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

Changes in the Rumen Microbiota of Cows in Response to Dietary Supplementation with Nitrate, Linseed, and Saponin Alone or in Combination

Dietary supplementation with linseed, saponins, and nitrate is a promising methane mitigation strategy in ruminant production. Here, we aimed to assess the effects of these additives on the rumen microbiota in order to understand underlying microbial mechanisms of methane abatement. Two 2-by-2 factorial design studies were conducted simultaneously, which also allowed us to make a broad-based assessment of microbial responses. Eight nonlactating cows were fed diets supplemented with linseed or saponin in order to decrease hydrogen production and nitrate to affect hydrogen consumption; also, combinations of linseed plus nitrate or saponin plus nitrate were used to explore the interaction between dietary treatments. Previous work assessed effects on methane and fermentation patterns. Rumen microbes were studied by sequencing 18S and 16S rRNA genes and ITS1 amplicons. Methanogen activity was monitored by following changes in mcrA transcript abundance. Nitrate fed alone or in combination in both studies dramatically affected the composition and structure of rumen microbiota, although impacts were more evident in one of the studies. Linseed moderately modified only bacterial community structure. Indicator operational taxonomic unit (OTU) analysis revealed that both linseed and nitrate reduced the relative abundance of hydrogen-producing Ruminococcaceae Linseed increased the proportion of bacteria known to reduce succinate to propionate, whereas nitrate supplementation increased nitrate-reducing bacteria and decreased the metabolic activity of rumen methanogens. Saponins had no effect on the microbiota. Inconsistency found between the two studies with nitrate supplementation could be explained by changes in microbial ecosystem functioning rather than changes in microbial community structure.IMPORTANCE This study aimed at identifying the microbial mechanisms of enteric methane mitigation when linseed, nitrate, and saponins were fed to nonlactating cows alone or in a combination. Hydrogen is a limiting factor in rumen methanogenesis. We hypothesized that linseed and saponins would affect hydrogen producers and nitrate would affect hydrogen consumption, leading to reduced methane production in the rumen. Contrary to what was predicted, both linseed and nitrate had a deleterious effect on hydrogen producers; linseed also redirected hydrogen consumption toward propionate production, whereas nitrate stimulated the growth of nitrate-reducing and, hence, hydrogen-consuming bacterial taxa. This novel knowledge of microbial mechanisms involved in rumen methanogenesis provides insights for the development and optimization of methane mitigation strategies.

Environmental efficiency of Saccharomyces cerevisiae on methane production in dairy and beef cattle via a meta-analysis

The objective of the present study is to examine the effect of yeast (Saccharomyces cerevisiae) on reduction of methane (CH₄) production in dairy and beef cattle using meta-analytic methods. After compilation of relevant scientific publications available from the literature between 1990 and 2016, and applying exclusion and inclusion criteria, meta-analyses of data from dairy and beef cattle were applied for the pooled dataset or for each animal category (dairy or beef). The results of meta-analysis of all three datasets (all cattle, dairy cattle, or beef cattle) suggested that effect size of yeast either on daily CH₄ production or on CH₄ production per dry matter intake (CH₄/DMI) was not significant. The results of Q test and I² statistic suggest that there is no heterogeneity between different studies on CH₄ production and CH₄/DMI. The results of meta-analysis suggest that use of yeast (Saccharomyces cerevisiae) as feed additive does not offer significant results in terms of reduction of CH₄ production in dairy and beef cattle. Further research on the effects of different doses of yeast, use of yeast products, different strains, and experimental designs is warranted to elucidate the effects of yeasts on methane production in the rumen.

Effect of supplementation of saponin containing herbs on in vitro methane production under different feeding systems

This study was taken up to assess the effect of herbal feed additives [HFAs; kulthi (Dohichos biflorus), patha (Cissampelos pareria), aritha (Sapindus trifoliatus)] supplemented at 0–3% on DM basis of total mixed rations (TMR) on the in vitro methane production and nutrient fermentation in a 3 × 4 factorial design. TMR with different roughage to concentrate ratio (R:C) of 80:20, 75:25, 70:30 and 65:35 on DM basis were formulated. The roughage portion was made up of wheat straw and maize green fodder in 70:30 ratio. The chemical analysis of HFAs revealed that aritha had the highest concentration of both water and methanol soluble saponins; and condensed tannins (Leucocyanidin). Patha followed by kulthi had the highest concentration of vitamin C, flavonoids, total phenols and true tannins. The digestion kinetic parameters revealed that with the increase in level of concentrate in the diet, irrespective of type and level of supplementation of HFAs, the lag phase for fermentation of diet decreased linearly. The data conclusively revealed that the best response with respect to net gas production (NGP), digestibility of nutrients, methane production, volatile fatty acid (VFA) production, ME availability and other fermentation parameters from TMRs with different R:C ratios was observed in kulthi and patha supplemented at the rate of 2% of TMR with R:C ratio of 65:35 on DM basis.

Quantification of methane emissions from Murrah buffaloes fed different energy diets during various temperature humidity index periods in a tropical environment

The objective of the present study was to quantify the enteric methane emission in Murrah buffalo heifers at high (summer) and low (winter) temperature humidity index (THI) period fed different energy level diets. Thirty-six growing Murrah buffalo heifers of average bodyweight (158.51 ± 16.5 kg) were distributed into three groups of six animals each separated based on their bodyweight and fed for the period of 120 days each during summer (high THI, 78–85) and winter (low THI, 50–61). The animals were fed on three different levels of metabolisable energy (ME) content and the Control ration (T1) having ME content according to ICAR (2013) and T2 and T3 were having 115% and 85% ME than the Control respectively, in total mixed-based ration. The SF6 tracer gas technique was used to quantify the enteric methane emission by the animals. Methane emission (g/day) of Control and the high energy (T1 and T2) group was lower (P < 0.05) than the low energy (T3) fed group in both seasons. Methane losses as percentage of gross energy intake was lower (P < 0.01) during the winter season. However, in the low energy treatment group (T3) at both seasons these values are higher than the IPCC recommended value (6.5%) for calculation of national inventory of greenhouse gas emission from enteric sources. In between season average daily gain (kg) was higher (P < 0.01) in the winter season and among the treatment groups it was higher (P < 0.01) in the high energy group (T1, T2). Higher (P < 0.01) digestibility of dry matter, organic matter, neutral detergent fibre and acid detergent fibre was reported in the Control and high energy-fed group. Whereas in the summer season digestibility of dry matter, organic matter, crude protein and acid detergent fibre was higher (P < 0.01) than in the winter season. It can be concluded that energy levels significantly (P < 0.05) affect methane emissions and was lower in the Control and high energy-fed group (T1 and T2). However, while quantifying methane emission in changing THI period at different seasons it did not show any significant variation.

Health and nutrition in sheep receiving Bacillus thuringiensis

Performance, nutrient apparent digestibility, ruminal parameters, enteric methane (CH4) emission and blood parameters were studied in sheep receiving spores of Bacillus thuringiensis (Bt) in their diet. Twenty Santa Inês lambs (10 castrated males and 10 females) with 18.0 ± 3.50 kg initial bodyweight (BW) and 3 months of age were maintained in individual stalls in a completely randomised design. They were divided into two groups with five males and five females each (Bt 2036 group (n = 10) and control group (n = 10)). The animals of the Bt 2036 group received daily 2.5 × 106 spores of Bt 2036/kg BW and control animals received a placebo. The diet consisted of Tifton-85 (Cynodon spp.) hay ad libitum and 300 g/animal.day of concentrate mixture, which was adjusted according to growth requirements. During 53 days, animal performance was evaluated, with feed intake measured three times per week and lambs weighed fortnightly. Blood samples were taken every 15 days to evaluate hematological and biochemical parameters. Rumen fermentation was investigated in three stages (start, middle and end of the experimental period) using parameters such as pH, ammoniacal nitrogen, short chain fatty acids, and populations of Fibrobacter succinogenes, Ruminococcus flavefaciens, anaerobic fungi, methanogenic archaea and protozoa. At the end of the performance experiment, 18 lambs (Bt 2036 (n = 9), control (n = 9)) were selected for a digestibility trial, and placed in metabolic cages to estimate apparent nutrient digestibility, nitrogen balance and microbial protein synthesis. Ten male (Bt 2036 (n = 5), control (n = 5)) lambs were used to evaluate CH4 production using the hexafluoride tracer technique. There was no effect (P > 0.05) of Bt 2036 on any of the evaluated parameters. The daily addition of 2.5 × 106 spores/kg BW of Bt 2036 in the ruminant diet did not cause any negative effects on hematological traits or animal poisoning, nor did it interfere with fermentation by rumen microorganisms, apparent digestibility of nutrients or animal performance.

