Sulfur Hexafluoride Tracer Technique Research Articles

SF6 Tracer Technique to Estimate Methane Emission in a Dual-Flow Continuous Culture System: Test and Application

This study aimed to evaluate the sulfur hexafluoride (SF6) tracer technique for estimating methane (CH4) emissions in dual-flow continuous culture systems (DFCCS). In experiment 1 (Exp1), fermenters were filled with water, and known CH4 concentrations (0, 1.35, 2.93, or 4.43 g/d) were injected using permeation tubes with SF6 release rates (3.30 or 9.65 mg/d). Headspace gas was collected using canisters, and the SF6 technique estimated CH4 recovery. Experiment 2 (Exp2) involved a DFCCS fermentation trial with ruminal fluid from three Holstein cows, testing diets with soybean meal or its partial replacement (50%) by Chlorella or Spirulina. Headspace gas was collected at intervals post-feeding. Standard curves for SF6 and CH4 quantification were inadequate for DFCCS samples, with the CH4:SF6 ratio differing from standards, indicating the data needs further SF6 release rate evaluation. In Exp1, a high correlation (r = 0.97) was found between infused and calculated CH4, indicating good repeatability. Low and high SF6 rates performed similarly at low CH4 infusion, but high SF6 overestimated CH4 at high infusion. Exp2 showed CH4 emissions irrespective of SF6 rate and indicated reduced CH4 emissions and increased NDF degradation with algae-containing diets. Further evaluation of the SF6 tracer technique is warranted for DFCCS.

Systematic review for optimizing sample size in dairy cow methane emission studies in temperate regions: a comprehensive methodological approach.

This research introduces a systematic framework for calculating sample size in studies focusing on enteric methane (CH4, g/kg of DMI) yield reduction in dairy cows. Adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we conducted a comprehensive search across the Web of Science, Scopus, and PubMed Central databases for studies published from 2012 to 2023. The inclusion criteria were: studies reporting CH4 yield and its variability in dairy cows, employing specific experimental designs (Latin Square Design (LSD), Crossover Design, Randomized Complete Block Design (RCBD), and Repeated Measures Design) and measurement methods (Open-circuit respirometry chambers (RC), the GreenFeed system, and the sulfur hexafluoride tracer technique), conducted in Canada, the United States and Europe. A total of 150 studies, which included 177 reports, met our criteria and were included in the database. Our methodology for using the database for sample size calculations began by defining 6 CH4 yield reduction levels (5, 10, 15, 20, 30, and 50%). Utilizing an adjusted Cohen's f formula and a power analysis we calculated the sample sizes required for these reductions in balanced LSD and RCBD reports from studies involving 3 or 4 treatments. The results indicate that within-subject studies (i.e., LSD) require smaller sample sizes to detect CH4 yield reductions compared with between-subject studies (i.e., RCBD). Although experiments using RC typically require fewer individuals due to their higher accuracy, our results demonstrate that this expected advantage is not evident in reports from RCBD studies with 4 treatments. A key innovation of this research is the development of a web-based tool that simplifies the process of sample size calculation (samplesizecalculator.ucdavis.edu). Developed using Python, this tool leverages the extensive database to provide tailored sample size recommendations for specific experimental scenarios. It ensures that experiments are adequately powered to detect meaningful differences in CH4 emissions, thereby contributing to the scientific rigor of studies in this critical area of environmental and agricultural research. With its user-friendly interface and robust backend calculations, this tool represents a significant advancement in the methodology for planning and executing CH4 emission studies in dairy cows, aligning with global efforts toward sustainable agricultural practices and environmental conservation.

The effects of feeding liquid or pelleted formulations of Asparagopsis armata to lactating dairy cows on methane production, dry matter intake, milk production and milk composition

Asparagopsis armata has been reported to have strong antimethanogenic effects when fed to dairy cows. The aim of this study was to evaluate the effect of a liquid and a pelleted formulation of A. armata when fed to lactating dairy cows as a supplemental feed twice daily at milking on i) enteric methane emissions, milk yield and dry matter intake (DMI), and ii) presence of halogenated compounds in milk, urine, faeces, and blood. Forty lactating, multiparous, Holstein-Friesian cows (117 ± 20.2 days in milk) were randomly allocated one of four treatments; 1) CON1: basal diet plus liquid supplement without A. armata, 2) AA1: basal diet plus liquid supplement with A. armata, 3) CON2: basal diet plus pellet supplement without A. armata, and 4) AA2: basal diet plus pellet supplement with A. armata. The liquid and pelleted supplements were offered twice daily for 34 days. Supplements were offered with a grain mix during each milking. The basal diet consisted of vetch hay ad libitum and 6.15 kg dry matter (DM)/d of a grain mix fed as 3.07 kg DM in the dairy per milking. Cows given the AA1 treatment received 298 mg bromoform per day while cows on the AA2 treatment received 293 mg bromoform per day. Individual forage DMI were measured daily via electronic monitoring of individual cows at the feed bins. Methane emissions were measured using the modified sulphur hexafluoride tracer technique on the last 5 days of the experiment. Feeding the A. armata formulations showed no effect on total DMI, forage DMI, concentrate DMI or milk yield. Methane production (g CH4/d), methane yield (g CH4/kg DMI) and methane intensity (g CH4/kg energy corrected milk) were reduced by about 20 % for both the liquid and the pelleted A. armata formulations. Feeding the A. armata formulations led to increased bromoform concentrations in milk (∼2.0 µg/L) but were well below the limit for safe consumption (100 µg/L). It is concluded that both formulations were effective in reducing enteric methane emissions and that milk from cows fed these A. armata formulations is safe for human consumption.

