G. Molano

Methane emissions from beef cattle – a comparison of paddock- and animal-scale measurements

Methane (CH4) emissions from a herd of 58 grazing cattle were determined in a field experiment using paddock-scale (micrometeorological) methods. The emissions were also measured daily from each animal, using the sulfur hexafluoride tracer method. The paddock-scale methods exploit how the gas, once emitted from the cattle, is transported and dispersed by the wind. Hence, the emission rate may be calculated from measurements of windspeed, wind direction and turbulence statistics, as well as CH4 concentration upwind and downwind of the herd. The paddock-scale methods include a mass-budget approach, flux-gradient method and gas dispersion model. Accuracy can be assessed in unprecedented detail because the animal-scale (reference) method included all individuals in the herd, and the measurement site was ideal for micrometeorological methods (flat, usually windy and free of obstructions that alter the turbulent airflow). The cattle were hand-reared steers of average weight 325 ± 20 kg. Based on the animal-scale method, the average CH4 emission rate over 9 days was 161 ± 20 g/steer.day. The gas dispersion model, when utilising vertical concentration profiles, yielded on average 27% greater emissions. The other paddock-scale methods agreed with the animal-scale method, provided the cattle were at least 22 m away from the location of the downwind concentration measurements. When the cattle were allowed to graze as closely as 5 m from the instruments, the paddock-scale methods gave greater emissions than the animal-scale method; reasons for this are discussed.

The effect of level of intake and forage quality on methane production by sheep

In an experiment to determine the effect of level and quality of forage intake on methane (CH4) emissions, 16 wether lambs were allocated over two periods to two dietary treatments consisting of ryegrass at two stages of physiological maturity: an advanced stage of flowering and seeding (reproductive phase) and before flowering (vegetative phase). Additionally, in each period the lambs were divided into four groups and fed differing levels of food, from three-quarters maintenance to twice maintenance, to ensure a range of dry matter intakes amongst lambs. Apparent in vivo digestibility was measured and the mean values were 62.5% and 75.3% (s.e.d. = 0.84) for reproductive and vegetative ryegrass, respectively. Methane emissions were measured with the sulfur hexafluoride tracer technique. Daily methane emission was highly correlated with the amount of dry matter intake (DMI) (R2 = 0.83) and the regression was similar for both types of feed. Mean CH4 emissions per unit of DMI were 23.7 and 22.9 g/kg DMI (s.e.d. = 0.59) for reproductive and vegetative phases of ryegrass, respectively. The CH4 emissions per unit of DMI were not related to either level of DMI or diet quality.

Fumaric acid supplements have no effect on methane emissions per unit of feed intake in wether lambs

Recent reports suggest that supplementing the diet of ruminants with up to 10% fumaric acid (FA) can produce large reductions in methane (CH4) emissions, but the results have been equivocal. This trial evaluates the potential of FA to reduce enteric CH4 emissions from 18-month-old wethers fed lucerne. On two occasions, methane emissions were measured on 20 wethers fed a diet of dried ground lucerne with FA added to the diet at 0, 4, 6, 8 and 10 g FA/100 g dry matter (n = 4 wethers/treatment). Individual daily CH4 emissions were estimated using the sulfur hexafluoride (SF6) tracer gas technique together with measurements of daily dry matter intake (DMI) and total faecal output. Rumen samples were collected twice during the treatment periods in order to evaluate the effect of FA on rumen pH. There was a significant negative regression between FA% in the diet and CH4 emissions/day. However, the addition of FA did not affect CH4 emissions/kg DMI because high levels of FA supplementation reduced DMI. Rumen pH increased linearly with increasing level of FA supplementation. In conclusion, the effect of FA on CH4 emissions in this trial was associated with the resulting reduction in DMI and there were no decreases in CH4 emissions/kg DMI.

