the rumen environment. Here we examine current and new approaches used for the accounting (i.e., quantification) of enteric CH4 abatement by the use of AMFA in the livestock sector from the individual animal to the global scale. Along with this process, recommendations are provided on how to account for the mitigation potential at the animal level, as well as in farm-scale models, emissions trading schemes, life cycle assessment, and carbon (C) footprinting tools, and in regional and national inventories. In addition, an assessment of uncertainties and potential trade-offs and off-setting with the use of AMFA (i.e., efficacy vs. effectiveness, upstream and downstream emissions) is provided. The accounting of on-farm enteric CH4 emissions and benefits from the use of AMFA starts with the ruminant animal (with estimates obtained from a range of approaches, from simple empirical emission factors or equations to complex process-based models) and goes all the way to national and supranational accounting. The choice of methodologies and levels of complexity to account for mitigation of enteric CH4 (or total GHG) emissions in livestock systems must be tailored to the scale of analysis aimed, the availability of input data to represent contextualized conditions, and the accounting objectives (e.g., academic exercise vs. producer's GHG certification vs. national GHG inventory). The accounting of enteric CH4 mitigating effects needs to consider the AMFA delivery methods and synergies and trade-offs of GHG emissions at levels before and beyond (upstream and downstream) the animal to fully assess the impact of AMFA use. At large, the accounting of methane abatement by feed additives remains to be fully assessed beyond experimental results (efficacy) to address pragmatism (effectiveness), potential for adoption, and societal acceptance.

In silico docking and molecular dynamics for the discovery of inhibitors of enteric methane production in ruminants - A review

The increase in methane emissions, a major greenhouse gas, threatens human well-being and global ecosystems due to its contribution to global warming. Livestock, particularly ruminants, have been a major research topic in recent decades due to their methane production. Therefore, the objective of the current review was to comprehensively discuss the in silico techniques used to mitigate methane production from ruminants. The review covers the principles of in silico docking and molecular dynamics, which can be used to develop methanogenesis inhibitors. It also discusses specific methanogen enzymes as potential targets for inhibitor development. Furthermore, in silico-based methanogenesis inhibitor development studies have been reviewed with the authors' opinions. The further use of in silico-based research techniques, including artificial intelligence-based systems, is encouraged to help reduce methane production from livestock more efficiently and costeffectively.

Gallic and Ellagic Acids Differentially Affect Microbial Community Structures and Methane Emission When Using a Rumen Simulation Technique

Dietary tannins can affect rumen microbiota and enteric fermentation to mitigate methane emissions, although such effects have not yet been fully elucidated. We tested two subunits of hydrolyzable tannins named gallic acid (GA) and ellagic acid (EA), alone (75 mg/g DM each) or combined (150 mg/g DM in total), using the Rusitec system. EA and EA+GA treatments decreased methane production, volatile fatty acids, nutrient degradation, relative abundance of Butyrivibrio fibrisolvens, Fibrobacter succinogenes, Ruminococcus flavefaciens but increased Selenomonas ruminantium. EA and EA+GA increased urolithins A and B. Also, EA and EA+GA reduced bacterial richness, with limited effects on archaeal richness. For bacteria, Megasphaera elsdenii was more abundant after EA and EA+GA, while Methanomethylophilaceae dominated archaea in all treatments. EA was more effective than GA in altering rumen microbiota and fermentation but GA did not reduce VFA and nutrient degradation. Thus, dietary supplementation of EA-plant extracts for ruminants may be considered to mitigate enteric methane, although a suitable dosage must be ensured to minimize the negative effects on fermentation.

Evaluation of maternal bromoform supplementation in late gestation on blood parameters of cows and their progeny

Bromoform supplementation has been successful in reducing enteric methanogenesis in ruminants; however, the impacts on the health of these animals are still limited. The current study evaluates the impact of maternal bromoform supplementation on the health of late-gestation cows and their progeny. Pregnant Angus cows (n = 42) were allocated into a control or bromoform group (n = 21 cows per treatment). Bromoform extracted from Asparagopsis armata (7,372 mg/kg) was supplemented once daily. Blood samples were collected from cows before supplementation (baseline). Within 24 h of parturition, blood and colostrum samples were collected from each cow and blood from neonates. Colostrum brix was measured to indicate immunoglobulin content. All data was analysed using the MIXED procedure in SAS. Supplementation of cows with bromoform resulted in increased blood urea to creatinine ratio (P = 0.048), base excess (P = 0.049), total carbon dioxide (TCO2; P = 0.048) and a decrease in blood glutamate dehydrogenase (GLDH; P = 0.031) compared to the control group. For cows in the bromoform group, a trend was observed for higher levels of partial pressure of carbon dioxide (pCO2; P = 0.070) and bicarbonate (HCO3-; P = 0.052), and lower levels of partial pressure of oxygen (pO2; P = 0.058) compared to the control group. Blood gamma-glutamyl transferase (GGT) was elevated in offspring of cows fed bromoform (P = 0.050). The lower blood pO2 of pregnant cows fed bromoform and elevated blood GGT levels in offspring are not well understood and highlight the need for further investigation. Additionally, the low-dose bromoform supplementation affected various blood gas parameters of cows and calves, demonstrating the importance of monitoring these parameters when using different doses of halogenated compounds in livestock.

