Enteric Methane Emissions and Animal Performance in Dairy and Beef Cattle Production: Strategies, Opportunities, and Impact of Reducing Emissions.

Effects of genetic line and feeding system on methane emissions from dairy systems

Enteric and manure-derived methane emissions and biogas yield of slurry from dairy cows fed grass silage or maize silage with and without supplementation of rapeseed

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

SUMMARYA mechanistic model (COWPOLL) was used to estimate enteric methane (CH4) emissions from beef production systems in Chile. The results expressed as a proportion of gross energy intake (GEI) were compared with enteric fermentation data reported in the last Chilean greenhouse gases inventory, which utilized an earlier the Intergovernmental Panel on Climate Change Tier 2 approach. The simulation analysis was based on information from feedstuffs, dry matter intake (DMI), body weight (BW) and average daily gain (ADG) of steers raised and finished at two research facilities located in Central and Southern Chile, as well as three simulated scenarios for grass-based finishing systems in Southern Chile. Data for feedlot production systems in the central region were assessed by considering steers fed a forage : concentrate ratio of 23 : 77 using maize silage and wheat straw as roughage sources during the stages of backgrounding and fattening. Average DMI were 7·3±0·62 and 9·2±0·55 kg/day per steer for backgrounding and fattening, respectively, whereas ADG were 1·1±0·22 and 1·3±0·37 kg/day for backgrounding and fattening. For the Southern Chilean fattening production systems, the forage : concentrate ratio was 56 : 44 with ryegrass pasture as the sole forage source. In this case, average DMI was 9·97±0·51 and ADG was 1·1±0·24 kg/day per steer. Two of the grass-based scenarios used the same initial BW information as that used for the Central and Southern Chilean systems, but feedlot diets were replaced by ryegrass pasture. The third grass-based scenario used an initial BW of 390 kg. In all the grass-based scenarios an ADG of 0·90 kg/day, with maximum DMI estimated as a proportion of BW (0·01 of NDF, kg/kg BW), was assumed. The results of the simulation analysis showed that emission factors (Ym; fraction of GEI) ranged from 0·062 to 0·079 of GEI. Smaller values were associated with finishing systems that included a lower proportion of forage in the diet due to higher propionate production, which serves as a sink for hydrogen in the rumen. Cattle finished in feedlot systems had an average of 0·062 of GEI lost as CH4, whereas grass-based cattle had losses of 0·079 of GEI. Enteric CH4 emissions for the systems using grass-based and concentrate diets were 261 and 159 g/kg weight gain, respectively. The Chilean CH4 inventory employs a fixed Ym of 0·060 to estimate enteric fermentation for all cattle. This value is lower than the average Ym obtained in the current simulation analysis (0·071 of GEI), which results in underestimation of enteric CH4 emissions from beef cattle. However, these results need to be checked against field measurements of CH4 emissions. Implementation of mechanistic models in the preparation of national greenhouse gas inventories is feasible if appropriate information is provided, allowing dietary characteristics and regional particularities to be taken into consideration.