Heritability estimates and genome-wide association study of methane emission traits in Nellore cattle.

The objectives of the present study were to estimate the heritability for daily methane emission (CH4) and residual daily methane emission (CH4res) in Nellore cattle, as well as to perform genome-wide association studies (GWAS) to identify genomic regions and candidate genes influencing the genetic variation of CH4 and CH4res. Methane emission phenotypes of 743 Nellore animals belonging to 3 breeding programs were evaluated. CH4 was measured using the sulfur hexafluoride (SF6) tracer technique (which involves an SF6 permeation tube introduced into the rumen, and an appropriate apparatus on each animal), and CH4res was obtained as the difference between observed CH4 and CH4 adjusted for dry matter intake. A total of 6,252 genotyped individuals were used for genomic analyses. Data were analyzed with a univariate animal model by the single-step GBLUP method using the average information restricted maximum likelihood (AIREML) algorithm. The effects of single nucleotide polymorphisms (SNPs) were obtained using a single-step GWAS approach. Candidate genes were identified based on genomic windows associated with quantitative trait loci (QTLs) related to the 2 traits. Annotation of QTLs and identification of candidate genes were based on the initial and final coordinates of each genomic window considering the bovine genome ARS-UCD1.2 assembly. Heritability estimates were of moderate to high magnitude, being 0.42 ± 0.09 for CH4 and 0.21 ± 0.09 for CH4res, indicating that these traits will respond rapidly to genetic selection. GWAS revealed 11 and 15 SNPs that were significantly associated (P < 10-6) with genetic variation of CH4 and CH4res, respectively. QTLs associated with feed efficiency, residual feed intake, body weight, and height overlapped with significant markers for the traits evaluated. Ten candidate genes were present in the regions of significant SNPs; 3 were associated with CH4 and 7 with CH4res. The identified genes are related to different functions such as modulation of the rumen microbiota, fatty acid production, and lipid metabolism. CH4 and CH4res presented sufficient genetic variation and may respond rapidly to selection. Therefore, these traits can be included in animal breeding programs aimed at reducing enteric methane emissions across generations.

Twice daily feeding of canola oil steeped with Asparagopsis armata reduced methane emissions of lactating dairy cows

Red seaweeds have emerged as a potent methane-mitigating feed additive in ruminant diets. However, to date they have only been applied to production systems where total mixed rations (TMR) are given. New formulations are being developed to increase the application of red seaweeds, mainly Asparagopsis spp., across different production systems including those without TMR such as grazing-based systems. One product of interest is Asparagopsis armata steeped in edible oil (ASP-Oil) to extract and stabilise the primary antimethanogenic compound, bromoform. The aim of this study was to determine the effect of feeding two formulations of ASP-Oil, with (ASP-Oil 1) and without (ASP-Oil 2) the seaweed biomass removed, on enteric methane emissions, dry matter intake (DMI), milk yield and milk composition of dairy cows over 32 d. Thirty-nine lactating, multiparous, Holstein-Friesian (75 ± 20.6 days in milk) were randomly allocated to one of the three treatments; control (CON; basal diet + 134 g canola oil), ASP-Oil with the seaweed biomass removed (ASP1; basal diet + 134 g ASP-Oil 1), and ASP-Oil without the seaweed biomass removed (ASP2; basal diet + 145 g ASP-Oil 2 + 12 g canola oil). The treatments were given twice daily, using a pulse feeding technique, as a concentrate/oil supplement during each milking. The basal diet consisted of vetch hay ad libitum and 7.0 kg DM/d of a grain mix. Individual forage intakes were measured daily via electronic monitoring of individual cows at the feed bins. Methane emissions were measured using the modified sulphur hexafluoride tracer technique on days 27–32. At the rate of 136 g/d, there was no significant effect of treatment on DMI or milk yield, however during the transition period a rate of 268 g/d decreased hay intake. The supplementation of ASP1 and ASP2 decreased energy corrected milk (ECM; P = 0.029) compared to those cows offered the CON diet. Methane production (g/d) of cows given the ASP1 diet was 44 % lower than cows on the CON diet, methane yield (g/kg DMI) was 44 % lower, and methane intensity (g/kg ECM) was 38 % lower. For the ASP2 cows, the reductions were 39 % for methane production, 33 % for methane yield, and 31 % for methane intensity. Feeding the ASP-Oil increased bromoform concentrations in milk. However, the concentrations detected were demonstrated to be considerably lower than published safe concentrations in milk for human consumption (100 μg/L). These results show that the ASP-Oil has potential to be used as a methane mitigating feed additive when fed in a pulse feeding system.