Lambs Fed Fresh Winter Forage Rape (Brassica napus L.) Emit Less Methane than Those Fed Perennial Ryegrass (Lolium perenne L.), and Possible Mechanisms behind the Difference

The objectives of this study were to examine long-term effects of feeding forage rape (Brassica napus L.) on methane yields (g methane per kg of feed dry matter intake), and to propose mechanisms that may be responsible for lower emissions from lambs fed forage rape compared to perennial ryegrass (Lolium perenne L.). The lambs were fed fresh winter forage rape or ryegrass as their sole diet for 15 weeks. Methane yields were measured using open circuit respiration chambers, and were 22-30% smaller from forage rape than from ryegrass (averages of 13.6 g versus 19.5 g after 7 weeks, and 17.8 g versus 22.9 g after 15 weeks). The difference therefore persisted consistently for at least 3 months. The smaller methane yields from forage rape were not related to nitrate or sulfate in the feed, which might act as alternative electron acceptors, or to the levels of the potential inhibitors glucosinolates and S-methyl L-cysteine sulfoxide. Ruminal microbial communities in forage rape-fed lambs were different from those in ryegrass-fed lambs, with greater proportions of potentially propionate-forming bacteria, and were consistent with less hydrogen and hence less methane being produced during fermentation. The molar proportions of ruminal acetate were smaller and those of propionate were greater in forage rape-fed lambs, consistent with the larger propionate-forming populations and less hydrogen production. Forage rape contained more readily fermentable carbohydrates and less structural carbohydrates than ryegrass, and was more rapidly degraded in the rumen, which might favour this fermentation profile. The ruminal pH was lower in forage rape-fed lambs, which might inhibit methanogenic activity, shifting the rumen fermentation to more propionate and less hydrogen and methane. The significance of these two mechanisms remains to be investigated. The results suggest that forage rape is a potential methane mitigation tool in pastoral-based sheep production systems.

The effect of oils fed to sheep on methane production and digestion of ryegrass pasture

Selecting ryegrass for higher concentrations of lipid to increase dietary energy density may increase the productivity of pasture-fed animals and reduce rumen methane emissions. A proof-of-concept study was undertaken to identify responses of sheep to increasing dietary lipid intake. Sheep housed in metabolism crates were fed fresh ryegrass at 120% of ad libitum intake for two 17-day periods with dry matter intake (DMI) and energy balance measured over the final 7 days and methane over five consecutive days at the end of each period. A blend of linseed and sunflower oils (3 : 1) were infused directly into the rumen of 8-month-old wether sheep (37 ± 1.7 kg [mean ± s.d.]; n = 2 per level) to provide 0% (control), 1.2%, 2.5%, 3.7%, 5.0% and 6.2% of DMI. Sheep were re-randomised among treatments for the second measurement period. Oils were infused over 2 h during each of the morning and afternoon feeding period at rates calculated to achieve the target addition. Measurements included DMI, energy intake and digestibility, enteric methane production and rumen volatile fatty acid (VFA) profiles. Sheep tolerated additional oil up to 5% of DMI, but when 6.2% was given, intakes declined and this treatment was discontinued. Up to 5% oil infusion did not affect methane production, DMI, energy digestibility or rumen VFA concentrations or proportions. The results suggest plant breeding to increase fatty acid content may benefit production provided total lipid did not exceed 9% of the DM, but methane production during digestion would be unaffected.

Methane emissions from dairy cattle divergently selected for bloat susceptibility

Bloat susceptibility is a genetically inherited trait and this study explored whether cattle divergently selected for this trait (low or high bloat susceptibility) also differ in methane (CH4) emissions. Twelve low bloat (402 ± 12 kg liveweight, LW) and 12 high bloat (334 ± 13 kg LW) Friesian × Jersey mixed age (2–4 years old) non-lactating and non-pregnant female cattle were used in a late autumn (June) grazing experiment involving two periods (P1 and P2). Methane emissions were measured during 5 (P1) or 4 (P2) consecutive days using the sulfur hexafluoride (SF6) tracer technique. In P1 only, titanium dioxide (TiO2) was used for faecal output and feed dry matter intake (DMI) estimations and it was found that the selection lines did not differ in DMI per unit of LW (17.3 ± 1.3 v. 15.4 ± 1.3 g DMI/kg LW, P > 0.05; for low and high bloat cows, respectively). In both periods, the mean absolute CH4 emissions from low bloat cows were significantly higher (P   0.05) either at P1 (346 ± 16 v. 312 ± 11 mg/kg LW) or P2 (345 ± 11 v. 347 ± 10 mg/kg LW). In P1, when DMI was estimated using TiO2, the selection lines did not differ (P > 0.05) in CH4 yields per unit of intake (20.6 ± 0.8 v. 21.3 ± 1.4 g/kg DMI for low and high bloat, respectively). Previous studies with the same herd showed that the selection lines did not differ in DMI per unit of LW, which was confirmed by the present study from estimations of DMI by TiO2 dosing in P1. It is concluded that low and high bloat susceptible genotypes did not differ in their CH4 yields per unit of feed intake.