Effects of plant-bound condensed tannin (CT)-containing sainfoin vs. CT-free alfalfa (or low-CT alfalfa-sainfoin mixture), plant stage of maturity, and their interaction on enteric methane (CH4) emissions, diet digestibility, and N excretion were studied, using 8 ruminally cannulated beef heifers in 2 sequential short-term experiments (Exp. 1 and 2). In Exp. 1, first growth legumes were harvested daily and offered fresh to heifers. Heifers were assigned to 100% sainfoin or 80% alfalfa:20% sainfoin (as-fed basis). Responses were measured at early (late vegetative to early bud; stage 2 to 3) and late (early flower; stage 5) stage of maturity. In Exp. 2, the same legumes were harvested from second growth (late bud; stage 4) and offered to heifers as hay; 100% sainfoin or 100% alfalfa. In both experiments, heifers were fed once daily at 1× maintenance. When fed as fresh forage (Exp. 1), sainfoin, compared with the alfalfa-sainfoin blend, had greater digestibility of OM (74.7 vs. 70.9%; P = 0.02), yet tended to have lower CP digestibility (73.2 vs. 77.1%; P = 0.059). There was no difference between fresh legumes for CH4 emissions [25.9 g/kg DMI ± 4.02 SE; 8.5% of gross energy intake (GEI) ± 1.26 SE; or 36.8 g/kg digested OM ± 1.75 SE]. The fresh legumes were more digestible at early, rather than at late, maturity and, consequently, enteric CH4 (27.4 vs. 24.4 g/kg DMI; P < 0.004; 8.9 vs. 8.1% GEI; P < 0.008) was greater at early, rather than at later, growth. When fed as hay (Exp. 2), sainfoin, compared with alfalfa, had greater digestibility of OM (60.5 vs. 50.3%; P = 0.007), lower digestibility of CP (64.2 vs. 68.8%; P = 0.004), yet there was no difference between the legume hays for CH4 emissions (22.4 g/kg DMI ± 1.29 SD and 7.1% GEI ± 0.40 SD). However, on the basis of OM digested, CH4 emissions were lower for sainfoin than alfalfa hay (44.3 vs. 59.0 g/kg; P = 0.008). Percentage of total N excretion in urine was less for sainfoin compared with alfalfa, both for fresh legumes in Exp. 1 (74 vs. 78%; P = 0.017) or hay in Exp. 2 (64 vs. 72%; P < 0.001), and increasing maturity lowered urinary N excretion. In conclusion, feeding CT-containing sainfoin partially shifted N excretion from urine to feces, but it had little impact on enteric CH4 emissions from beef cattle fed at maintenance as compared with feeding either 80% alfalfa:20% sainfoin (fresh forages) or 100% alfalfa (hay). Feeding fresh legumes harvested between the late vegetative to early bud stage, compared with harvested at the early flower stage, increased N excreted in urine as well as enteric CH4 emissions from beef cattle fed at maintenance.

At 27% of U.S. methane (CH4) emissions (3% of U.S. total emissions), enteric CH4 emissions represent the largest source of U.S. CH4 emissions, surpassing natural gas systems according to the latest report from the Environmental Protection Agency (EPA). Total manure CH4 emissions represent 1% of total U.S. emissions. Enteric and manure CH4 emissions from the beef industry represent 2.1% and 0.03%, respectively, of U.S. total emissions. These contributions of CH4 emissions to total U.S. greenhouse gas emissions are determined by relating CH4 emissions to a carbon dioxide (CO2) equivalent basis (CO2-e) by multiplying the amount of CH4 emissions by its global warming potential (EPA uses 25 for CH4 on a 100-y basis; GWP100). The GWP100 method was adopted following the Kyoto Protocol in 1997, and ever since this time its appropriateness for short-lived climate forcers (SLCF; e.g., CH4 has a 12-y atmospheric lifespan) has been debated. This debate exists because GWP100 is a misnomer, as it is known to have no relationship with the contribution of a gas to warming. Since CH4 is a SLCF, when emission rates are decreasing there is a decreasing concentration of CH4 in the atmosphere. To account for SLCF, an alternative accounting methodology, termed GWP-star (GWP*), has been proposed to convert SLCF to a CO2-warming equivalence (CO2-we). The CO2-we values from GWP* methodology has been demonstrated to closely relate to warming contributions compared with the CO2-e value from the GWP100 method. Applying the GWP* metric to enteric and manure CH4 emissions from the beef industry reduces the implied contribution to climate warming of these emission sources by 92% and 62%, on average from 2010-2020, respectively, compared with the GWP100 methodology. There are currently promising mitigation technologies emerging for mitigating enteric CH4 emission. For example 3-nitrooxypropanol may reduce enteric CH4 by 30% and Asparagopsis seaweed may reduce it by 80%. We explored the effects of these technologies on CO2-we if they had 100% adoption by the beef industry and if these mitigation potentials were consistent across all production systems (admittedly a big assumption). Both technologies would result in negative CO2-we for 20-y, after which a new baseline would be achieved and the CH4 emissions would begin contributing to warming again (i.e., accumulating CH4 in the atmosphere). During the 20-y of net-cooling, a 30% and 80% reduction in enteric CH4 would result in -143 (3% of U.S. total CO2 emissions) and -461 (10% of U.S. total CO2 emissions) million metric tons of CO2-we/y, respectively. Ultimately, adopting GWP* not only provides estimates that actually relate to contributions to climate warming, therefore providing a more appropriate metric than what is currently used, but also provides a means for the beef industry to leverage mitigation strategies to be a solution for climate change.