Feeding incremental amounts of ground flaxseed: effects on diversity and relative abundance of ruminal microbiota and enteric methane emissions in lactating dairy cows.

We evaluated the effects of incremental amounts of ground flaxseed (GFX) on diversity and relative abundance of ruminal microbiota taxa, enteric methane (CH4) emissions, and urinary excretion of purine derivatives (PD) in lactating dairy cows in a replicated 4 × 4 Latin square design. Twenty mid-lactation Jersey cows were used in the study. Of these 20 cows, 12 were used for ruminal sampling, 16 for enteric CH4 measurements, and all for spot urine collection. Each period lasted 21 d with 14 d for diet adaptation and 7 d for data and sample collection. Diets were formulated by replacing corn meal and soybean meal with 0%, 5%, 10%, and 15% of GFX in the diet's dry matter. Ruminal fluid samples obtained via stomach tubing were used for DNA extraction. Enteric CH4 production was measured using the sulfur hexafluoride tracer technique. Diets had no effect on ruminal microbiota diversity. Similarly, the relative abundance of ruminal archaea genera was not affected by diets. In contrast, GFX decreased or increased linearly the relative abundance of Firmicutes (P < 0.01) and Bacteroidetes (P < 0.01), respectively. The relative abundance of the ruminal bacteria Ruminococcus (P < 0.01) and Clostridium (P < 0.01) decreased linearly, and that of Prevotella (P < 0.01) and Pseudobutyrivibrio (P < 0.01) increased linearly with feeding GFX. A tendency for a linear reduction (P = 0.055) in enteric CH4 production (from 304 to 256 g/d) was observed in cows fed increasing amounts of GFX. However, neither CH4 yield nor CH4 intensity was affected by treatments. Diets had no effect on the urinary excretion of uric acid, allantoin, and total PD. Overall, feeding GFX decreased linearly the relative abundance of the ruminal bacterial genera Ruminococcus and Clostridium and enteric CH4 production, but no change was seen for CH4 yield and CH4 intensity, or urinary excretion of total PD, suggesting no detrimental effect of GFX on microbial protein synthesis in the rumen.

Enteric Methane Emission from Sheep Fed with Rhodes Grass Hay (Chloris gayana) Alone or Supplemented with Dried Distillers’ Grains with Solubles

Livestock systems based on subtropical and tropical pastures are characterized by the low productivity of livestock due to the poor nutritional value of the forage (low nitrogen concentration and digestibility, and high fiber and lignin concentrations). These conditions lead to low productivity and, consequently, high absolute emissions of methane (CH4) per unit of product. Dry distilled grains with solubles (DDGS) are the main by-product resulting from ethanol production, and they are characterized by their high-energy fibrous and protein content, thus becoming an option for the supplementation of low-quality forage. This research investigated the effects of dietary DDGS inclusion on dry matter digestibility (DMD) and enteric CH4 emission. Eight adult sheep of 64 ± 8 kg live weight were used. The duration of the study was 54 days, divided into two periods (changeover design), which comprised a 17-day pre-experimental period and 10 days for experimental data collection. Animals were allocated to one of two treatments used: hay (H) as a control treatment, where animals were fed with Rhodes grass hay alone; and H + DDGS, where animals were fed with H supplemented with DDGS. CH4 emissions were estimated using the sulfur hexafluoride (SF6) tracer technique. Diets containing DDGS increased DMI by 22% (p &lt; 0.05) and reduced daily CH4 emissions by 24% (g/d), the CH4 yield by 35% (g/kg DMI), and the average value of CH4 energy per gross energy intake (Ym) by 44%, compared to the control treatment (p &lt; 0.05). The experiment demonstrated that supplementation with DDGS in low-quality roughage reduced daily CH4 emissions, yields, and Ym.