The ruminant gut microbiome vs enteric methane emission: The essential microbes may help to mitigate the global methane crisis

Ruminants release enteric methane into the atmosphere, significantly increasing greenhouse gas emissions and degrading the environment. A common focus of traditional mitigation efforts is on dietary management and manipulation, which may have limits in sustainability and efficacy, exploring the potential of essential microorganisms as a novel way to reduce intestinal methane emissions in ruminants; a topic that has garnered increased attention in recent years. Fermentation and feed digestion are significantly aided by essential microbes found in the rumen, such as bacteria, fungi, and archaea. The practical implications of the findings reported in various studies conducted on rumen gut concerning methane emissions may pave the way to understanding the mechanisms of CH4 production in the rumen to enhance cattle feed efficiency and mitigate CH4 emissions from livestock. This review discussed using essential bacteria to reduce intestinal methane emissions in ruminants. It investigates how particular microbial strains or consortia can alter rumen fermentation pathways to lower methane output while preserving the health and productivity of animals. We also describe the role of probiotics and prebiotics in managing methane emissions using microbial feed additives. Further, recent studies involving microbial interventions have been discussed. The use of new methods involving functional metagenomics and meta-transcriptomics for exploring the rumen microbiome structure has been highlighted. This review also emphasizes the challenges faced in altering the gut microbiome and future directions in this area.

A metagenomic catalogue of the ruminant gut archaeome

While the ruminant gut archaeome regulates the gut microbiota and hydrogen balance, it is also a major producer of the greenhouse gas methane. However, ruminant gut archaeome diversity within the gastrointestinal tract (GIT) of ruminant animals worldwide remains largely underexplored. Here, we construct a catalogue of 998 unique archaeal genomes recovered from the GITs of ruminants, utilizing 2270 metagenomic samples across 10 different ruminant species. Most of the archaeal genomes (669/998 = 67.03%) belong to Methanobacteriaceae and Methanomethylophilaceae (198/998 = 19.84%). We recover 47/279 previously undescribed archaeal genomes at the strain level with completeness of >80% and contamination of <5%. We also investigate the archaeal gut biogeography across various ruminants and demonstrate that archaeal compositional similarities vary significantly by breed and gut location. The catalogue contains 42,691 protein clusters, and the clustering and methanogenic pathway analysis reveal strain- and host-specific dependencies among ruminant animals. We also find that archaea potentially carry antibiotic and metal resistance genes, mobile genetic elements, virulence factors, quorum sensors, and complex archaeal viromes. Overall, this catalogue is a substantial repository for ruminant archaeal recourses, providing potential for advancing our understanding of archaeal ecology and discovering strategies to regulate methane production in ruminants.

Enteric Methane Emission in Livestock Sector: Bibliometric Research from 1986 to 2024 with Text Mining and Topic Analysis Approach by Machine Learning Algorithms

Methane (CH4) from livestock, particularly enteric CH4 emission (EME), is one contributor to greenhouse gas emissions and climate change. This review analyzed 1294 scientific abstracts on EME in ruminants from 1986 to May 2024, using Scopus® data. Descriptive statistics, text mining, and topic analysis were performed. Publications on EME have risen significantly since 2005, with the Journal of Dairy Science being the most frequent publisher. Most studies (82.1%) were original research, with Northern Hemisphere countries leading in publication numbers. The most frequent terms were "milk", "cow", and "diet", while key research topics included greenhouse gas emissions from livestock, diet composition, and prediction models. Despite progress, some areas like CH4 emission from animals need further investigation.

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.