Methane emissions from Nellore bulls on pasture fed two levels of starch-based supplement with or without a source of oil

Methane emissions (CH4) from enteric fermentation represent an energy loss to the animal ranging from 2% to 12% of gross energy (GE) intake; therefore, the challenge is to develop diets and handling strategies to mitigate CH4 emissions. This study tested the hypothesis that fat supplementation as a source of energy could reduce CH4 emissions without decrease animal production, independently of the starch level utilised. Thus, the goal of this study was to assess the combined effects of high- or low-starch supplements with or without a source of oil (soybean grain) on intake, digestibility, performance, and CH4 emissions of finishing Nellore bulls [n = 44; initial bodyweight (BW) = 414 ± 12 kg; age of 20 months] grazing on Brachiaria brizantha cv. Xaraés during the dry season. No interactions between starch level and oil source (soybean grain) supplementation with respect to intake of dry matter (DM), forage DM, supplement DM, organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), ether extract (EE), or GE were found. However, there was an effect of starch and oil source on intake of EE. There were no interactions between starch level and oil source supplementation with respect to digestibility of DM, OM, NDF, CP, EE, or digestibility energy. Irrespective of the starch level utilised, the addition of soybean grain (oil source) decreased the digestibility of NDF and increased the digestibility of EE. In relation to animal performance, there were no interactions between starch level and oil regarding initial BW, final BW, average daily gain (ADG), gain efficiency, hot carcass weight, dressing, carcass gain, fat depth, or longissimus muscle area. However, the addition of soybean grain (oil source) increased the fat depth independently of the starch level used. There was no interaction between starch-based supplementation level and oil source on CH4 emissions when expressed in g/day, g/kg DM intake, g/kg OM intake, g/kg NDF intake, % of GE intake, g/g EE intake, g/kg ADG, or g/kg of carcass gain. Therefore, the addition of soybean grain (oil source) in supplements, independent of starch level used, was associated with reduced CH4 emissions expressed in g/day. Additionally, soybean grain (oil source) decreased enteric CH4 emissions relative to GE and EE intake and ADG for animals fed high- or low-starch supplements. Soybean grain supplementation is effective at reducing enteric CH4 emissions from Nellore bulls grazing on tropical pasture.

Estimation and mitigation of GHG emissions from ruminant livestock in Pakistan

The study examined baseline emissions of greenhouse gases from ruminant livestock in Pakistan for the year 2014 and evaluated feasible interventions for mitigating the sector emissions. Total emissions (as CO2-equivalents) from livestock supply chain from cradle to farm gate were estimated at 431007 × 103 t. Major part (77%) of the emissions was produced by the mixed system and the remaining 23% was contributed by the grazing system. Methane emissions were 62.5% of the total emissions, followed by N2O at 29.4% and CO2 at 8.1%. Bulk of milk (87.6%) and meat (59.4%) was produced by the mixed system, which was associated with three-fold higher emissions at 332248 × 103 t than when they were produced by the grazing system. The emission intensity (kg CO2-eq/kg protein) of milk and meat averaged 183.4 and 443.2 respectively, and ranked higher than the global average values. Buffaloes were responsible for the major proportion of emissions, followed by cattle. Average emissions per animal in buffalo, cattle, sheep and goat were 4.27, 3.27, 0.28 and 0.25 t CO2-eq/year respectively. The emission intensities (kg CO2-eq/kg commodity protein) of both milk and meat remained lower in cattle than buffalo and were calculated as 166.1 and 299.7 in cattle and 189.5 and 527.9 in buffaloes respectively. The carbon footprint of milk and meat in sheep and goats also remained high and averaged 189.0 and 472.6 kg CO2-eq/kg protein respectively. Overall, the emission intensity of meat was slightly higher in the grazing system than mixed system, but remained much higher in non-dairy herds than in dairy herds (1006.6 vs 46.6 kg CO2-eq/kg meat protein). Interventions such as improving diet quality through increased fodder supply, vaccination for adequate health control and genetic improvement reduced emission intensities of milk (kg CO2-eq/kg protein), varying from 20.3% to 36.8% compared with the baseline in dairy cows and buffaloes and this was associated with a positive productivity outcome of enhanced milk production by 25–50%. More significant reduction in emission intensities of milk between 48.1% and 53.1%, together with a 100% increase in milk yield above baseline, resulted from combined application of the three interventions as a single package.

Methanogenesis in animals with foregut and hindgut fermentation: a review

Methane is the main greenhouse-gas contributor to global warming in the livestock sector; it is generated by anaerobic fermentation in the different sections of the gut, and the methane concentration differs significantly among species. Methane is produced only by certain types of microorganisms called methanogens. The species composition of methanogenic archaea population is largely affected by the diet, geographical location, host and the section of the gut. Consequently, methane production, either measured as total grams emitted per day or per bodyweight mass, differs greatly among animal species. The main difference in methanogenic activity among different gut sections and animal species is the substrate fermented and the metabolic pathway to complete anaerobic fermentation of plant material. The three main substrates used by methanogens are CO2, acetate and compounds containing methyl groups. The three dominant orders of methanogens in gut environments are Methanomicrobiales, Methanobacteriales and Methanosarcinales. They normally are present in low numbers (below 3% of total microbiome). The present review will describe the main metabolic pathways and methanogens involved in CH4 production in the gut of different host-animal species, as well as discuss general trends that influence such emissions, such as geographical distribution, feed composition, section of the gut, host age and diurnal and season variation. Finally, the review will describe animal species (large and small domestic ruminants, wild ruminants, camelids, pigs, rabbits, horses, macropods, termites and humans) specificities in the methanogen diversity and their effects on methane emission.

The effect of silage type on animal performance, energy utilisation and enteric methane emission in lactating dairy cows

The present study aimed to investigate the effect of silage type on dry matter (DM) intake, nutrient digestibility, energy utilisation and methane (CH4) emission. Six late lactating Holstein dairy cows were used in a replicated 3 × 3 Latin square design study with three treatments (grass silage (GS), maize silage (MS) and whole-crop wheat silage (WCWS)) and three periods (3 weeks/period). All animals were offered forage ad libitum and 5.55 kg/day of a concentrate supplement, which contained (DM basis) 66.0% rapeseed meal, 28.3% soyabean meal and 5.7% a mineral/vitamin supplement. During each period, animals were subject to digestibility, CH4 and heat production measurements during the final 6 days using calorimeter chambers. The results demonstrated that total DM intake for MS and WCWS diets were higher (P < 0.001) than for the GS diet. Faecal energy and heat production loss for the GS diet were lower (P < 0.01) than for MS and WCWS diets. In contrast, cows fed the GS diet had higher (P < 0.05) urine energy loss compared with MS and WCWS diets. In comparison with the GS and MS diets, WCWS diet produced a lower CH4 loss per kg DM and organic matter intake (P < 0.01), and CH4 energy output as a proportion of gross energy and metabolisable energy intake (P < 0.05). The present study demonstrates that choice of forage types affects energy utilisation and CH4 emission in dairy cows.

Effect of substituting soybean meal with euglena (Euglena gracilis) on methane emission and nitrogen efficiency in sheep

This study evaluated methane (CH4 ) emission, intake, digestibility, and nitrogen efficiency in sheep fed diets containing replacement levels (0%, 33%, 50%, and 67% of soybean meal with euglena). In this experiment, four Corriedale wether sheep with an initial body weight of 53.8 ± 4.6 were arranged in a 4 × 4 Latin square design. This experiment lasted 84 days, divided into four experimental periods. Each period lasted 21 days, which consists of 14 days of adaptation to the diets, 5 days to collect samples, and 2 days to collect gas emission from sheep. Methane emission expressed as L/kg DM intake or g/kg DM intake reduced by up to 37% and the energy loss via CH4 (% of GE intake) reduced by up to 34%. No differences (p > 0.05) were observed in DM and OM intake and whole tract apparent DM digestibility due to substitution of soybean meal with euglena. The total CP loss reduced significantly (linear, p < 0.001) and CP efficiency increased linearly (p = 0.03) with increasing concentration of euglena. As a result, nitrogen balance and average daily weight gain remained unchanged despite higher nitrogen concentration in soybean supplemented group. In conclusion, substitution of soybean meal with euglena reduced methane emission without affecting the performance of animals.