Methane emissions from weaned lambs measured at 13, 17, 25 and 35 weeks of age compared with mature ewes consuming a fresh forage diet

Daily methane (CH4) emissions and dry matter intake (DMI) were measured on 14 mature ewes (3–4 years old) and 13 lambs when the lambs were 13, 17, 25 and 35 weeks of age. During the four CH4 measurement periods, all animals were kept in individual metabolism cages and fed pasture cut daily and fed at 1.5 times maintenance. Feed was offered in equal amounts at 0800 and 1500 hours daily. Methane emissions were measured using the sulfur hexafluoride tracer technique and values reported were the mean of measurement on 4–5 days for each animal. In the intervals between CH4 measurements, ewes and lambs grazed separate paddocks containing predominantly ryegrass. Daily CH4 emissions for the ewes ranged from 21.5 to 22.5 ± 1.50 g/day and were significantly higher than those of the lambs which ranged from 10.7 to 17.5 ± 1.50 g/day. Averaged across all four periods, the overall mean CH4 emission for lambs was 8% lower (P < 0.05) than for ewes (21.9 v. 23.8 ± 0.95 g CH4/kg DMI). However, within each measurement period, the emissions of CH4/kg DMI from lambs was significantly lower (P < 0.05) than those of ewes only in the fourth period when the lambs were 35 weeks of age (17.9 v. 21.9 g/kg DMI for lambs and ewes, respectively). The pasture offered to both ewes and lambs in this period was of higher quality than in the other periods (organic matter digestibility of 80% DM v. 68–71% DM at other times) and CH4 emission per kg DMI was lower in both groups of animals than in the other periods. This study supports the hypothesis that young sheep have lower CH4 emissions per unit of intake than mature animals. However, the age at which the lambs produced similar CH4/kg DMI to adult sheep could not be determined precisely because of the changes in pasture quality between different measurement periods.

Effect of fresh pasture forage quality, feeding level and supplementation on methane emissions from growing beef cattle

The objectives of this study were to determine the effect of fresh pasture forage quality (vegetative and mature pasture in different seasons), feeding level and supplementation with maize silage or palm kernel expeller on methane (CH4) production (g/day) and yield (g/kg dry matter intake; DMI) in growing beef cattle. The null hypothesis was that pasture quality, DMI level and supplementation have no effect on the CH4 yield (g/kg DM) in beef cattle. Four experiments were conducted and in three experiments (Exp. 1–3) freshly cut vegetative or mature pasture was fed to 14 growing beef animals in two consecutive periods, respectively, at intake levels of 1.5, 1.8 and 1.1 × maintenance metabolisable energy requirements (MEm) in Exp. 1–3, respectively. For Exp. 3, 100% maize silage was fed in a third consecutive period to the same cattle used in Periods 1 and 2. In Exp. 4, 4 animals were fed one of three treatments at 1.6 × MEm of 100% fresh pasture, fresh pasture supplemented with 35% DM maize silage or fresh pasture supplemented with 35% DM palm kernel expeller. After acclimatisation to respective diets, DMI and CH4 were measured for 12 animals in individual open circuit respiration chambers for two consecutive days in each experiment. Methane yield (g/kg DMI) was similar when animals were fed vegetative or mature pasture in Exp. 1 (20.0) and 2 (25.8), whereas in Exp. 3 feeding vegetative pasture resulted in a higher CH4 yield (25.7; P < 0.05) compared with feeding mature pasture (23.3), with feeding 100% maize silage intermediate (23.8). Methane yield of cattle fed pasture supplemented with maize silage in Exp. 4 was 10% higher (P < 0.05) compared with cattle fed mature pasture only or supplemented with palm kernel expeller (25.9, 23.3, 23.4 g/kg DMI, respectively). The regression between DMI and CH4 yield was similar for vegetative and mature pasture and pasture composition could explain up to 26% of variation in CH4 yield (P < 0.05). The CH4 yield in cattle fed 100% pasture (Exp. 1–3) was not affected by DMI and averaged 24.1 ± 2.78 g/kg DMI. In conclusion, fresh pasture forage quality, feeding level and supplementation had only minor, but some significant, effects on CH4 yield in beef cattle.