347 Enteric Methane: Current Measurement and Assessment Techniques

Abstract Enteric methane (ECH4) emissions from ruminants can be measured directly or indirectly using various techniques and recent reviews have discussed advantages and disadvantages of these techniques. The GLOBAL NETWORK project (GN; an international consortium of animal scientists) examined techniques for measuring ECH4, including respiration chambers, the sulfur hexafluoride tracer (SF6) technique, and techniques based on short-term measurements of gas concentrations in samples of exhaled air. The latter category includes automated head chambers (i.e., the GreenFeed system; GF), use of carbon dioxide as a marker, and (handheld) laser methane detection. The conclusion from this analysis was that “there is no ‘one size fits all’ method for measuring ECH4 emission by individual animals” and appropriate and frequent calibrations and recovery tests are necessary with all methods. The team also concluded that the need for screening large numbers of animals (for example, for genomic studies), does not justify the use of measurement methods that are inaccurate. Timing of sampling/data collection is critical for the spot-sampling techniques, such as GF. It is a well-established fact that ECH4 emission is closely related to animal’s dry matter intake (DMI) and feeding patterns. Therefore, data collection using GF has to be sufficiently long and frequent, during both day and night hours, to fully represent the diurnal patter of ECH4 emission. The in vitro gas production and analysis technique can be used to screen feed additives or other ECH4 mitigation treatments, but data must be always confirmed/supported by animal (preferably long-term) studies. ECH4 emission can be also predicted based on dietary or animal variables. Large databases developed by the GN project have confirmed that DMI is driving ECH4, but other factors, such as dietary neutral detergent fiber, milk yield and composition (dairy cows), or dietary forage inclusion and animal’s body weight (beef cattle) can improve prediction accuracy.

Effect of supplementing Leucaena leucocephalaleaves alone or in conjunction with malic acid on nutrient utilization, performance traits, and enteric methane emission in crossbred calves under tropical conditions.

Dietary strategies aiming at minimizing enteric methane (CH4) emission in ruminants are of practical interest from nutritional, economical, and environmental point of view. The present study evaluated the effects of supplementing Leucaena leucocephala leaves either alone or in conjunction with malic acid on nutrient utilization, growth performance, and enteric CH4 emission in crossbred cattle fed wheat straw and concentrate-based diet under tropical conditions. Eighteen crossbred (Karan-Fries) calves were randomly allocated into 3 groups: G-I (control)-fed wheat (Triticum aestivum) straw and concentrate mixture in the ratio 50:50; G-II-fed wheat straw, concentrate mixture, and Leucaena leucocephalaleaves in the ratio45:45:10; and (3) G-III-fed similar diet like G-II with an additional supplementation of 1% malic acid on dry matter intake basis. Experimental feeding spanning 90days included a 7-day metabolism trial and CH4 quantification study by sulfur hexafluoride tracer technique. Results revealed no significant effect of dietary treatments on dry matter intake (DMI) and digestibility of nutrients, except neutral detergent fiber (NDF) digestibility which was 5.5% higher (P < 0.05) in G-III as compared to control. Further, nitrogen (N) metabolism, rumen microbial protein synthesis, and growth performance remained similar among the treatments. No significant effect was also observed for enteric CH4 emission (expressed as g/day and g/kg DMI) in calves supplemented with Leucaena leucocephala leaves and malic acid. Therefore, the present findings depict modest improvement in fiber digestibility with no encouraging effect in mitigating enteric CH4 in growing cattle calves by supplementing Leucaena leucocephala leaves alone or with malic acid within the selected levels.

Measurement of Enteric Methane Emissions by the SF6 Technique Is Not Affected by Ambient Weather Conditions.

Simple SummaryAlthough the SF6 technique was developed over 25 years ago with the intention that it could be used to measure enteric methane production from ruminants outdoors, no experiments have reported the influence of ambient wind speed, temperature, humidity or rainfall on the accuracy of the technique. Six different cohorts of dairy cows (40 per cohort) were kept outdoors and fed a common diet during spring in 3 consecutive years. Individual cow feed intakes and daily methane productions were measured over 5 consecutive days and an automatic weather station measured air temperature, wind speed, relative humidity and rainfall every 10 min. Regression analyses were used to relate the average daily temperature, wind speed, humidity and rainfall to the average daily dry matter intake, methane production and methane yield of each cohort of cows. It was concluded that the modified SF6 technique can be used outdoors during a range of weather conditions without a significant effect on the measurement of methane production or methane yield of dairy cows.Despite the fact that the sulphur hexafluoride (SF6) tracer technique was developed over 25 years ago to measure methane production from grazing and non-housed animals, no studies have specifically investigated whether ambient wind speed, temperature, relative humidity and rainfall influence the accuracy of the method. The aim of this research was to investigate how these weather factors influence the measurement of enteric methane production by the SF6 technique. Six different cohorts of dairy cows (40 per cohort) were kept outdoors and fed a common diet during spring in 3 consecutive years. Methane production from individual cows was measured daily over the last 5 days of each 32-day period. An automated weather station measured air temperature, wind speed, relative humidity and rainfall every 10 min. Regression analyses were used to relate the average daily wind speed, average daily temperature, average daily relative humidity and total daily rainfall measurements to dry matter intake, average daily methane production and methane yield of each cohort of cows. It was concluded that the modified SF6 technique can be used outdoors during a range of wind speeds, ambient temperatures, relative humidities and rainfall conditions without causing a significant effect on the measurement of methane production or methane yield of dairy cows.