Unraveling the genetic basis of methane emission in dairy cattle: a comprehensive exploration and breeding approach to lower methane emissions

Ruminant animals, such as dairy cattle, produce CH4, which contributes to global warming emissions and reduces dietary energy for the cows. While the carbon foot print of milk production varies based on production systems, milk yield and farm management practices, enteric fermentation, and manure management are major contributors togreenhouse gas emissions from dairy cattle. Recent emerging evidence has revealed the existence of genetic variation for CH4 emission traits among dairy cattle, suggests their potential inclusion in breeding goals and genetic selection programs. Advancements in high-throughput sequencing technologies and analytical techniques have enabled the identification of potential metabolic biomarkers, candidate genes, and SNPs linked to methane emissions. Indeed, this review critically examines our current understanding of carbon foot print in milk production, major emission sources, rumen microbial community and enteric fermentation, and the genetic architecture of methane emission traits in dairy cattle. It also emphasizes important implications for breeding strategies aimed at halting methane emissions through selective breeding, microbiome driven breeding, breeding for feed efficiency, and breeding by gene editing.

Greenhouse gas emissions from livestock: sources, estimation, and mitigation

The increase in greenhouse gas (GHG) emissions has resulted in climate change and global warming. Human activities in many sectors, including agriculture, contribute to approximately 9.2% of total GHG emissions from Annex I countries. An argument on issues of livestock being the highest contributor to GHG emissions has grown since FAO's 2006 report Livestock's Long Shadow. The issue has continued growing, conflicting the importance of the industry in terms of food security and livelihoods, thus, monitoring GHG emission from this sector is vital. The most commonly used methods for calculating GHG emissions from the livestock sector are life cycle assessment (LCA) and the GHG inventory. Although the LCA presents information on the impacts of the livestock industry on the environment, the GHG inventory is the main tool used internationally for GHG reporting. This review comprehensively discusses the source of GHG emissions from the livestock industry and its estimation methodology, as well as the current strategies for mitigating these emissions.

Implications of seasonal and daily variation on methane and ammonia emissions from naturally ventilated dairy cattle barns in a Mediterranean climate: A two-year study

Seasonal and daily variations of gaseous emissions from naturally ventilated dairy cattle barns are important figures for the establishment of effective and specific mitigation plans. The present study aimed to measure methane (CH4) and ammonia (NH3) emissions in three naturally ventilated dairy cattle barns covering the four seasons for two consecutive years. In each barn, air samples from five indoor locations were drawn by a multipoint sampler to a photoacoustic infrared multigas monitor, along with temperature and relative humidity. Milk production data were also recorded. Results showed seasonal differences for CH4 and NH3 emissions in the three barns with no clear trends within years. Globally, diel CH4 emissions increased in the daytime with high intra-hour variability. The average hourly CH4 emissions (g h-1 livestock unit-1 (LU)) varied from 8.1 to 11.2 and 6.2 to 20.3 in the dairy barn 1, from 10.1 to 31.4 and 10.9 to 22.8 in the dairy barn 2, and from 1.5 to 8.2 and 13.1 to 22.1 in the dairy barn 3, respectively, in years 1 and 2. Diel NH3 emissions highly varied within hours and increased in the daytime. The average hourly NH3 emissions (g h-1 LU-1) varied from 0.78 to 1.56 and 0.50 to 1.38 in the dairy barn 1, from 1.04 to 3.40 and 0.93 to 1.98 in the dairy barn 2, and from 0.66 to 1.32 and 1.67 to 1.73 in the dairy barn 3, respectively, in years 1 and 2. Moreover, the emission factors of CH4 and NH3 were 309.5 and 30.6 (g day-1 LU-1), respectively, for naturally ventilated dairy cattle barns. Overall, this study provided a detailed characterization of seasonal and daily gaseous emissions variations highlighting the need for future longitudinal emission studies and identifying an opportunity to better adequate the existing mitigation strategies according to season and daytime.

Towards climate neutrality in the Spanish N-fertilizer sector: A study based on radiative forcing

Agricultural systems in the 21st Century face the double challenge of achieving climate neutrality while maintaining food security. Synthetic fertilizers rich in nitrogen (N-fertilizers) boost agricultural production at the expense of increasing climate impact. Public policies, such as the Farm-to-Fork (F2F) Strategy, aim to reduce the extensive use of N-fertilizers with the ultimate goal of achieving a climate neutral European Union (EU). However, the strong link between N-fertilizers and GHG emissions (i.e., CO2, CH4 and, especially, N2O) highlights the need to better understand the climate impact of this sector. The present study conducts a climate impact analysis of Spanish N-fertilizer sector for two periods: (i) from 1960 to 2020 using real data and (ii) from 2021 to 2100 considering five forecasted scenarios. The scenarios range from business-as-usual practices to a full accomplishment of the goals pursued by the EU's F2F strategy. The system's climate stability and neutrality are analysed for the different scenarios based on radiative forcing (RF) metrics. Additionally, the study evaluates the short-term impact of the EU decarbonization goals on the climate impact of the Spanish N-fertilizer sector. The results of the study illustrate that the long-lasting climate impact of N2O and CO2 emissions compromise the capacity of N-fertilizer sector to achieve climate stability and approach climate neutrality. However, the decarbonisation of transport and N-fertilizer production activities is an important driver to substantially reduce the life cycle CH4 and CO2 emissions in the Spanish N-fertilizer sector. The results also highlight that more severe reductions on N-cycles than those suggested by the EU's F2F are required, especially to reduce the long-lasting N2O emissions in the N-fertilizer sector. Overall, the study concludes that using RF-based metrics increases robustness and transparency of climate assessments, which is necessary for a higher integration of climate science within public policymaking.