Effects of eucalyptus oil and anise oil supplementation on rumen fermentation characteristics, methane emission, and digestibility in sheep

The objective of this study was to evaluate antimethanogenic activity of eucalyptus oil (EUC) and anise oil (ANI) in vitro and in vivo using sheep as a model. In vitro study was conducted using batch culture technique, each of EUC and ANI were added at 0, 50, 100, 200, or 400 mg/L of fermentation media with substrate containing 60% corn-based concentrate and 40% hay (DM basis). Total gas production (GP) linearly (P < 0.01) decreased with increasing ANI, whereas the GP was not affected with EUC addition. Supplementation of ANI and EUC linearly (P < 0.01) decreased total methane production and methane proportion in total gas. Total VFA and ammonia-nitrogen (NH3-N) concentration linearly (P < 0.01) decreased with increasing ANI supplementation. For the in vivo study, a replicated 3 × 3 Latin square design was carried out using six ruminal cannulated Du Han hybrid sheep (BW, 64.5 ± 8.56 kg) with 22 d of periods. Three treatments were control diet (consisted of 60% corn-based concentrate and 40% Chinese wildrye hay), EUC (control diet supplemented with 0.5 g EUC/d per head), and ANI (control diet supplemented with 0.5 g ANI/d per head). Each period consisted of 14 d for adaption and 8 d for sampling and data collection. Supplementation of EUC and ANI had no effects on feed intake and apparent nutrient digestibility. Ruminal NH3-N concentration was greater with EUC (P < 0.01) and ANI (P = 0.03) than control. Urinal allantoin output was less (P < 0.05) in sheep fed EUC and ANI than control animals. Methane emission was less (P = 0.03) in sheep fed ANI than sheep fed EUC, and a tendency of decrease for an eduction in this parameter was found for sheep fed with ANI (P = 0.08) compared to control. The in vitro results indicated a reduction of methane production with both EUC and ANI but in a dose-dependant manner. Supplementation of ANI tended to reduce ruminal methane production without adversely affecting rumen fermentation characteristics, nutrient intake, and digestibility, suggesting potential inhibition of ruminal methane emission in sheep supplemented with ANI.

Climate Change and Goat Production: Enteric Methane Emission and Its Mitigation

Simple Summary

Given that goats are considered more climate resilient than other ruminant species, research efforts are therefore needed to understand goat productivity during exposure to high ambient temperatures. Heat stress can affect the digestion and rumen fermentation pattern of goats, which contributes to the reduction in production performance in goats. Diet composition, breed and environmental stresses are common factors which negatively influence rumen function and enteric methane (CH₄) emission. There are three mechanisms by which enteric CH₄ can be reduced: targeting end product of digestion to propionate, providing alternate hydrogen sink and selectively inactivating rumen methanogens. The various strategies that can be implemented to mitigate enteric CH₄ include nutritional interventions, management strategies and application of advanced biotechnological tools.

Abstract

The ability of an animal to cope and adapt itself to the changing climate virtually depends on the function of rumen and rumen inhabitants such as bacteria, protozoa, fungi, virus and archaea. Elevated ambient temperature during the summer months can have a significant influence on the basic physiology of the rumen, thereby affecting the nutritional status of the animals. Rumen volatile fatty acid (VFA) production decreases under conditions of extreme heat. Growing recent evidence suggests there are genetic variations among breeds of goats in the impact of heat stress on rumen fermentation pattern and VFA production. Most of the effects of heat stress on rumen fermentation and enteric methane (CH₄) emission are attributed to differences in the rumen microbial population. Heat stress-induced rumen function impairment is mainly associated with an increase in Streptococcus genus bacteria and with a decrease in the bacteria of Fibrobactor genus. Apart from its major role in global warming and greenhouse effect, enteric CH₄ is also considered as a dietary energy loss in goats. These effects warrant mitigating against CH₄ production to ensure optimum economic return from goat farming as well as to reduce the impact on global warming as CH₄ is one of the more potent greenhouse gases (GHG). The various strategies that can be implemented to mitigate enteric CH₄ emission include nutritional interventions, different management strategies and applying advanced biotechnological tools to find solution to reduce CH₄ production. Through these advanced technologies, it is possible to identify genetically superior animals with less CH₄ production per unit feed intake. These efforts can help the farming community to sustain goat production in the changing climate scenario.

Greenhouse Gas Emissions from Beef Grazing Systems in Semi-Arid Rangelands of Central Argentina

The livestock sector can be a major contributor to the mitigation of greenhouse gas (GHG) emissions. Within the sector, beef production produces the largest proportion of the livestock sector’s direct emissions. The objective of this study was to assess the on-farm GHG emissions in semi-arid rangelands in Argentina and to identify the relationship between emissions and current farm management practices. A survey recorded detailed information on farm management and characteristics. Assessments of GHG emissions were based on the Intergovernmental Panel on Climate Change (IPCC) Tier 2 protocols. The relationship between farm management and GHG emissions were identified using general linear models. Cluster analysis was used to identify groups of farms that differed from others in emissions and farm characteristics. Emissions per product sold were low on farms that had improved livestock care management, rotational grazing, received technical advice, and had high animal and land productivities. Emissions per hectare of farmland were low on farms that had low stocking rates, a low number of grazing paddocks, little or no land dedicated to improved pastures and forage crops, and low land productivity. Our results suggest that the implementation of realistic, relatively easy-to-adopt farming management practices has considerable potential for mitigating the GHG emissions in the semi-arid rangelands of central Argentina.

Validation of mobile in situ measurements of dairy husbandry emissions by fusion of airborne/surface remote sensing with seasonal context from the Chino Dairy Complex

Mobile in situ concentration and meteorology data were collected for the Chino Dairy Complex in the Los Angeles Basin by AMOG (AutoMObile trace Gas) Surveyor on 25 June 2015 to characterize husbandry emissions in the near and far field in convoy mode with MISTIR (Mobile Infrared Sensor for Tactical Incident Response), a mobile upwards-looking, column remote sensing spectrometer. MISTIR reference flux validated AMOG plume inversions at different information levels including multiple gases, GoogleEarth imagery, and airborne trace gas remote sensing data. Long-term (9-yr.) Infrared Atmospheric Sounding Interferometer satellite data provided spatial and trace gas temporal context. For the Chino dairies, MISTIR-AMOG ammonia (NH₃) agreement was within 5% (15.7 versus 14.9 Gg yr^-1, respectively) using all information. Methane (CH₄) emissions were 30 Gg yr^-1 for a 45,200 herd size, indicating that Chino emission factors are greater than previously reported. Single dairy inversions were much less successful. AMOG-MISTIR agreement was 57% due to wind heterogeneity from downwind structures in these near-field measurements and emissions unsteadiness. AMOG CH₄, NH₃, and CO₂ emissions were 91, 209, and 8200 Mg yr^-1, implying 2480, 1870, and 1720 head using published emission factors. Plumes fingerprinting identified likely sources including manure storage, cowsheds, and a structure with likely natural gas combustion. NH₃ downwind of Chino showed a seasonal variation of a factor of ten, three times larger than literature suggests. Chino husbandry practices and trends in herd size and production were reviewed and unlikely to add seasonality. Higher emission seasonality was proposed as legacy soil emissions, the results of a century of husbandry, supported by airborne remote sensing data showing widespread emissions from neighborhoods that were dairies 15 years prior, and AMOG and MISTIR observations. Seasonal variations provide insights into the implications of global climate change and must be considered when comparing surveys from different seasons.

Equine Contribution in Methane Emission and Its Mitigation Strategies

Greenhouses gas emission mitigation is a very important aspect of earth sustainability with greenhouse gasses reduction, a focus of agricultural and petrochemical industries. Methane is produced in nonruminant herbivores such as horses because they undergo hindgut fermentation. Although equine produce less methane than ruminant, increasing population of horses might increase their contribution to the present 1.2 to 1.7 Tg, estimate. Diet, feeding frequency, season, genome, and protozoa population influence methane production equine. In population, Methanomicrobiales, Methanosarcinales, Methanobacteriales, and Methanoplasmatales are the clade identified in equine. Methanocorpusculum labreanum is common among hindgut fermenters like horses and termite. Naturally, acetogenesis and interrelationship between the host and the immune-anatomical interaction are responsible for the reduced methane output in horses. However, to reduce methane output in equine, and increase energy derived from feed intake, the use of biochar, increase in acetogens, inclusion of fibre enzymes and plant extract, and recycling of fecal energy through anaerobic gas fermentation. These might be feasible ways to reducing methane contribution from horse and could be applied to ruminants too.