Use of infrared thermography to estimate enteric methane production in dairy heifers

ABSTRACT The trial aimed to investigate the use of infrared thermography (IRT) to estimate enteric methane production in dairy heifers. The study lasted 5 days with 36 Gyr, Gyr x Holstein and Holstein heifers. The sulphur hexafluoride (SF6) tracer technique was used to estimate methane emission. Superficial body temperature was obtained with an infrared camera (FLIR® T300) on each side of the animals at 20-minute intervals during eight hours after the morning feeding. Data were analysed using Pearson’s correlation analysis and multivariate regression analysis, as well as two multivariate tests to investigate the relationship with methane emission. The analysis considered all the data together (total) and three subsets: initial (0–150 minutes), middle (150–300) and final period (300–442 minutes after feeding). Based on R2 and canonical correlations, the best predictive capacity of methane emission by IRT occurred in the initial and final periods after feeding. Infrared thermography may be a good estimator of methane emission using the SF6-tracer technique when considering the flanks’ temperature.

230 Effects of encapsulated calcium-ammonium nitrate on performance and methane production of beef steers grazing mixed winter forage

Abstract The effects of encapsulated calcium-ammonium nitrate (eCAN) on in vivo methane production and performance were evaluated. A generalized randomized block design was used with beef steers grazing a mixed winter forage (Triticum aestivum, Triticosecale rimpaui, and Secale cereale) for 49 d. Thirty-six Angus-crossbred steers (332 ± 53 kg) were blocked by BW and randomly assigned to 1 of 3 treatments: 1) winter pasture + corn (WC), 2) WC + 328 mg/kg of BW eCAN (WCN) and 3) WC + 124 mg/kg of BW UREA (WCU), all supplemented with corn (0.3% BW treatments). Treatments WCN and WCU were isonitrogenous. A 14d adaptation period was used to adapt cattle to treatments. Methane emissions were measured using the sulfur hexafluoride tracer technique. Blood samples and BW were taken at d 0, 24, 35, and 49. Supplemental corn and NPN orts were collected daily. Data were analyzed using the MIXED procedure of SAS with the fixed effect of treatment and random effect of pasture (block); BUN, supplement intake and CP intake were analyzed with repeated measures. Steer was considered the experimental unit. Methane production was not different (P &amp;gt; 0.05) considering g/d, g/kg of BW, g/kg of MBW, or g/kg of ADG. Treatments did not affect ADG (P = 0.941). Supplement intake was affected by treatment (P &amp;lt; 0.001), with WC (0.979 kg) being greater compared to WCU (0.887 kg) and WCN (0.706 kg). Total CP intake increased (P &amp;lt; 0.001) with WCU (0.155 kg) and WCN (0.116 kg), compared to WC (0.074 kg), which did not have a non-protein source. Blood urea nitrogen was affected by day, with d 24 (18.598 mg/dL) being greater compared to d 0 (8.215 mg/dL), 35 (10.549 mg/dL) and 49 (14.5744 mg/dL). The eCAN did not effectively replace urea as a NPN source to mitigate enteric methane.

PSIX-2 Feeding 3-nitrooxypropanol reduces methane emissions by feedlot cattle

Abstract Our objective was to evaluate the effects of feeding 3-nitrooxypropanol (3NOP; Bovaer®, DSM Nutritional Products) at two doses on methane emissions and performance by feedlot cattle. The experiment was designed as a completely randomized block, in which 138 Nellore bulls (iBW, 360 ± 37.3 kg) were placed in collective pens (9 pens per treatment) and fed a high-concentrate diet (R:C, 11:89) according with the following three treatments: 1) 0ppm 3NOP /day; 2) 100ppm 3NOP/day, or 3) 150ppm 3NOP/day. For performance and DMI assessments the pen was the experimental unit. For methane emission evaluations, CH4 and DMI were assessed individually in 12 pens (2 bulls/pen, 8 bulls (experimental units)/treatment). Methane emission was measured for 6 consecutive days using the sulfur hexafluoride (SF6) tracer technique in two times over the experimental period (d15d -d21) and (105d to 111d), whereby the gross energy (GE) variables were calculated using equations. The individual DMI was measured using the two markers technique (Chromium oxide and indigestible NDF). The data were analyzed using the Mixed procedure of SAS and means comparison were carried out by Tukey’s test. Regardless of the level, dietary supplementation with 3NOP decreased (P &amp;lt; 0.001) methane emissions by 49.7% as expressed as g/d (146.0 vs. ~74 g/d−1); by 38.6% when expressed as g/kg ADG (91 vs ~56 g/kg ADG), and by 40.7% when expressed as g/kg DMI (13.5 vs. ~8 g/kg DMI). Likewise, dietary supplementation with 3NOP decreased (P &amp;lt; 0.001) the GE loss as a percentage of the GE intake by 42.4% (4.74 vs ~2.73%). However, feeding 3NOP had no effect on animalsˈ DM intake (~2.43 %BW; P = 0.23), ADG (~1.52 kg/d; P = 0.11) and HCW (~284 kg, P = 0.26). We conclude that Bovaer® can be used to effectively reduce methane emission by feedlot cattle without adverse effects on performance.