Effect of buffer pH on methane production and fermentation characteristics of three forages tested in vitro

BACKGROUND

Low rumen pH is proposed to be a major mechanism for low methane (CH4) emissions from sheep fed forage rape. However, it is difficult to separate this from other in vivo factors, such as rumen passage rate. The objective of this study was to determine the effect of pH alone on CH4 production in vitro using different pH buffers. Ryegrass, white clover and forage rape were incubated in vitro using three different incubation buffers with starting pH values of 5.5, 6.2 and 6.8.

RESULTS

Decreasing pH reduced overall in vitro CH4 emission relative to fermented hexoses (CH4/FHex) by up to 54% and overall fermentation by 40%. pH also changed fermentation profiles where the acetate + butyrate to propionate + valerate ratio decreased when pH decreased. Within the three forages, forage rape led to the lowest CH4/FHex, but only in pH 5.5 and 6.2 buffer, and this was enhanced when the pH fell below 6.

CONCLUSION

Reducing pH in vitro decreased CH4 production and overall fermentation across all forages. The lower pH reached by forage rape compared to ryegrass and white clover appears to drive the lower CH4 production relative to the extent of fermentation from forage rape compared to the other forages. © 2024 The Author(s). Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Methane emissions and rumen microbiome response during compensatory growth on either a forage or grain-based finishing diet in beef cattle

The aim of this experiment was to evaluate the effect of the level of prior nutritional restriction during backgrounding in Angus steers on methane (CH4) emissions, diet digestibility, rumen fermentation, and ruminal microbiome under either a forage or grain-based finishing diet. Eighty steers (body weight [BW]: 444 ± 39 kg, age: 18 ± 1 mo) were blocked and randomly assigned within the block to either an optimal (0.6 to 0.7 kg/d) or suboptimal (0.3 to 0.4 kg/d) growth rate to exploit compensatory growth (CG), during 97 d of backgrounding. Following, for 84 d, half of the steers in each group were finished on a forage diet while the other half were finished on a grain-based diet. During the backgrounding period, CH4 emissions tended (P ≤ 0.07) to be higher; however, CH4 intensity expressed by BW gain was 50% lower (P < 0.01) for optimal compared to suboptimal growth steers. BW gain, dry matter intake, diet digestibility, and ammonia nitrogen in the rumen were greater (P < 0.01) for optimal compared to suboptimal steers. During the finishing period, CH4 emissions in either forage or grain finishing diets were similar (P > 0.05) for both backgrounding treatments. However, due to greater BW gain in suboptimal steers (1.20 vs. 0.97 kg/d), their CH4 intensity-related coefficient decreased (P < 0.05) during the finishing period. Diet digestibility or any fermentation parameter was unaffected (P > 0.05) by previous backgrounding during the finishing period. In fact, rumen microbial abundance measured during finishing was not modified (P > 0.05) by previous backgrounding. Steers finished under grain conditions, had lower (P < 0.01) daily CH4 emissions and CH4 intensity. Additionally, grain-fed steers increased (P < 0.05) BW gain, diet digestibility, propionic, lactic, and valeric acids, Succinivibrionaceae family and Succiniclasticum, Erysipelotrichaceae UCG-002, Sharpea, and Megasphaera bacteria genera, compared to forage-fed steers. In conclusion, ruminal microbiome and fermentation, diet digestibility, and CH4 emissions were unaffected during finishing between prior levels of backgrounding growth. However, given the higher BW gain in suboptimal steers in both finishing diets, CH4 intensity was reduced in comparison to the optimal backgrounded steers. Nevertheless, lifetime emissions of the steers need to be assessed with the different dietary regimens, since suboptimal steers reduced CH4 emissions during the backgrounding period but, additional days of finishing were required to achieve the same BW as their contemporaries.