Symposium review: Uncertainties in enteric methane inventories, measurement techniques, and prediction models

Simple SummaryEnteric methane emissions produced by ruminant livestock has gained global interest due to methane being a potent greenhouse gas and ruminants being a significant source of emissions. In the absence of measurements, prediction models can facilitate the estimation of enteric methane emissions from ruminant livestock and aid investigation of mitigation options. This study developed a practical method using feed analysis information for predicting enteric methane emissions from sheep, beef cattle and dairy cows fed diets encompassing a wide range of nutrient concentrations. Enteric methane (CH4) is a by-product from fermentation of feed consumed by ruminants, which represents a nutritional loss and is also considered a contributor to climate change. The aim of this research was to use individual animal data from 17 published experiments that included sheep (n = 288), beef cattle (n = 71) and dairy cows (n = 284) to develop an empirical model to describe enteric CH4 emissions from both cattle and sheep, and then evaluate the model alongside equations from the literature. Data were obtained from studies in the United Kingdom (UK) and Australia, which measured enteric CH4 emissions from individual animals in calorimeters. Animals were either fed solely forage or a mixed ration of forage with a compound feed. The feed intake of sheep was restricted to a maintenance amount of 875 g of DM per day (maintenance level), whereas beef cattle and dairy cows were fed to meet their metabolizable energy (ME) requirement (i.e., production level). A linear mixed model approach was used to develop a multiple linear regression model to predict an individual animal’s CH4 yield (g CH4/kg dry matter intake) from the composition of its diet. The diet components that had significant effects on CH4 yield were digestible organic matter (DOMD), ether extract (EE) (both g/kg DM) and feeding level above maintenance intake: CH4 (g/kg DM intake) = 0.046 (±0.001) × DOMD − 0.113 (±0.023) × EE − 2.47 (±0.29) × (feeding level − 1), with concordance correlation coefficient (CCC) = 0.655 and RMSPE = 14.0%. The predictive ability of the model developed was as reliable as other models assessed from the literature. These components can be used to predict effects of diet composition on enteric CH4 yield from sheep, beef and dairy cattle from feed analysis information.

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.