PSXII-6 Supplementation of Angus crossbred steers with avian-derived polyclonal antibody preparations against the ruminal methanogen Methanobrevibacter ruminantium M1 does not alter in vivo methane emissions

Abstract An experiment was conducted to evaluate the effect of supplementing twenty Angus crossbred steers with avian-derived polyclonal antibody preparations (PAP) against the ruminal methanogen Methanobrevibacter ruminantium M1 on in vivo methane production, using the sulfur hexafluoride (SF6) tracer technique (Johnson et al., 1994). Steers were fed chopped bermudagrass hay (BGH) ad libitum and 0.7 kg d-1 of corn gluten feed. The experiment followed a change-over design. Treatments were 1) supplementation of 3 mL d-1 of PAP against M. ruminantium M1 (PAP-M1), and 2) supplementation of 3 mL d-1 of a non-immunized egg product (CON). Individual BGH intake was recorded using an electronic radio-frequency monitoring system (GrowSafe System Ltd., Airdrie, Alberta, Canada). There was a 14-d adaptation period to the feeding regime, with no PAP supplementation, followed by an 18-d treatment period. Steers were dosed with brass permeation tubes with a known release rate of SF6 on d 7 of treatment period. Enteric methane emissions were sampled from d 13 to 18 of the treatment period, into N-rinsed pre-evacuated U-shaped polyvinyl chloride canisters (2 L) through a capillary tube. Methane emissions were averaged per animal within period. Data were analyzed as a change-over design using a model with fixed effects of order, period, and treatment and random effect of steer within order. Dry matter intake (DMI) was not different (P = 0.44) between treatments. Methane emissions, expressed as grams per day (P = 0.86), as grams per kilogram of DMI (P = 0.78), or in terms of methane emission factors (Ym, P = 0.78) were not different between PAP-M1 and CON treatments. Supplementation of steers with PAP against M. ruminantium M1 did not decrease enteric methane emissions. Based on preliminary ex situ trials, evaluation of different doses and combinations of PAP against other methanogenic species warrant further investigation.

Development of mathematical models to predict enteric methane emission by cattle in Latin America

Methane (CH4) is recognized as the second most important greenhouse gas (GHG) emitted by anthropogenic sources and is a major driver of climate change along with other GHG. Enteric fermentation CH4 emissions from ruminants contribute to approximately 17% of total global anthropogenic CH4 emissions. Several mathematical models to estimate enteric methane emissions have been published, but the majority are limited to cattle in developed countries. Therefore, our objective was to develop a set of empirical models to predict enteric CH4 emissions by cattle in Latin America (LA). A database was compiled from 67 publications that measured enteric CH4 emissions from cattle in LA using respiration chambers or the sulfur hexafluoride tracer technique. In total, there were 230 treatment means of enteric CH4 emissions measured from Nellore (n = 82), crossbreed (n = 79), Holstein (n = 45), and other breeds (n = 24). New prediction models were developed using a mixed-effects modeling approach with a random effect of study. Daily enteric CH4 emissions from all production systems ranged from 48.5 to 656 g/head with an average of 187 g/head. This large variation was largely explained by dry matter intake (DMI; RSR = 0.68, RMSPE = 29.1%). The prediction of CH4 emissions was further improved by a combination of DMI, digestibility and variables related to diet chemical composition such as dietary non-fibrous carbohydrates or dietary NDF. The best performance was obtained from the model based on DMI, dietary forage and organic matter digestibility (RSR = 0.59, RMSPE = 24.2% of observed mean). The newly developed models based on LA data give a better estimation of CH4 emissions from cattle than extant models, while the updated CH4 emission factors from IPCC 2019 performed better than emission factors of IPCC 2006. The new models developed using data specific to the region are recommended for use in preparing national methane inventories for LA cattle.

Animal performance, and enteric methane, manure methane and nitrous oxide emissions from Murrah buffalo calves fed diets with different forage-to-concentrate ratios

The present study aimed to evaluate the effects of dietary forage:concentrate ratios on growth performance and enteric and faecal greenhouse-gas emissions from growing buffalo calves. Fifteen Murrah male calves (bodyweight = 233.35 ± 30.92 kg; 8–12 months age) were randomly assigned to three dietary groups that were fed a mixture of berseem fodder, wheat straw and concentrate at the ratios of 20:60:20 (C20), 20:40:40 (C40) and 20:20:60 (C60) respectively, for 120 days. Enteric methane (CH4) production was estimated by the sulfur hexafluoride tracer technique. Faeces were stored for 12 weeks and CH4 and nitrous oxide (N2O) fluxes from stored faeces were estimated every 14 days. Dry-matter intake, feed conversion efficiency and nitrogen retention were not affected (P &amp;gt; 0.05) but average daily gain and urinary nitrogen loss (g/day) were higher for C60 than the C20 diet (P &amp;lt; 0.05). Daily enteric CH4 emission (g/day) was not affected but CH4 yield (g/kg dry-matter intake) and energy loss through CH4 as a proportion of energy intake were lower for C60 than the C20 diet (P &amp;lt; 0.05). Faeces composition was not affected, and large variations of greenhouse-gas emissions were observed for first 10 days of storage. Methane emissions from stored faces were 1.28 ± 0.40, 1.94 ± 0.34 and 3.90 ± 0.27 mg/kg faeces per day for C20, C40 and C60 diets respectively, being higher for C60 than the C40 and C20 diets (P &amp;lt; 0.05). Methane-flux rate from faeces was greater for C60 than the C20 and C40 diets (0.75 vs 0.26 and 0.37 g/animal respectively; P &amp;lt; 0.05). Diet C60 increased N2O fluxes from stored faeces by 63% and 58% respectively, expressed in mg/kg faeces per day and mg/animal per day, compared with C20 diet (P &amp;lt; 0.05). Overall, dietary concentrate proportion of up to 60% in growing buffalo calf diets improved growth performance without increasing enteric CH4 emission, but CH4 and N2O production from faeces were increased. This work has provided information for gas emissions factors from open storage of faeces. More detailed studies on gaseous emissions from open lots on farms are required.