Exploring putative enteric methanogenesis inhibitors using molecular simulations and a graph neural network

Atmospheric methane (CH4) acts as a key contributor to global warming. As CH4 is a short-lived climate forcer (12 years atmospheric lifespan), its mitigation represents the most promising means to address climate change in the short term. Enteric CH4 (the biosynthesized CH4 from the rumen of ruminants) represents 5.1% of total global greenhouse gas (GHG) emissions, 23% of emissions from agriculture, and 27.2% of global CH4 emissions. Therefore, it is imperative to investigate methanogenesis inhibitors and their underlying modes of action. We hereby elucidate the detailed biophysical and thermodynamic interplay between anti-methanogenic molecules and cofactor F430 of methyl coenzyme M reductase and interpret the stoichiometric ratios and binding affinities of sixteen inhibitor molecules. We leverage this as prior in a graph neural network to first functionally cluster these sixteen known inhibitors among ~54,000 bovine metabolites. We subsequently demonstrate a protocol to identify precursors to and putative inhibitors for methanogenesis, based on Tanimoto chemical similarity and membrane permeability predictions. This work lays the foundation for computational and de novo design of inhibitor molecules that retain/ reject one or more biochemical properties of known inhibitors discussed in this study.

Energy utilization in lactating Jersey cows consuming a mixture of DDGS and straw replacing alfalfa hay

Some forages require significant amounts of water to grow, causing the dairy industry to be dependent on a limited resource. Feeding crop residues and feed coproducts in dairy rations may represent opportunities when alfalfa is not readily available, and to reduce the industry's use of water. A study using indirect calorimetry and 12 multiparous lactating Jersey cows (BW = 447.5 ± 43.7 kg; DIM = 71 ± 11 d, mean ± SD) was conducted to determine the effect of feeding dried distillers grains and solubles (DDGS) and straw in replacement of alfalfa hay on milk production and energy utilization. A triplicated 4 × 4 Latin square design was used to evaluate the replacement of alfalfa hay with a coproduct mixture (COP) of wheat straw and DDGS. Animals were blocked by milk yield and randomly assigned to 1 of 4 experimental treatments including (proportions on a DM basis): a control diet (CON) containing 18.2% of alfalfa hay, a low-coproduct diet (LCOP) that contained 8.1% of COP, a medium-coproduct diet (MCOP) that contained 16.3% of COP, and a high-coproduct diet (HCOP) that contained 24.3% of COP. No differences were observed for daily dry matter intake or milk yield (mean ± SEM) 19.5 kg ± 0.60, 29.6 kg ± 0.91, respectively. A quadratic tendency was observed where increasing inclusion of COP up to 16.3% maintained ECM and milk fat yield but decreased when animals were fed 24.3% COP. Total methane production decreased linearly from 429.4 to 345.0 ± 22.8 L/d from CON to HCOP diets, respectively. The digestibility of CP increased linearly from 64.0 to 70.4 ± 0.95% and N balance increased linearly from 43.3 to 90.7 ± 15.0 g/d in animals consuming CON to HCOP diets. Total time spent ruminating was lowest in animals consuming the HCOP diet. A linear increasing tendency in digestible and metabolizable energy of 2.92 to 3.02 ± 0.041 Mcal/kg and 2.58 to 2.70 ± 0.047 Mcal/kg was observed in animals consuming CON to HCOP. The proportion ME from DE (ME/DE) tended to linearly increase from 88.3 to 89.4 ± 0.454 when COP was added to the diet. Results of this study indicate that alfalfa hay with a mixture of straw and DDGS can maintain milk production and DMI, but the partial or full replacement of alfalfa with the COP mixture may result in differences in energy utilization in part driven by effects on CH4 reduction.

Phenotypic traits related to methane emissions from Holstein dairy cows challenged by low or high forage proportion