Simple SummaryThe rumen microbiome plays a significant role in the breakdown of dietary substrates in the rumen and thus provides essential nutrients to the animals. However, methane (CH4) production by methanogens drains dietary energy. Therefore, manipulation of the rumen microbiome is one way to improve animal performance and reduce enteric methane emissions from ruminants. However, most previous studies have focused on dairy cattle at specific time points; thus, little is known about the rumen microbiome of steers and seasonal effects. This study aimed to compare the rumen microbiome, rumen fermentation and enteric CH4 emissions of Holstein and Jersey steers over different seasons. Both season and breed affected the rumen microbiome and rumen fermentation, while only breed affected enteric CH4 emissions. Our results suggest that both season and breed must be considered when manipulating the rumen microbiome to enhance animal performance. In addition, breed should be taken into consideration to reduce CH4 emissions from steers.Seasonal effects on rumen microbiome and enteric methane (CH4) emissions are poorly documented. In this study, 6 Holstein and 6 Jersey steers were fed the same total mixed ration diet during winter, spring, and summer seasons under a 2 × 3 factorial arrangement for 30 days per season. The dry matter intake (DMI), rumen fermentation characteristics, enteric CH4 emissions and rumen microbiota were analyzed. Holstein had higher total DMI than Jersey steers regardless of season. However, Holstein steers had the lowest metabolic DMI during summer, while Jersey steers had the lowest total DMI during winter. Jersey steers had higher CH4 yields and intensities than Holstein steers regardless of season. The pH was decreased, while ammonia nitrogen concentration was increased in summer regardless of breed. Total volatile fatty acids concentration and propionate proportions were the highest in winter, while acetate and butyrate proportion were the highest in spring and in summer, respectively, regardless of breed. Moreover, Holstein steers produced a higher proportion of propionate, while Jersey steers produced a higher proportion of butyrate regardless of season. Metataxonomic analysis of rumen microbiota showed that operational taxonomic units and Chao 1 estimates were lower and highly unstable during summer, while winter had the lowest Shannon diversity. Beta diversity analysis suggested that the overall rumen microbiota was shifted according to seasonal changes in both breeds. In winter, the rumen microbiota was dominated by Carnobacterium jeotgali and Ruminococcus bromii, while in summer, Paludibacter propionicigenes was predominant. In Jersey steers, Capnocytophaga cynodegmi, Barnesiella viscericola and Flintibacter butyricus were predominant, whereas in Holstein steers, Succinivibrio dextrinosolvens and Gilliamella bombicola were predominant. Overall results suggest that seasonal changes alter rumen microbiota and fermentation characteristics of both breeds; however, CH4 emissions from steers were significantly influenced by breeds, not by seasons.

Effect of concentrate feed level on methane emissions from grazing dairy cows

Diet supplementation with a mixture of essential oils: Effects on enteric methane emissions, apparent total-tract nutrient digestibility, nitrogen utilization, and lactational performance.

Effects of sheep breed and grass silage quality on voluntary feed intake and enteric methane emissions in adult dry ewes

Simple SummaryIn this study, we evaluated methane emissions from dairy cows fed grass or corn silage diets supplemented with rapeseed oil. Enteric methane emissions decreased on adding rapeseed oil to the diet, but methane emissions from feces of dairy cows fed diets supplemented with rapeseed oil did not differ. Thus, no trade-offs were observed between enteric and fecal methane emissions due to forage type or addition of rapeseed oil to diets fed to Swedish dairy cows.This study evaluated potential trade-offs between enteric methane (CH4) emissions and CH4 emissions from feces of dairy cows fed grass silage or partial replacement of grass silage with corn silage, both with and without supplementation of rapeseed oil. Measured data for eight dairy cows (two blocks) included in a production trial were analyzed. Dietary treatments were grass silage (GS), GS supplemented with rapeseed oil (GS-RSO), GS plus corn silage (GSCS), and GSCS supplemented with rapeseed oil (GSCS-RSO). Feces samples were collected after each period and incubated for nine weeks to estimate fecal CH4 emissions. Including RSO (0.5 kg/d) in the diet decreased dry matter intake (DMI) by 1.75 kg/d. Enteric CH4 emissions were reduced by inclusion of RSO in the diet (on average 473 vs. 607 L/d). In 9-week incubations, there was a trend for lower CH4 emissions from feces of cows fed diets supplemented with RSO (on average 3.45 L/kg DM) than cows with diets not supplemented with RSO (3.84 L/kg DM). Total CH4 emissions (enteric + feces, L/d) were significantly lower for the cows fed diets supplemented with RSO. Total fecal CH4 emissions were similar between treatments, indicating no trade-offs between enteric and fecal CH4 emissions.

Regional inventory of methane and nitrous oxide emission from ruminant livestock in the Basque Country