Methane emission, ruminal fermentation parameters and fatty acid profile of meat in Santa Inês lambs fed the legume macrotiloma

Context Using legumes in ruminant production system may provide benefits such as improvement in animal performance and decrease in methane (CH4) emissions, mainly based on nutritional characteristics of these plants and the presence of tannins. Macrotiloma (Macrotyloma axillare) is a tropical legume that still lacks studies regarding its effects on animal performance and CH4 emissions. Aims The objective of this experiment was to evaluate productive performance, CH4 emission, ruminal fermentation parameters, carcass characteristics and fatty acid profile of the meat from lambs fed tropical grass hay supplemented with the legume forage macrotiloma. Methods For a 90-day experimental period, 14 Santa Inês male lambs (aging 100 days; 18.06 ± 3.26 kg initial bodyweight) were allocated in individual pens and divided into two treatments: chopped aruana grass (Panicum maximum cv. Aruana) hay (CON); aruana hay supplemented with chopped macrotiloma hay at a ratio of 75:25 grass to legume (MAC). Lambs were weighed fortnightly for calculation of average daily bodyweight gain (ADG) and CH4 emission was measured on three occasions (days 28 to 32; 57 to 61; 85 to 89) using the sulfur hexafluoride (SF6) tracer technique. At the last day of CH4 collection, rumen fluid samples were collected for: determination of ammoniacal nitrogen (NH3-N) and short chain fatty acids (SCFA); ruminal protozoa count; and relative abundance determination of general bacteria (BACT); Ruminococcus flavefaciens (RUMI); Fibrobacter succinogenes (FIBRO); methanogenic archaea (METH) by real-time quantitative PCR (real-time-qPCR) analysis. Subsequently, after 16 h fasting, the animals were slaughtered; carcass characteristics were then evaluated and longissimus thoracis samples were collected for fatty acid profile analysis. Key results No significant difference (P &amp;gt; 0.05) was observed between MAC and CON for productive performance, CH4 emission, SCFA and carcass characteristics. Reduced protozoa count and relative abundance of METH were observed for MAC (P &amp;lt; 0.05). Conclusions Despite the lack of effects on productive performance and CH4 emission, the decreased relative abundance of METH and protozoa count indicated that macrotiloma may possibly present anti-methanogenic activity. Implications The inclusion of this legume in the diet of ruminants may affect rumen microbes and potentially decrease environmental impacts of the production system.

Comparison of Methods to Measure Methane for Use in Genetic Evaluation of Dairy Cattle.

Simple SummaryMethane is a greenhouse gas with a global warming potential 28 times that of CO2. Enteric methane accounts for 17% of global methane emissions and 3.3% of total global greenhouse gas emissions from human activities. There is, therefore, significant research interest in finding ways to reduce enteric methane emissions by ruminants. Partners in Expert Working Group 2 (WG2) of the European Cooperation in Science and Technology (COST) Action METHAGENE have used several methods for measuring methane output by individual dairy cattle under various environmental conditions. Methods included respiration chambers, the sulphur hexafluoride (SF6) tracer technique, breath sampling during milking or feeding, the GreenFeed system, and the laser methane detector. Respiration chambers are considered the ‘gold standard’, but are unsuitable for large-scale measurements of methane emissions, which are needed for genetic evaluations. In this study, the suitability of methods for large-scale studies was reviewed and compared. All methods showed high correlations with respiration chambers, but comparisons among alternative methods generally had lower correlations. Results confirm, however, that there is sufficient correlation between methods for measurements from all methods to be combined, with appropriate weightings, for use in international genetic studies. This will pave the way for breeding cattle with lower methane emissions.Partners in Expert Working Group WG2 of the COST Action METHAGENE have used several methods for measuring methane output by individual dairy cattle under various environmental conditions. Methods included respiration chambers, the sulphur hexafluoride (SF6) tracer technique, breath sampling during milking or feeding, the GreenFeed system, and the laser methane detector. The aim of the current study was to review and compare the suitability of methods for large-scale measurements of methane output by individual animals, which may be combined with other databases for genetic evaluations. Accuracy, precision and correlation between methods were assessed. Accuracy and precision are important, but data from different sources can be weighted or adjusted when combined if they are suitably correlated with the ‘true’ value. All methods showed high correlations with respiration chambers. Comparisons among alternative methods generally had lower correlations than comparisons with respiration chambers, despite higher numbers of animals and in most cases simultaneous repeated measures per cow per method. Lower correlations could be due to increased variability and imprecision of alternative methods, or maybe different aspects of methane emission are captured using different methods. Results confirm that there is sufficient correlation between methods for measurements from all methods to be combined for international genetic studies and provide a much-needed framework for comparing genetic correlations between methods should these become available.