Limited literature is available identifying phenotypical traits related to enteric methane (CH4) production from dairy cows, despite its relevance in relation to breeding for animals with a low CH4 yield (g/kg DMI), and the derived consequences hereof. This study aimed to investigate the relationships between CH4 yield and different animal phenotypes when 16 2nd parity dairy cows, fitted with a ruminal cannula, were fed 2 diets differing in forage:concentrate ratio in a crossover design. The diets had either a low forage proportion (35% on DM basis, F35) or a high forage proportion (63% on DM basis, F63). Gas exchange was measured by means of indirect calorimetry. Spot samples of feces were collected, and indigestible NDF (INDF) was used as an internal marker to determine total-tract digestibility. In addition, ruminal evacuations, monitoring of chewing activity, determination of ruminal VFA concentration, analysis of relative abundance of methanogens, and measurement of liquid passage rate were performed. Statistical differences were analyzed by a linear mixed model with diet, days in milk, and period as fixed effects, and cow as random effect. The random cow estimates (RCE) were extracted from the model to get the Pearson correlations (r) between RCE of CH4 yield with RCE of all other variables measured, to identify possible phenotypes related to CH4 yield. Significant correlations were observed between RCE of CH4 yield and RCE of OM digestibility (r = 0.63) and ruminal concentration of valeric acid (r = -0.61), acetic acid (r = 0.54), ammonium (r = 0.55), and lactic acid (r = ‒0.53). Additionally, tendencies were observed for correlations between RCE of CH4 yield and RCE of H2 yield in g/kg DM (r = 0.47, P = 0.07), and ruminal isobutyric acid concentration (r = 0.43, P = 0.09). No correlations were observed between RCE of CH4 yield and RCE of ruminal pool sizes, milk data, urinary measurements, or chewing activity. Cows had a lower DMI and ECM, when they were fed F63 compared with F35. Cows fed F63 had higher NDF digestibility, CH4 emissions (g/d, g/kg of DMI, and g/kg of ECM), ruminal concentration of acetic acid, ruminal pH, degradation rate of digestible NDF (DNDF, %/h), and longer rumen retention time (h). Also, rumination and total chewing time (min/kg DMI) were higher for cows fed F63. The results in the present study emphasize the positive relation between cow's ability to digest OM and their CH4 emissions. The derived consequences of breeding for lower CH4 emission might be cows with lower ability to digest OM, but more studies are warranted for further documentation of this relationship.

Greenhouse gas emissions in US beef production can be reduced by up to 30% with the adoption of selected mitigation measures

Greenhouse gas (GHG) emissions from beef production in the United States are unevenly distributed across the supply chain and production regions, complicating where and how to reduce emissions most effectively. Using spatially explicit life cycle assessment methods, we quantify the baseline GHG emissions and mitigation opportunities of 42 practices spanning the supply chain from crop and livestock production to processing. We find that the potential to reduce GHGs across the beef sector ranges up to 30% (20 million tonnes CO2e reduced and 58 million tonnes CO2 sequestered each year relative to the baseline) under ubiquitous adoption assumptions, largely driven by opportunities in the grazing stage. Opportunities to reduce GHGs in the feed, grazing and feedlot stages vary across regions, yet large-scale adoption across the entire beef supply chain is important. These findings reveal promising locations and practices to invest in to advance mitigation goals and an upper-end theoretical potential for mitigation in the beef industry.

Effects of 3-nitrooxypropanol (Bovaer10) and whole cottonseed on milk production and enteric methane emissions from dairy cows under Swiss management conditions

The objective of this study was to determine the potential effect and interaction of 3-nitrooxypropanol (3-NOP; Bovaer, DSM-Firmenich Nutrition Products Ltd.) and whole cottonseed (WCS) on lactational performance and enteric methane (CH4) emission of dairy cows. A total of 16 multiparous cows, including 8 Holstein Friesian (HF) and 8 Brown Swiss (BS; 224 ± 36 DIM, 26 ± 3.7 kg milk yield, mean ± SD), were used in a split-plot design, where the main plot was the breed of cows. Within each subplot, cows were randomly assigned to a treatment sequence in a replicated 4 × 4 Latin square design with 2 × 2 factorial arrangements of treatments with four 24-d periods. The experimental treatments were as follows: (1) control (basal TMR), (2) 3-NOP (60 mg/kg TMR DM), (3) WCS (5% TMR DM), and (4) 3-NOP + WCS. The treatment diets were balanced for ether extract, crude protein, and NDF contents (4%, 16%, and 43% of TMR DM, respectively). The basal diets were fed twice daily at 0800 and 1800 h. Dry matter intake and milk yield were measured daily, and enteric gas emissions were measured (using the GreenFeed System, C-Lock Inc.) during the last 3 d of each 24-d experimental period when animals were housed in tiestalls. There was no difference in DMI on treatment level, whereas the WCS treatment increased ECM yield and milk fat yield. No interaction of 3-NOP and WCS occurred for any of the enteric gas emission parameters, but 3-NOP decreased CH4 production (g/d), CH4 yield (g/kg DMI), and CH4 intensity (g/kg ECM) by 13%, 14%, and 13%, respectively. Further, an unexpected interaction of breed by 3-NOP was observed for different enteric CH4 emission metrics: HF cows had a greater CH4 mitigation effect compared with BS cows for CH4 production (g/d; 18% vs. 8%), CH4 intensity (g/kg milk yield; 19% vs. 3%), and CH4 intensity (g/kg ECM; 19% vs. 4%). Hydrogen production was increased by 2.85-fold in HF and 1.53-fold in BS cows receiving 3-NOP. Further, a 3-NOP × time interaction occurred for both breeds. In BS cows, 3-NOP tended to reduce CH4 production by 18% at approximately 4 h after morning feeding, but no effect was observed at other time points. In HF cows, the greatest mitigation effect of 3-NOP (29.6%) was observed immediately after morning feeding, and it persisted at around 23% to 26% for 10 h until the second feed provision, and 3 h thereafter, in the evening. In conclusion, supplementing 3-NOP at 60 mg/kg DM to a high-fiber diet resulted in 18% to 19% reduction in enteric CH4 emission in Swiss HF cows. The lower response to 3-NOP by BS cows was unexpected and has not been observed in other studies. These results should be interpreted with caution due to the low number of cows per breed. Finally, supplementing WCS at 5% of DM improved ECM and milk fat yield but did not enhance the CH4 inhibition effect of 3-NOP of dairy cows.