Enteric methane and carbon dioxide emissions measured using respiration chambers, the sulfur hexafluoride tracer technique, and a GreenFeed head-chamber system from beef heifers fed alfalfa silage at three allowances and four feeding frequencies

The objective of this study was to determine methane (CH) and carbon dioxide (CO) emissions from 8 beef heifers (approximately 20 mo of age and 382 ± 24.3 kg BW) measured by respiration chambers and the sulfur hexafluoride (SF) tracer technique and a mobile head-chamber, spot-sampling system (GreenFeed; C-Lock Inc., Rapid City, SD) when fed alfalfa silage at 3 feeding levels and 4 feeding frequencies. Feeding frequency may affect CH yield (g/kg DMI), and measurement systems (such as GreenFeed or SF) are needed to obtain accurate estimates of CH emissions from individual cattle under grazing where new pasture is provided once or twice daily. The Hereford × Friesian heifers were used in 5 consecutive periods (P1 to P5) of 14 d with CH and CO emissions measured with the SF technique in wk 1 (5-6 d), with chambers in wk 2 (2 d), and with the GreenFeed system when not in chambers (8 d) of each period. Alfalfa silage was restricted to 6, 8, 8, and 8 kg DM/d in P1, P2, P3, and P4, respectively, and provided ad libitum (10.9-12.2 kg DM/d) in P5. Silage was fed in 2, 2, 3, and 4 meals per day in P1, P2, P3, and P4, respectively, and was continuously available (refilled twice daily) in P5. Methane production increased from 141 to 265 g/d as DMI doubled ( < 0.001), but average CH yields measured in respiration chambers (24.5 g/kg DMI) and by the SF technique (22.8 g CH/kg DMI) and the GreenFeed system (26.2 g/kg DMI) were unaffected by feeding management ( = 0.6 for chambers and SF and = 0.06 for GreenFeed). The CH yields estimated by the GreenFeed system did not differ from CH yields estimated by the chambers in P1, P2, P3, and P5 but were greater ( < 0.02) than CH yields estimated by the SF technique in P2, P3, P4, and P5. Yields of CO (g/kg DMI) decreased with increasing DMI ( < 0.04) and CO production (g/d) increased from 5,293 to 9,167 g/d as DMI increased ( < 0.001). In general, the SF technique and the GreenFeed system provided means for CH yield that were not different from those of respiration chambers, and CH yields (g/kg DMI) were unaffected by DMI level or feeding frequency.

Methane emissions from lactating and non-lactating dairy cows and growing cattle fed fresh pasture

Currently, a fixed methane (CH4) emission factor is used for calculating total CH4 emissions from cattle in the national greenhouse gas inventory of New Zealand, independent of diet composition, cattle class (beef, dairy) or physiological state (growing, lactating, non-lactating). The objectives of this study were to determine CH4 emissions from lactating and non-lactating dairy cows (118 dairy cows; 81 lactating and 37 non-lactating, over 10 periods) and growing dairy heifers (12 measured twice) fed 100% fresh pasture forage in respiration chambers, which in combination with the published data of beef cattle (36 measured twice) fed fresh pasture were used to determine the relationship between CH4 emissions and dry matter intake (DMI), feed quality, cattle class (dairy vs beef) and physiological state (lactating, non-lactating and growing). Before regression analysis the dominant variables (DMI, CH4) needed to be transformed using natural logarithms (Ln) to make the variation in CH4 emissions more homogeneous across the range of data (i.e. stabilise the variance). Over all periods, average DMI ranged from 3.1 to 13.9 kg/day, average CH4 production from 64 to 325 g/day and average CH4 yield from 21.4 to 26.5 g/kg DMI. The DMI alone explained 90.8% of the variation in CH4 production (LnCH4 (g/day) = 3.250 + 0.9487 × LnDMI). Regression was improved to a minor extent (<3%, with associated increased prediction error) by including physiological status, cattle class or dietary composition in the model, in addition to LnDMI, on LnCH4 production. In conclusion, DMI alone was the strongest predictor for CH4 emissions from cattle fed fresh pasture with minor but irrelevant improvements in the prediction when considering pasture quality, cattle class or physiological status.