Effects of Dietary Forage Proportion on Feed Intake, Growth Performance, Nutrient Digestibility, and Enteric Methane Emissions of Holstein Heifers at Various Growth Stages.

Simple SummaryEnteric methane (CH4) emission from ruminants is a large source of anthropogenic greenhouse gas production, which is an inevitable by-product when feedstuff is digested and fermented in the rumen, representing approximately 7% of dietary energy loss. Although the Chinese government has committed to reduce CH4 emissions under the requirement of the Copenhagen Accord (2009), there is lack of accurate CH4 emission data from young cows as the guideline of IPCC gives little consideration to the variations of geographic conditions, animal physiology stages, and dietary components of dairy production system. Our study investigated the effects of different dietary forage-to-concentrate on feed intake, growth performance, nutrient digestibility, and enteric CH4 emissions of Holstein heifers under various growth stage, and developed the prediction equations using production and emission data. Our results demonstrated that enteric CH4 emission was significantly affected by dietary composition and physiological condition; results obtained from the current study will be of great importance for development of regional or national emission inventories and mitigation approaches for heifers at specific growth stage.Enteric methane (CH4) emissions from young ruminants contribute to a substantial proportion of atmospheric CH4 accumulation. Development of emission inventory and mitigation approaches needs accurate estimation of individual emission from animals under various physiological conditions and production systems. This research investigated the effect of different dietary concentrate contents on feed intake, growth performance, nutrient digestibility and CH4 emissions of heifers at various stages, and also developed linear or non-linear prediction equations using data measured by sulphur hexafluoride tracer technique. Increasing dietary concentrate contents increased feed intake and growth rate, enhanced nutrient digestibility, and reduced enteric CH4 emissions. Heifers at the age of 9, 12, and 15 months with an average weight of 267.7, 342.1, and 418.6 kg produced 105.2, 137.4, and 209.4 g/day of CH4, and have an average value of CH4 energy per gross energy intake (Ym) 0.054, 0.064, 0.0667, respectively. Equations relating CH4 emission values with animal and feed characteristics were developed with high determination coefficients for heifers at different growth stages. Dietary concentrate contents had significant influence on overall performance of heifers. These data can be used to develop regional or national emission inventories and mitigation approaches for heifers under various production regimes in China.

Could the breed composition improve performance and change the enteric methane emissions from beef cattle in a tropical intensive production system?

Crossbreeding has been used to improve performance in beef cattle, however the effects of breed composition on methane (CH4) production, yield and intensity from cattle raised in tropical intensive and integrated systems remain unknown. To assess the impact of breed composition on performance and methane emissions, Nellore (NEL; yr 1: BW = 171.5 ± 19.4 kg; n = 10; yr 2: BW = 215.8 ± 32.3 kg, n = 25) and Angus x Nellore crossbred (AN; yr 1: BW = 214.2 ± 26.4 kg, n = 10; yr 2: BW = 242.5 ± 32.2 kg, n = 25) were compared. The animals grazed on integrated crop-livestock system in the growing phase (stocking rate 2452 kg BW/ha, herbage mass 4,884 kg dry matter (DM)/ha, forage allowance 5.9 kg DM/100kg BW) and then were finished in a feedlot. Steers (n = 8) from each breed composition were randomly selected in each phase to measure CH4 production using a sulfur hexafluoride (SF6) tracer technique and DM intake (DMI) using titanium dioxide. Compared with NEL, AN had both superior total gain and average daily gain (ADG) in the grazing period. The AN presented greater ADG in the feedlot with a shorter finishing period and resulted in greater carcass yield and carcass ADG. Methane production (kg/period) was lower in NEL (19% less) than AN in grazing (P<0.01), and no difference was observed in feedlot. The NEL had less CH4 intensity (CH4/BW) in grazing but greater CH4 per unit of ADG in the feedlot compared to AN. Breed composition did not influence the CH4 yield (CH4/DMI) in either phase, despite the difference in feedlot DMI (kg/day). In conclusion, crossbreeding may be an option to improve performance and reduce the CH4 per ADG in tropical climate conditions, resulting in lower methane emission per kg of meat produced.