A parsimonious software sensor for estimating the individual dynamic pattern of methane emissions from cattle

Large efforts have been deployed in developing methods to estimate methane emissions from cattle. For large scale applications, accurate and inexpensive methane predictors are required. Within a livestock precision farming context, the objective of this work was to integrate real-time data on animal feeding behaviour with an in silico model for predicting the individual dynamic pattern of methane emission in cattle. The integration of real-time data with a mathematical model to predict variables that are not directly measured constitutes a software sensor. We developed a dynamic parsimonious grey-box model that uses as predictor variables either dry matter intake (DMI) or the intake time (IT). The model is described by ordinary differential equations.Model building was supported by experimental data of methane emissions from respiration chambers. The data set comes from a study with finishing beef steers (cross-bred Charolais and purebred Luing finishing). Dry matter intake and IT were recorded using feed bins. For research purposes, in this work, our software sensor operated off-line. That is, the predictor variables (DMI, IT) were extracted from the recorded data (rather than from an on-line sensor). A total of 37 individual dynamic patterns of methane production were analyzed. Model performance was assessed by concordance analysis between the predicted methane output and the methane measured in respiration chambers. The model predictors DMI and IT performed similarly with a Lin's concordance correlation coefficient (CCC) of 0.78 on average. When predicting the daily methane production, the CCC was 0.99 for both DMI and IT predictors. Consequently, on the basis of concordance analysis, our model performs very well compared with reported literature results for methane proxies and predictive models. As IT measurements are easier to obtain than DMI measurements, this study suggests that a software sensor that integrates our in silico model with a real-time sensor providing accurate IT measurements is a viable solution for predicting methane output in a large scale context.

Review: Alternative and novel feeds for ruminants: nutritive value, product quality and environmental aspects

Ruminant-based food production faces currently multiple challenges such as environmental emissions, climate change and accelerating food-feed-fuel competition for arable land. Therefore, more sustainable feed production is needed together with the exploitation of novel resources. In addition to numerous food industry (milling, sugar, starch, alcohol or plant oil) side streams already in use, new ones such as vegetable and fruit residues are explored, but their conservation is challenging and production often seasonal. In the temperate zones, lipid-rich camelina (Camelina sativa) expeller as an example of oilseed by-products has potential to enrich ruminant milk and meat fat with bioactive trans-11 18:1 and cis-9,trans-11 18:2 fatty acids and mitigate methane emissions. Regardless of the lower methionine content of alternative grain legume protein relative to soya bean meal (Glycine max), the lactation performance or the growth of ruminants fed faba beans (Vicia faba), peas (Pisum sativum) and lupins (Lupinus sp.) are comparable. Wood is the most abundant carbohydrate worldwide, but agroforestry approaches in ruminant nutrition are not common in the temperate areas. Untreated wood is poorly utilised by ruminants because of linkages between cellulose and lignin, but the utilisability can be improved by various processing methods. In the tropics, the leaves of fodder trees and shrubs (e.g. cassava (Manihot esculenta), Leucaena sp., Flemingia sp.) are good protein supplements for ruminants. A food-feed production system integrates the leaves and the by-products of on-farm food production to grass production in ruminant feeding. It can improve animal performance sustainably at smallholder farms. For larger-scale animal production, detoxified jatropha (Jatropha sp.) meal is a noteworthy alternative protein source. Globally, the advantages of single-cell protein (bacteria, yeast, fungi, microalgae) and aquatic biomass (seaweed, duckweed) over land crops are the independence of production from arable land and weather. The chemical composition of these feeds varies widely depending on the species and growth conditions. Microalgae have shown good potential both as lipid (e.g. Schizochytrium sp.) and protein supplements (e.g. Spirulina platensis) for ruminants. To conclude, various novel or underexploited feeds have potential to replace or supplement the traditional crops in ruminant rations. In the short-term, N-fixing grain legumes, oilseeds such as camelina and increased use of food and/or fuel industry by-products have the greatest potential to replace or supplement the traditional crops especially in the temperate zones. In the long-term, microalgae and duckweed of high-yield potential as well as wood industry by-products may become economically competitive feed options worldwide.

Inhibition of Rumen Methanogens by a Novel Archaeal Lytic Enzyme Displayed on Tailored Bionanoparticles

Methane is a potent greenhouse gas, 25 times more efficient at trapping heat than carbon dioxide. Ruminant methane emissions contribute almost 30% to anthropogenic sources of global atmospheric methane levels and a reduction in methane emissions would significantly contribute to slowing global temperature rises. Here we demonstrate the use of a lytic enyzme, PeiR, from a methanogen virus that infects Methanobrevibacter ruminantium M1 as an effective agent inhibiting a range of rumen methanogen strains in pure culture. We determined the substrate specificity of soluble PeiR and demonstrated that the enzyme is capable of hydrolysing the pseudomurein cell walls of methanogens. Subsequently, peiR was fused to the polyhydroxyalkanoate (PHA) synthase gene phaC and displayed on the surface of PHA bionanoparticles (BNPs) expressed in Eschericia coli via one-step biosynthesis. These tailored BNPs were capable of lysing not only the original methanogen host strain, but a wide range of other rumen methanogen strains in vitro. Methane production was reduced by up to 97% for 5 days post-inoculation in the in vitro assay. We propose that tailored BNPs carrying anti-methanogen enzymes represent a new class of methane inhibitors. Tailored BNPs can be rapidly developed and may be able to modulate the methanogen community in vivo with the aim to lower ruminant methane emissions without impacting animal productivity.

Effects of replacing rice bran with tamarind seed meal in concentrate mixture diets on the changes in ruminal ecology and feed utilization of dairy steers

Feed ingredients costs have been impacting the production cost. Attempts have been made to use local feed resources in order to reduce feed costs. The objective of this study was to identify effect of using crushed tamarind seed meal (TSM) in concentrate mixture on rumen fermentation, dry matter intake, and digestibility of dairy steers. Four rumen-fistulated dairy steers were used in a 4 × 4 Latin Square Design. Four levels of TSM were used to replace rice bran (RB) in the concentrate mixtures in four treatments (T1 = 0% replacement of RB, T2 = 30% replacement of RB, T3 = 60% replacement of RB, T4 = 100% replacement of RB). The findings revealed that replacement of TSM for RB resulted in similar digestibility of nutrients and intakes (P > 0.05). However, rumen fermentation parameters were remarkably improved, namely total VFA and the concentration of C3 especially at the highest level of replacements (100%, T4), (P < 0.05). Rumen protozoal population was found lowered in all replacements, especially those in higher levels of TSM replacement. Consequently, the rumen methane productions were significantly reduced. TSM can be a promising energy source to replace rice bran, hence lowering the cost of concentrate mixture.

Is rumination time an indicator of methane production in dairy cows?

As long as large-scale recording of expensive-to-measure and labor-consuming traits, such as dry matter intake (DMI) and CH₄ production (CH₄P), continues to be challenging in practical conditions, alternative traits that are already routinely recorded in dairy herds should be investigated. An ideal indicator trait must, in addition to expressing genetic variation, have a strong correlation with the trait of interest. Our aim was to estimate individual level and phenotypic correlations between rumination time (RT), CH₄P, and DMI to determine if RT could be used as an indicator trait for CH₄P and DMI. Data from 343 Danish Holstein cows were collected at the Danish Cattle Research Centre for a period of approximately 3 yr. The data set consisted of 14,890 records for DMI, 15,835 for RT, and 6,693 for CH₄P. Data were divided in primiparous cows only (PC) and all cows (MC), and then divided in lactation stage (early, mid, late, and whole lactation) to analyze the changes over lactation. Linear mixed models, including an animal effect but no pedigree, were used to estimate the correlations among traits. Phenotypic and individual level correlations between RT and both CH₄P and DMI were close to zero, regardless of lactation stage and data set (PC or MC). However, CH₄P and DMI were highly correlated, both across lactation stages and data sets. In conclusion, RT is unsuitable to be used as an indicator trait for either CH₄P or DMI. Our study failed to validate RT as a useful indicator trait for both CH₄P and DMI, but more studies with novel phenotypes can offer different approaches to select and incorporate important yet difficult to record traits into breeding goals and selection indexes.