Ruminal microbiome changes across lactation in primiparous Holstein cows with varying methane intensity: Heritability assessment

Methane is a potent greenhouse gas produced during the ruminal fermentation and is associated with a loss of feed energy. Therefore, efforts to reduce methane emissions have been ongoing in the last decades. Methane production is highly influenced by factors such as the ruminal microbiome and host genetics. Previous studies have proposed to use the ruminal microbiome to reduce long-term methane emissions, as ruminal microbiome composition is a moderately heritable trait and genetic improvement accumulates over time. Lactation stage is another important factor that might influence methane production, but potential associations with the ruminal microbiome have not been evaluated previously. This study sought to examine the changes in ruminal microbiome over the lactation period of primiparous Holstein cows differing in methane intensity (MI) and estimate the heritability of the abundance of relevant microorganisms. Ruminal content samples from 349 primiparous Holstein cows with 14 to 378 DIM were collected from May 2018 to June 2019. Methane intensity of each cow was calculated as methane concentration/milk yield. Up to 64 taxonomic features (TF) from 20 phyla had a significant differential abundance between cows with low and high MI early in lactation, 16 TF during mid lactation, and none late in lactation. Taxonomical features within the Firmicutes, Proteobacteria, Melainabacteria, Cyanobacteria, Bacteroidetes, and Actinobacteria phyla were associated with low MI, whereas eukaryotic TF and those within the Euryarchaeota, Verrucomicrobia, Kiritimatiellaeota, and Lentisphaerae phyla were associated with high MI. Out of the 60 TF that were found to be differentially abundant between early and late lactation in cows with low MI, 56 TF were also significant when cows with low and high MI were compared in the first third of the lactation. In general, microbes associated with low MI were more abundant early in lactation (e.g., Acidaminococcus, Aeromonas, and Weimeria genera) and showed low to moderate heritabilities (0.03 to 0.33). These results suggest some potential to modulate the rumen microbiome composition through selective breeding for lower MI. Differences in the ruminal microbiome of cows with extreme MI levels likely result from variations in the ruminal physiology of these cows and were more noticeable early in lactation, probably due to important interactions between the host phenotype and environmental factors associated with that period. Our results suggest that the ruminal microbiome evaluated early in lactation may be more precise for MI difference, and hence, this should be considered to optimize sampling periods to establish a reference population in genomic selection scenarios.

Review: Improving residual feed intake modelling in the context of nutritional- and genetic studies for dairy cattle

The residual feed intake (RFI) model has recently gained popularity for ranking dairy cows for feed efficiency. The RFI model ranks the cows based on their expected feed intake compared to the observed feed intake, where a negative phenotype (eating less than expected) is favourable. Yet interpreting the biological implications of the regression coefficients derived from RFI models has proven challenging. In addition, multitrait modelling of RFI has been proposed as an alternative to the least square RFI in nutrition and genetic studies. To solve the challenge with the biological interpretation of RFI regression coefficients and suggest ways to improve the modelling of RFI, an interdisciplinary effort was required between nutritionists and geneticists. Therefore, this paper aimed to explore the challenges with the traditional least square RFI model and propose solutions to improve the modelling of RFI. In the traditional least square RFI model, one set of fixed effects is used to solve systematic effects (e.g., seasonal effects and age at calving) for traits with different means and variances. Thereby, measurement and model fitting errors can accumulate in the phenotype, resulting in undesirable effects. A multivariate RFI model will likely reduce this problem, as trait-specific fixed effects are used. In addition, regression coefficients for DM intake on milk energy tend to have more biologically meaningful estimates in multitrait RFI models, which indicates a confounding effect between the fixed effects and regression coefficients in the least square RFI model. However, defining precise expectations for regression coefficients from RFI models or sourcing for accurate feed norm coefficients seems difficult, especially if the coefficients are applied to a wide cattle population with varying diets or management systems, for example. To improve multitrait modelling of RFI, we suggest improving the modelling of changes in energy status. Furthermore, a novel method to derive the energy density of the diet and individual digestive efficiency is proposed. Digestive efficiency is defined as the part of the efficiency associated with digestive processes, which primarily reflects the conversion from gross energy to metabolisable energy. We show the model was insensitive to prior values of energy density in feed and that there was individual variation in digestive efficiency. The proposed method needs further development and validation. In summary, using multitrait RFI can improve the accuracy of the ranking of dairy cows' feed efficiency, consequently improving economic and environmental sustainability on dairy farms.

Ruminal methane emission and lactational performance of cows fed rapeseed cake and oats on a grass silage-based diet

The objective of this experiment was to investigate the effect of lipid from rapeseed cake and oats on ruminal CH4 emission and lactational performance of dairy cows. Twelve lactating Nordic Red cows, of which 4 were primiparous, and averaging (±SD) 48 ± 22.9 DIM, 37.8 ± 7.14 kg/d milk yield were enrolled in a switch-back design experiment with 3 periods of 4 wk each. The cows were assigned into 6 pairs based on parity, DIM, milk yield, and BW at the beginning of the experiment. The experimental treatments were (1) rapeseed cake and oats (RSC+O), and (2) rapeseed meal and barley (RSM+B) as the concentrate feeds. Cows in each pair were randomly assigned to 1 of the 2 groups, which received the treatments in 2 different sequences (i.e., group 1 received RSC+O in period 1 and 3, and RSM+B in period 2, whereas group 2 was fed RSM+B in period 1 and 3, and RSC+O in period 2). The diets consisted of a partially mixed ration with grass silage mixed with either oats or barley, according to the treatment sequence, and the rapeseed cake or meal being mixed into a pellet with either oats or barley according to the treatments, and a mineral mix. The pellet was delivered at a fixed amount (i.e., 6 kg/d for multiparous and 5 kg/d for the primiparous cows) from the milking robot. The actual forage to concentrate ratios for RSC+O and RSM+B were 51:49 and 52:48, respectively, with NDF concentrations of 41.5% and 36.0% and CP concentrations of 17.0% and 16.7% of diet DM. Dry matter intake, milk yield, and gas exchange (with a GreenFeed system attached to the milking robot) were recorded daily, and milk composition and spot fecal samples were collected during the last week of each period. Based on feed analysis, and DMI of the cows during the experiment, the total fat content of the experimental diets was 4.1% and 2.7% of DM for RSC+O and RSM+B diets, respectively. Dry matter intake was 1.6 kg/d lower, and milk yield tended to be 1.0 kg/d greater for RSC+O versus RSM+B. There were no differences in ECM yield and milk composition between the treatments, whereas milk ME efficiency was greater for cows fed RSC+O than RSM+B. Methane yield (g/kg DMI) did not differ between treatments, but CH4 production (g/d) was 9.4% and CH4 intensity as g/kg ECM was 11.7% lower for RSC+O versus RSM+B. The lower CH4 production was likely caused by the lower DMI and fiber digestibility, observed with the RSC+O diet. In addition, the greater lipid intake also contributed to lower rate of fermentation and subsequent decrease in CH4 production. Overall, feeding rapeseed cake with oats in a grass silage-based diet increased feed efficiency while decreasing CH4 emission intensity in lactating cows. This provides a practical way of mitigating ruminal CH4 emission from dairy operations while maintaining milk production with commonly used feedstuffs in Nordic conditions.

Editing microbes to mitigate enteric methane emissions in livestock

Livestock production significantly contributes to greenhouse gas (GHG) emissions particularly methane (CH4) emissions thereby influencing climate change. To address this issue further, it is crucial to establish strategies that simultaneously increase ruminant productivity while minimizing GHG emissions, particularly from cattle, sheep, and goats. Recent advancements have revealed the potential for modulating the rumen microbial ecosystem through genetic selection to reduce methane (CH4) production, and by microbial genome editing including CRISPR/Cas9, TALENs (Transcription Activator-Like Effector Nucleases), ZFNs (Zinc Finger Nucleases), RNA interference (RNAi), Pime editing, Base editing and double-stranded break-free (DSB-free). These technologies enable precise genetic modifications, offering opportunities to enhance traits that reduce environmental impact and optimize metabolic pathways. Additionally, various nutrition-related measures have shown promise in mitigating methane emissions to varying extents. This review aims to present a future-oriented viewpoint on reducing methane emissions from ruminants by leveraging CRISPR/Cas9 technology to engineer the microbial consortia within the rumen. The ultimate objective is to develop sustainable livestock production methods that effectively decrease methane emissions, while maintaining animal health and productivity.