Host genetics and the rumen microbiome jointly associate with methane emissions in dairy cows

Cattle and other ruminants produce large quantities of methane (~110 million metric tonnes per annum), which is a potent greenhouse gas affecting global climate change. Methane (CH4) is a natural by-product of gastro-enteric microbial fermentation of feedstuffs in the rumen and contributes to 6% of total CH4 emissions from anthropogenic-related sources. The extent to which the host genome and rumen microbiome influence CH4 emission is not yet well known. This study confirms individual variation in CH4 production was influenced by individual host (cow) genotype, as well as the host's rumen microbiome composition. Abundance of a small proportion of bacteria and archaea taxa were influenced to a limited extent by the host's genotype and certain taxa were associated with CH4 emissions. However, the cumulative effect of all bacteria and archaea on CH4 production was 13%, the host genetics (heritability) was 21% and the two are largely independent. This study demonstrates variation in CH4 emission is likely not modulated through cow genetic effects on the rumen microbiome. Therefore, the rumen microbiome and cow genome could be targeted independently, by breeding low methane-emitting cows and in parallel, by investigating possible strategies that target changes in the rumen microbiome to reduce CH4 emissions in the cattle industry.

Scrophularia striata Extract Supports Rumen Fermentation and Improves Microbial Diversity in vitro Compared to Monensin

In the search for natural alternatives to antibiotic feed additives, we compared the efficacy of two doses of Scrophularia striata extract [S. striata-Low at 40 and S. striata-High at 80 mg g^-1 dry matter (DM)] with monensin (monensin) and a negative control in the modulation of rumen fermentation, methane production and microbial abundance in vitro. Microbes were investigated using qPCR and 16S rRNA targeted sequencing. Data showed that the addition of S. striata increased production of total short chain fatty acids (SCFA) in comparison to both monensin and control (P = 0.04). The addition of S. striata increased acetate production, and increased propionate at the higher dosage (P < 0.001). Supplementation of S. striata lowered methane production (P < 0.001) compared to control but with no effect compared to monensin. Ammonia concentration decreased by 52% (P < 0.001) with S. striata-High supplementation (4.14 mmol L^-1) compared to control, which was greater than that of monensin (36%). The diversity of rumen bacteria was reduced (P < 0.001) for monensin and S. striata for both the number of observed OTUs and the Chao1 index. Quantitative analysis of Protozoa showed a decrease in the monensin treatment (P = 0.05) compared to control. Archaea copy numbers decreased equally in both S. striata-High and monensin treatments compared to the control group. Supplementation with S. striata increased relative abundances of Fibrobacteres (P < 0.001) and Planctomycetes (P = 0.001) in comparison to both the control and monensin treatments. Significant negative correlations were observed between the abundances of Bacteroides, Fusobacterium, and Succinivibrio genera and methane (r > -0.71; P ≤ 0.001). The abundance of Fibrobacter genera and total SCFA (r = 0.86), acetate (r = 0.75), and valerate (r = -0.51; P < 0.001) correlated positively. These results suggest that S. striata supplementation at 80 mg g^-1 DM inclusion, similar to monensin, supports rumen fermentation, lowers methane and ammonia production. However, S. striata supported rumen fermentation toward higher total SCFA and propionate production, while unlike monensin still supported a diverse rumen microbiome and an increase in cellulolytic bacteria such as Fibrobacter.

Methanobacterium formicicum as a target rumen methanogen for the development of new methane mitigation interventions: A review

Methanobacterium formicicum (Methanobacteriaceae family) is an endosymbiotic methanogenic Archaean found in the digestive tracts of ruminants and elsewhere. It has been significantly implicated in global CH₄ emission during enteric fermentation processes. In this review, we discuss current genomic and metabolic aspects of this microorganism for the purpose of the discovery of novel veterinary therapeutics. This microorganism encompasses a typical H₂ scavenging system, which facilitates a metabolic symbiosis across the H₂ producing cellulolytic bacteria and fumarate reducing bacteria. To date, five genome-scale metabolic models (iAF692, iMG746, iMB745, iVS941 and iMM518) have been developed. These metabolic reconstructions revealed the cellular and metabolic behaviors of methanogenic archaea. The characteristics of its symbiotic behavior and metabolic crosstalk with competitive rumen anaerobes support understanding of the physiological function and metabolic fate of shared metabolites in the rumen ecosystem. Thus, systems biological characterization of this microorganism may provide a new insight to realize its metabolic significance for the development of a healthy microbiota in ruminants. An in-depth knowledge of this microorganism may allow us to ensure a long term sustainability of ruminant-based agriculture.

Ruminal methane emissions, metabolic, and microbial profile of Holstein steers fed forage and concentrate, separately or as a total mixed ration

Few studies have examined the effects of feeding total mixed ration (TMR) versus roughage and concentrate separately (SF) on ruminant methane production. Therefore, this study compared differences in methane production, ruminal characteristics, total tract digestibility of nutrients, and rumen microbiome between the two feeding methods in Holstein steers. A total six Holstein steers of initial bodyweights 540 ± 34 kg were divided into two groups and assigned to a same experimental diet with two different feeding systems (TMR or SF) in a crossover design with 21 d periods. The experimental diet contained 73% concentrate and 27% forage and were fed twice a day. The total tract digestibility of crude protein, neutral detergent fibre, and organic matter were not affected by the two different feeding systems. Steers fed TMR emitted more methane (138.5 vs. 118.2 L/d; P < 0.05) and lost more gross energy as methane energy (4.0 vs. 3.5% gross energy intake; P = 0.005) compared to those fed SF. Steers fed TMR had greater (P < 0.05) total volatile fatty acid (VFA), ammonia-N concentrations and propionate proportion of total VFA at 1.5 h, whereas lower after that compared to steers fed SF. The greater (P < 0.05) acetate: propionate ratio at 4.5 h for steers fed TMR reflected the shift of H2 sink from propionate towards acetate synthesis. The lower (P < 0.05) isobutyrate and isovalerate proportions of total VFA observed in steers fed TMR implies decrease in net consumption of H2 for microbial protein synthesis compared to SF. There were no differences in both major bacterial and archaeal diversity between TMR and SF, unlike several minor bacterial abundances. The minor groups such as Coprococcus, Succiniclasticum, Butyrivibrio, and Succinivibrio were associated with the changes in ruminal VFA profiles or methanogenesis indirectly. Overall, these results indicate that SF reduces methane emissions from ruminants and increases propionate proportion of total VFA without affecting total tract digestion compared to TMR. There were no evidences that the response differed due to different major underlying microbial population.

Holistic Assessment of Rumen Microbiome Dynamics through Quantitative Metatranscriptomics Reveals Multifunctional Redundancy during Key Steps of Anaerobic Feed Degradation

Ruminant livestock is a major source of the potent greenhouse gas methane. The complex rumen microbiome, consisting of bacteria, archaea, and microbial eukaryotes, facilitates anaerobic plant biomass degradation in the cow rumen, leading to methane emissions. Using an integrated approach combining multidomain quantitative metatranscriptomics with gas and volatile fatty acid (VFA) profiling, we aimed at obtaining the most comprehensive picture of the active rumen microbiome during feed degradation to date. Bacterial, archaeal, and eukaryotic biomass, but also methane emissions and VFA concentrations, increased drastically within an hour after feed intake. mRNA profiling revealed a dynamic response of carbohydrate-active enzyme transcripts, transcripts involved in VFA production and methanogenesis. While the relative abundances of functional transcripts did not mirror observed processes, such as methane emissions, transformation to mRNA abundance per gram of rumen fluid echoed ruminant processes. The microbiome composition was highly individual, with, e.g., ciliate, Neocallimastigaceae, Prevotellaceae, Succinivibrionaceae, and Fibrobacteraceae abundances differing between cows. Microbiome individuality was accompanied by inter- and intradomain multifunctional redundancy among microbiome members during feed degradation. This likely enabled the robust performance of the anaerobic degradation process in each rumen. Neocallimastigaceae and ciliates contributed an unexpectedly large share of transcripts for cellulose- and hemicellulose-degrading enzymes, respectively. Methyl-reducing but not CO2-reducing methanogens were positively correlated with methane emissions. While Methanomassiliicoccales switched from methanol to methylamines as electron acceptors, Methanosphaera became the dominating methanol-reducing methanogen. This study for the first time linked rumen meta-omics with processes and enabled holistic insights into the contribution of all microbiome members to feed degradation. IMPORTANCE Ruminant animals, such as cows, live in a tight symbiotic association with microorganisms, allowing them to feed on otherwise indigestible plant biomass as food sources. Methane is produced as an end product of the anaerobic feed degradation in ruminants and is emitted to the atmosphere, making ruminant animals among the major anthropogenic sources of the potent greenhouse gas methane. Using newly developed quantitative metatranscriptomics for holistic microbiome analysis, we here identified bacterial, archaeal, and eukaryotic key players and the short-term dynamics of the rumen microbiome during anaerobic plant biomass degradation and subsequent methane emissions. These novel insights might pave the way for novel ecologically and economically sustainable methane mitigation strategies, much needed in times of global climate change.

Mitigating Methane: Emerging Technologies To Combat Climate Change's Second Leading Contributor

Methane (CH₄) is the second greatest contributor to anthropogenic climate change. Emissions have tripled since preindustrial times and continue to rise rapidly, given the fact that the key sources of food production, energy generation and waste management, are inexorably tied to population growth. Until recently, the pursuit of CH₄ mitigation approaches has tended to align with opportunities for easy energy recovery through gas capture and flaring. Consequently, effective abatement has been largely restricted to confined high-concentration sources such as landfills and anaerobic digesters, which do not represent a major share of CH₄'s emission profile. However, in more recent years we have witnessed a quantum leap in the sophistication, diversity and affordability of CH₄ mitigation technologies on the back of rapid advances in molecular analytical techniques, developments in material sciences and increasingly efficient engineering processes. Here, we present some of the latest concepts, designs and applications in CH₄ mitigation, identifying a number of abatement synergies across multiple industries and sectors. We also propose novel ways to manipulate cutting-edge technology approaches for even more effective mitigation potential. The goal of this review is to stimulate the ongoing quest for and uptake of practicable CH₄ mitigation options; supplementing established and proven approaches with immature yet potentially high-impact technologies. There has arguably never been, and if we do not act soon nor will there be, a better opportunity to combat climate change's second most significant greenhouse gas.

Quantification of Methane and Ammonia Emissions in a Naturally Ventilated Barn by Using Defined Criteria to Calculate Emission Rates

Simple Summary

Defined criteria for the application of the CO₂ balance method in a naturally ventilated barn provided reliable data. This specification enabled the acquisition and quantification of CH₄ and NH₃ in a naturally ventilated dairy barn, as well as detecting decreasing NH₃ emissions affected by supplementing an Acacia mearnsii condensed tannin extract to a dairy cattle ration. Moreover, long-term measurements were possible and can be used to examine feed-related mitigation strategies at a barn level in the future.

Abstract

Extensive experimentation on individual animals in respiration chambers has already been carried out to evaluate the potential of dietary changes and opportunities to mitigate CH₄ emissions from ruminants. Although it is difficult to determine the air exchange rate of open barn spaces, measurements at the herd level should provide similarly reliable and robust results. The primary objective of this study was (1) to define a validity range (data classification criteria (DCC)) for the variables of wind velocity and wind direction during long-term measurements at barn level; and (2) to apply this validity range to a feeding trial in a naturally cross-flow ventilated dairy barn. The application of the DCC permitted quantification of CH₄ and NH₃ emissions during a feeding trial consisting of four periods. Differences between the control group (no supplement) and the experimental group fed a ration supplemented with condensed Acacia mearnsii tannins (CT) became apparent. Notably, CT concentrations of 1% and 3% of ration dry matter did not reduce CH₄ emissions. In contrast, NH₃ emissions decreased 34.5% when 3% CT was supplemented. The data confirm that quantification of trace gases in a naturally ventilated barn at the herd level is possible.

Phenotypic relationships among methane production traits assessed under ad libitum feeding of beef cattle

Angus cattle from 2 beef cattle projects in which daily methane production (MPR) was measured were used in this study to examine the nature of the relationships among BW, DMI, and methane traits of beef cattle fed ad libitum on a roughage diet or a grain-based feedlot diet. In both projects methane was measured using the GreenFeed Emission Monitoring system, which provides multiple short-term breath measures of methane production. The data used for this study were from 119 Angus heifers over 15 d on a roughage diet and 326 Angus steers over 70 d on a feedlot diet. Mean (±SD) age, BW, and DMI were 372 ± 28 d, 355 ± 37 kg, and 8.1 ± 1.3 kg/d for the heifers and 554 ± 86 d, 577 ± 69 kg, and 13.3 ± 2.0 kg/d for the steers, respectively. The corresponding mean MPR was 212 g/d for heifers and 203 g/d for steers. Additional traits studied included methane yield (MY; MPR/DMI), methane intensity (MPR/BW), and 3 forms of residual methane production (RMP), which is a measure of actual minus predicted MPR. For RMP, RMP, and RMP predicted MPR were obtained by regression of MPR on BW, on DMI, and on both DMI and BW, respectively. The 2 data sets were analyzed separately using the same statistical procedures. For both feed types the relationships between MPR and DMI and between MPR and BW were both positive and linear. The correlation between MPR and DMI was similar to that between MPR and BW, although the correlations were stronger for the roughage diet ( = 0.75 for MPR vs. DMI; = 0.74 for MPR vs. BW) than the grain-based diet ( = 0.62 for MPR vs. DMI; = 0.66 for MPR vs. BW). The correlation between MY and DMI was negative and moderate for the roughage ( = -0.68) and grain-based ( = -0.59) diets, a finding that is different from the nonsignificant correlations reported in studies of cattle on a restricted roughage diet. The 3 RMP traits were strongly correlated ( values from 0.76 to 0.99) with each other for both the roughage and the grain-based diets, which indicates that using RMP to lower MPR could provide a result similar to using RMP in cattle. As feed intake (DMI) is more difficult to measure than BW, this result implies that under ad libitum feeding situations in which DMI cannot be measured, RMP can be used to identify higher- or lower-RMP animals with similar levels of effectiveness as RMP.

Supplementation of Pelleted Hazel (Corylus avellana) Leaves Decreases Methane and Urinary Nitrogen Emissions by Sheep at Unchanged Forage Intake

This study is the first to quantify the effects of hazel (Corylus avellana) leaves on methane and urinary nitrogen emissions, digestibility, nitrogen and the energy balance of ruminants. Four experimental pellets were produced with 0, 30% and 60% hazel leaves, the latter also with 4% polyethylene glycol. Hazel leaves gradually replaced lucerne. The diet was composed of the pellets and grass hay (80%: 20%). Six adult sheep were allocated to all four treatments in a 6 × 4 crossover design. Including hazel leaves did not affect the feed intake, but it decreased the apparent digestibility of organic matter and fibre, especially at the high level. Methane emission was reduced by up to 25 to 33% per day, per unit of intake and per unit of organic matter digested. Urinary nitrogen excretion decreased by 33 to 72% with increasing levels of hazel leaves. The treatment with polyethylene glycol demonstrated that tannins in hazel leaves caused significant shares of the effects. In conclusion, the current results indicated a significant potential of hazel leaves as forage for ruminants to mitigate methane and urinary nitrogen emissions. Even high dietary hazel leaf proportions were palatable. The lower digestibility needs to be compensated with easily digestible diet ingredients.

Dietary fat sources affect feed intake, digestibility, rumen microbial populations, energy partition and methane emissions in different beef cattle genotypes

The mitigation of enteric methane emission in beef cattle production is important for reducing feed energy loss and increasing environmental sustainability. The main objective of this study was to evaluate the effect of different oilseeds included in fermented total mixed rations (whole soyabean seed (SBS, control), whole kapok seed (KPS) and cracked oil palm fruit (OPF)) on feed intake, digestibility, rumen microbial populations, energy partition and methane emissions in different cattle genotypes (Charolais crossbred v. Japanese Black crossbred). Three Charolais crossbred and three Japanese Black crossbred bulls were studied in a replicated 3×3 Latin square experimental design; genotypes were analysed in separate squares including three periods of 21 days each and three dietary oilseed treatments fed ad libitum. The cattle were placed in a metabolic cage equipped with a ventilated head box respiration system for evaluating digestibility and energy balance. As compared with Charolais crossbred individuals, Japanese Black crossbred bulls showed consistently lower dry matter intake (15.5%, P0.05) or diet (P>0.05) under the experimental conditions and ranged from 5.8% to 6.0% of gross energy intake. This value is lower than that reported by the Intergovernmental Panel on Climate Change (6.5%) for cattle fed with low-quality crop residues or by-products. Thus, our results imply that the Japanese Black crossbred cattle consume less feed and emits less enteric methane than the Charolais crossbred does, mainly owing to its lower ME requirement for maintenance. The OPF diet could be used to replace SBS for high beef production, although further studies are required to evaluate their application across a wide range of beef production systems.

Climate mitigation by dairy intensification depends on intensive use of spared grassland

Milk and beef production cause 9% of global greenhouse gas (GHG) emissions. Previous life cycle assessment (LCA) studies have shown that dairy intensification reduces the carbon footprint of milk by increasing animal productivity and feed conversion efficiency. None of these studies simultaneously evaluated indirect GHG effects incurred via teleconnections with expansion of feed crop production and replacement suckler-beef production. We applied consequential LCA to incorporate these effects into GHG mitigation calculations for intensification scenarios among grazing-based dairy farms in an industrialized country (UK), in which milk production shifts from average to intensive farm typologies, involving higher milk yields per cow and more maize and concentrate feed in cattle diets. Attributional LCA indicated a reduction of up to 0.10 kg CO₂ e kg^-1 milk following intensification, reflecting improved feed conversion efficiency. However, consequential LCA indicated that land use change associated with increased demand for maize and concentrate feed, plus additional suckler-beef production to replace reduced dairy-beef output, significantly increased GHG emissions following intensification. International displacement of replacement suckler-beef production to the "global beef frontier" in Brazil resulted in small GHG savings for the UK GHG inventory, but contributed to a net increase in international GHG emissions equivalent to 0.63 kg CO₂ e kg^-1 milk. Use of spared dairy grassland for intensive beef production can lead to net GHG mitigation by replacing extensive beef production, enabling afforestation on larger areas of lower quality grassland, or by avoiding expansion of international (Brazilian) beef production. We recommend that LCA boundaries are expanded when evaluating livestock intensification pathways, to avoid potentially misleading conclusions being drawn from "snapshot" carbon footprints. We conclude that dairy intensification in industrialized countries can lead to significant international carbon leakage, and only achieves GHG mitigation when spared dairy grassland is used to intensify beef production, freeing up larger areas for afforestation.

Intake, digestibility, growth performance, and enteric methane emission of Brazilian semiarid non-descript breed goats fed diets with different forage to concentrate ratios

The aim of this study was to evaluate the intake, digestibility, growth performance, and enteric methane emissions of Brazilian semiarid non-descript breed goats (NDG) fed diets with different forage:concentrate ratios (100:0, 80:20, 60:40, 40:60, and 20:80) on a dry matter basis. Forty uncastrated male NDG with an average initial body weight of 13.3 kg ± 4.7 kg were distributed in a completely randomized design, with five treatments and eight replications. Ground Tifton-85 hay was used as forage and ground corn and soybean meal were used as concentrate. The sulfur hexafluoride tracer technique was used to measure methane emissions. The intake of dry matter, organic matter, crude protein, and ether extract increased linearly while the intake of neutral detergent fiber decreased linearly as the concentrate proportion increased (P < 0.05). The digestibility of dry matter and organic matter increased while the digestibility of neutral detergent fiber decreased as the concentrate level increased (P < 0.05). There were linear increases in final body weight, total weight gain, average daily gain, and feed efficiency (P < 0.0001). Methane emissions per unit of body weight (ranging from 1.9 to 0.5 g/kg), metabolic body weight (ranging from 3.9 to 1.2 g/kg), and dry matter intake (ranging from 58.8 to 21.9 g/kg) reduced linearly as the concentrate proportion increased (P < 0.01). Decreasing the forage to concentrate ratio in the diet decreased methane emission and increased growth performance of NDG. The 80:20 ratio could be considered more appropriate to reduce methane emissions from NDG, which did not change much at higher levels of concentrate.

Compositional mixed modeling of methane emissions and ruminal volatile fatty acids from individual cattle and multiple experiments

The aim of the study was to investigate the association of methane (CH) yields (g/kg DMI) with rumen VFA molar proportions and animal and diet-related covariates from individual animals and multiple experiments. The dataset available consisted of 284 measurements of CH yields for beef cattle from 6 experiments measured in indirect respiration chambers. A compositional modeling approach was employed where VFA measurements were considered as a whole, instead of in isolation, emphasizing their multivariate relative scale. The analysis revealed expected close groupings of acetate and butyrate; propionate and valerate; iso-butyrate and iso-valerate. Linear mixed models were then fitted to examine relationships between CH yield and VFA, represented by meaningful log-contrasts of components called compositional balances, while accounting for other animal and diet-related covariates and random variability between experiments. A compositional balance representing (acetate × butyrate)/propionate best explained the contribution of VFA to variation in CH yield. The covariates DMI, forage:concentrate proportion (expressed as a categorical variable diet type: high concentrate, mixed forage:concentrate or high forage), and diet ME were also statistically significant. These results provided new insights into the relative inter-relationships among VFA measurements and also between VFA and CH yield. In conclusion, VFA molar proportions as represented by compositional balances were a significant contributor to explaining variation in CH yields from individual cattle.

Effects of encapsulated nitrate on growth performance, nitrate toxicity, and enteric methane emissions in beef steers: Backgrounding phase

A long-term experiment was conducted to examine the effects of feeding encapsulated nitrate (EN) on growth, enteric methane production, and nitrate (NO) toxicity in beef cattle fed a backgrounding diet. A total of 108 crossbred steers (292 ± 18 kg) were blocked by BW and randomly assigned to 18 pens. The pens (experimental unit; 6 animals per pen) received 3 dietary treatments: Control, a backgrounding diet supplemented with urea; 1.25% EN, control diet supplemented with 1.25% encapsulated calcium ammonium NO (i.e., EN) in dietary DM, which partially replaced urea; or 2.5% EN, control diet supplemented with 2.5% EN (DM basis) fully replacing urea. Additionally, 24 steers were located in 4 pens and randomly assigned to 1 of the above 3 dietary treatments plus a fourth treatment: 2.3% UEN, control diet supplemented with 2.3% unencapsulated calcium ammonium NO (UEN) fully replacing urea. Animals in the additional 4 pens were used for methane measurement in respiratory chambers, and the pens (except UEN) were also part of the performance study (i.e., = 7 pens/treatment). The experiment was conducted for 91 d in a randomized complete block design. During the experiment, DMI was not affected by inclusion of EN in the diet. Feeding EN had no effect on BW, ADG, and G:F ( ≥ 0.57). Methane production (g/d) tended to decrease ( = 0.099) with EN and UEN, but yield (g/kg DMI) did not differ ( = 0.56) among treatments. Inclusion of EN in the diet increased ( ≤ 0.02) sorting of the diets in favor of large and medium particles and against small and fine particles, resulting in considerable increases in NO concentrations of orts without affecting DMI. Plasma NO-N and NO-N concentrations increased ( ≤ 0.05) for EN compared with Control in a dose response manner, but blood methemoglobin levels were below the detection limit. Nitrate concentration in fecal samples slightly increased (from 0.01% to 0.14% DM; < 0.01) with increasing levels of EN in the diet. In conclusion, EN can be used as a feed additive replacing urea in beef cattle during a backgrounding phase in the long term without NO intoxication or any negative effects on growth performance. In addition, the study confirmed that feeding EN tended to decrease enteric methane production in the long term.

Effects of grass silage quality and level of feed intake on enteric methane production in lactating dairy cows

The objective of this study was to determine the effect of level of feed intake and quality of ryegrass silage as well as their interaction on enteric methane (CH) emission from dairy cows. In a randomized block design, 56 lactating dairy cows received a diet of grass silage, corn silage, and a compound feed meal (70:10:20 on DM basis). Treatments consisted of 4 grass silage qualities prepared from grass harvested from leafy through late heading stage, and offered to dairy cows at 96 ± 2.4 (mean ± SEM) days in milk (namely, high intake) and 217 ± 2.4 d in milk (namely, low intake). Grass silage CP content varied between 124 and 286 g/kg of DM, and NDF content between 365 and 546 g/kg of DM. After 12 d of adaptation, enteric CH production of cows was measured in open-circuit climate-controlled respiration chambers for 5 d. No interaction between DMI and grass quality on CH emission, or on milk production, diet digestibility, and energy, and N retention was found ( ≥ 0.17). Cows had a greater DMI (16.6 vs. 15.5 kg/d; SEM 0.46) and greater fat- and protein-corrected milk (FPCM) yield (29.9 vs. 25.4 kg/d; SEM 1.24) at high than low intake (both ≤ 0.001). Apparent total-tract nutrient digestibility was not affected ( ≥ 0.08) by DMI level. Total enteric CH production (346 ± 10.9 g/d) was not affected ( = 0.15) by DMI level. A small, significant ( = 0.025) decrease at high compared with low intake occurred for CH yield (21.8 ± 0.59 g/kg of DMI; -4%). Methane emission intensity (12.8 ± 0.56 g/kg of FPCM; -12%) was considerably smaller ( ≤ 0.001) at high intake as a result of greater milk yields realized in early lactation. As grass quality decreased from leafy through late heading stage, FPCM yield and apparent total-tract OM digestibility declined (-12%; ≤ 0.015), whereas total CH production (+13%), CH yield (+21%), and CH emission intensity (+28%) increased ( ≤ 0.001). Our results suggest that improving grass silage quality by cutting grass at an earlier stage considerably reduces enteric CH emissions from dairy cows, independent of DMI. In contrast, losses of N in manure increased for the earlier cut grass silage treatments. The small increase in DMI at high intake was associated with a small to moderate reduction in CH emission per unit of DMI and GE intake. This study confirmed that enteric CH emissions from dairy cows at distinct levels of feed intake depend on the nutritive value and chemical composition of the grass silage.

Greenhouse gas emission intensity based on lifetime milk production of dairy animals, as affected by ration-balancing program

Smallholder dairying in India and other developing countries relies on low- and medium-productive animals, and the feeding is mainly based on crop residues and other agro-industrial by-products. The diets are generally nutritionally imbalanced, resulting in productive and reproductive inefficiencies. This also negatively affects the emission intensity (Ei). For the past 3 years, the National Dairy Development Board of India has been implementing large-scale ration-balancing (RB) program in field animals. The effect of feeding balanced rations on Ei was explored. A cradle to farm-gate life-cycle assessment, taking into account the lifespan milk production, was conducted on 163 540 lactating cows and 163 550 buffaloes in northern, southern, eastern and western India. The life-cycle assessment boundary included feed production, enteric fermentation and manure management during various stages of life. On the basis of economic allocation, emissions of methane (CH4) from enteric fermentation, CH4 from manure management, nitrous oxide from manure management and greenhouse gas (GHG), i.e. carbon dioxide (CO2), CH4 and nitrous oxide from feed production, contributed 69.9%, 6.3%, 9.6% and 14.2% in cows, and 71.6%, 7.4%, 12.6% and 8.4% in buffaloes, respectively, to the baseline (before RB) lifetime total GHG emissions. Average Ei based on economic, mass and digestibility allocation for ‘baseline versus after RB’ were 1.6 versus 1.1, 1.8 versus 1.2 and 1.7 versus 1.2 kg CO2-equivalent/kg fat and protein-corrected milk in cows and 2.3 versus 1.5, 2.5 versus 1.6 and 2.4 versus 1.5 kg CO2-equivalent/kg fat and protein-corrected milk in buffaloes, respectively. Feeding-balanced rations significantly improved milk production, but reduced Ei of milk on lifetime basis by 31.2% and 34.7% in cows and buffaloes, respectively. Implementation of RB program has shown considerable potential to reduce GHG emission intensity under smallholding dairy production system of India.

Global beef cattle methane emissions: yield prediction by cluster and meta-analyses

Methane yield values (MY; g methane/kg dry-matter intake) in beef cattle reported in the global literature (expanded MitiGate database of methane-mitigation studies) were analysed by cluster and meta-analyses. The Ward and k means cluster analyses included accounting for the categorical effects of methane measurement method, cattle breed type, country or region of study, age and sex of cattle, and proportion of grain in the diet and the standardised continuous variables of number of animals, liveweight and MY. After removal of data from outlier studies, meta-analyses were conducted on subsets of data to produce prediction equations for MY. Removing outliers with absolute studentised residual values of >1, followed by meta-analysis of data accounting for categorical effects, is recommended as a method for predicting MY. The large differences among some countries in MY values were significant but difficult to interpret. On the basis of the datasets available, a single, global MY or percentage of gross energy in feed converted to methane (Ym) value is not appropriate for use in Intergovernmental Panel on Climate Change (IPCC) greenhouse accounting methods around the world. Therefore, ideally country-specific MY values should be used in each country’s accounts (i.e. an IPCC Tier 2 or 3 approach) from data generated within that country.

Optimal dose of 3-nitrooxypropanol for decreasing enteric methane emissions from beef cattle fed high-forage and high-grain diets

The objective of the present study was to determine the dose response of the methane (CH4) inhibitor 3-nitrooxypropanol (NOP) on enteric CH4 production and dry matter intake (DMI) for beef cattle fed a high-forage or high-grain diet. Fifteen crossbred yearling steers were used in two consecutive studies (high-forage backgrounding, high-grain finishing), each designed as an incomplete block with two 28-day periods with a 7-day washout in between and treatments corresponding to six doses of NOP (0 (Control), 50, 75, 100, 150, 200 mg/kg DM). The NOP was provided in the ration daily with the dose increased gradually over the first 10 days of each period. No treatment effects were observed on overall DMI or DMI of cattle when they were in the chambers either for the high-forage (P ≥ 0.54) or high-grain (P ≥ 0.26) diet. With the high-forage diet, NOP supplementation lowered total CH4 emissions (g/day) (P = 0.05), with the response at 200 mg NOP/kg DM different from Control (P < 0.05). Similarly, CH4 emissions corrected for DMI (g/kg DMI) and as a percentage of gross energy intake were linearly reduced in the high-forage diet with supplemental NOP (P < 0.01) and responses observed at 100, 150 and 200 mg NOP/kg DM differed from Control (P < 0.05). For the high-grain diet, total CH4 emissions decreased with incremental increases in the concentration of NOP supplemented (P = 0.04) and responses observed at 150 and 200 mg/kg DM differed from Control. Similarly, linear responses were observed with CH4 emissions corrected for DMI (P = 0.04) and gross energy intake (P = 0.02), with 100–200 mg NOP/kg DM differing from Control. Overall, results from the present study demonstrated that for beef cattle fed high-forage and high-grain diets, supplementation of 100–200 mg NOP/kg DM lowered enteric CH4 emissions without inducing any negative effects on DMI.

Effect of individual Ayurveda plants and mixtures thereof on in vitro ruminal fermentation, methane production and nutrient degradability

In order to identify new ways to mitigate methane emissions from ruminants, six medicinal plants, Achyranthes aspera, Azadirachta indica, Andrographis paniculata, Helicteres isora, Tinospora cordifolia and Piper longum, were evaluated in vitro with respect to ruminal fermentation and methanogenesis. A three-stage approach with n = 6 per treatment was applied. Two 24-h Hohenheim gas test experiments were performed by incubating the plants first as sole substrate and then added to a basal diet (10 g/kg diet DM). Finally, in a 10-day Rusitec experiment, A. paniculata, P. longum and T. cordifolia were supplemented individually and in all binary combinations to a basal diet (25 g/kg DM). Provided as sole substrate, all plants, except P. longum, decreased methane and carbon dioxide production (P < 0.05), and reduced the methane : short-chain fatty acid ratio (P < 0.05) in the Hohenheim gas test. In Rusitec, none of the individual supplements decreased methane production. The combination of A. paniculata with P. longum as a supplement was effective in mitigating the methane : carbon dioxide ratio and simultaneously maintaining feeding value. In conclusion, all medicinal plants incubated as sole substrate, except P. longum, possess anti-methanogenic properties, especially T. cordifolia, A. indica and H. isora. When supplemented at the levels investigated, they were mostly neutral with respect to rumen fermentation and nutrient digestion. Combining A. paniculata with P. longum mitigated methane without side effects on general ruminal fermentation. Further investigations, carried out in vivo, will demonstrate how useful this plant combination is in ruminant nutrition.