J.P. Goopy¹, C. Chang² and N. Tomkins³

Abstract Accurate measurement techniques are needed for determining greenhouse gas (GHG) emissions in order to improve GHG accounting estimates to IPCC Tiers 2 and 3 and enable the generation of carbon credits. Methane emissions from agriculture must be well defined, especially for ruminant production systems where national livestock inventories are generated. This review compares measurement techniques for determining methane production at different scales, ranging from in vitro studies to individual animal or herd measurements. Feed intake is a key driver of enteric methane production (EMP) and measurement of EMP in smallholder production systems faces many challenges, including marked heterogeneity in systems and feed base, as well as strong seasonality in feed supply and quality in many areas of sub-Saharan Africa.

In vitro gas production studies provide a starting point for research into mitigation strategies, which can be further examined in respiration chambers or ventilated hood systems. For making measurements under natural grazing conditions, methods include the polytunnel, sulphur hexafluoride (SF₆) and open-path laser. Developing methodologies are briefly described: these include blood methane concentration, infrared thermography, pH and redox balance measurements, methanogen population estimations and indwelling rumen sensors.

Table of contents: 

5.1 Introduction
5.2 Indirect estimation
5.3 Direct measurement
5.4 Short-term measurement
5.5 Emerging and future technologies
Author-affiliations
References

5.1      Introduction

Fermentation processes by rumen microbes result in the formation of reduced cofactors, which are regenerated by the synthesis of hydrogen (H₂) (Hungate 1966). Accumulation of excessive amounts of H₂ in the rumen negatively affects the fermentation rate and growth of some microbial consortia. Methanogens therefore reduce carbon dioxide (CO₂) to methane (CH₄) and water (H₂0) thereby capturing available hydrogen (McAllister et al. 1996). It is predicted that total CH₄ emissions from livestock in Africa will increase to 11.1 mt year^-1 by 2030, an increase of 42% over three decades (Herrero et al. 2008). Production increases and efficiencies in the livestock sector are seen as complementary outcomes if enteric methanogenesis can be reduced. While mitigation strategies are focused on manipulation of nutritional factors and rumen function, animal breeding programmes for selecting highly efficient animals that produce less enteric CH₄ might also be useful. Regardless of the mitigation strategy imposed, any reduction in enteric methane production (EMP) must be quantified and for this to be achieved, accurate baseline emissions data are essential.

This chapter reviews existing and developing methodologies for gathering accurate data on ruminant methane production under a wide range of production systems. The principles of using predictive algorithms based on dietary, animal and management variables are considered here for modelling smallholder livestock emissions, but not in detail. Predictive models have been considered in detail elsewhere (Blaxter and Clapperton 1965; Kurihara et al. 1999; Ellis et al. 2007, 2008; Charmley et al. 2008; Yan et al. 2009). Major techniques are highlighted at different levels — in vitro, animal, herd and farm scale — and their advantages and disadvantages, including implementation in practice, are discussed. These methodologies can be used to support mitigation strategies or quantify total national livestock emissions.

5.2      Indirect estimation

5.2.1      In vitro incubation

The amount of gas released from the fermentation process and the buffering of volatile fatty acids is related to the kinetics of fermentation of a known amount of feedstuff (Dijkstra et al. 2005). Several systems have been developed for measuring in vitro gas production, varying considerably in complexity and sophistication. Menke et al. (1979) describes a manual method using gas tight syringes, which involves constant registering of the gas volume produced. More recently others have described a system using pressure transducers (Pell and Schofield 1993; Theodorou et al. 1994; Cone et al. 1996). Variants of this system are now available as proprietary systems (RF, ANKOM Technology®) using radio frequency pressure sensor modules, which communicate with a computer interface and dedicated software to record gas pressure values.

The basic principle of the in vitro technique relies on the incubation of rumen inoculum with a feed substrate under an anaerobic environment in gas tight culture bottles. Gas accumulates throughout the fermentation process and a cumulative volume is recorded. Gas volume curves can be generated over time. To estimate kinetic parameters of total gas production, gas production values are corrected for the amount of gas produced in a blank incubation and these values can be fitted with time using a non-linear curve fitting procedure in GenStat (Payne et al. 2011) or other suitable software. Headspace gas samples are taken to analyse the gas compositions and determine actual CH₄ concentrations, typically by gas chromatography. A ‘quick and dirty’ alternative is to introduce a strongly basic solution, such as NaOH into the vessel, which will cause the CO₂ to enter solution. The remaining gas is assumed to be CH₄.

Gas is only one of the outputs of microbial fermentation, and the quality of the information derived can be improved by also considering substrate disappearance and production of volatile fatty acids (VFAs) (Blümmel et al. 2005).

5.2.2      Estimation from diet

EMP can be estimated from intake and diet quality (digestibility). A number of algorithms can be used to do this, although estimates of emissions can vary by 35% or more for a particular diet (Tomkins et al. 2011). Diet quality can be inferred from analysis of representative samples of the rations or pasture consumed, but where intake is not measured, estimation of EMP faces considerable challenges. Models which estimate intake based on diet quality or particular feed fractions assume ad libitum access, and in situations where animals are corralled without access to feed overnight, the validity of this assumption is likely violated (Jamieson and Hodgson 1979; Hendricksen and Minson 1980). In such a case, intake can be inferred from energy requirement (Live Weight (LW) + Energy for: LW flux; maintenance + lactation and pregnancy + locomotion) using published estimates (such as National Research Council) to convert physical values to energy values and so infer intake of the estimated diet. If this method is chosen, multiple measurements are required to capture changes in these parameters, as well as seasonal influences on feed availability and quality. Where possible, estimates made using this methodology should be validated by measurements in respiratory chambers.

5.3      Direct measurement

5.3.1      Open-circuit respiration chambers

Models to estimate national and global CH₄ emissions from sheep and cattle at farm level are mostly based on data of indirect calorimetric measurements (Johnson and Johnson 1995). Respiration chambers are used to measure CH₄ at an individual animal level. Their use is technically demanding, and only a few animals can be monitored at any one time (McGinn et al. 2008). However, these systems are capable of providing continuous and accurate data on air composition over an extended period of time.

Although the design of chambers varies, the basic principle remains the same. Sealed and environmentally controlled chambers are constructed to house test animals. All open-circuit chambers are characterized by an air inlet and exhaust, so animals breathe in a one-way stream of air passing through the chamber space. Air can be pulled through each chamber and, by running intake and exhaust fans at different speeds, negative pressure can be generated within the chamber. This is to ensure that air is not lost from the chamber (Turner and Thornton 1966). However, CH₄ can still be lost from chambers that are imperfectly sealed (down the concentration gradient), so gas recovery is an essential routine maintenance task. Thresholds for chamber temperature (<27°C), relative humidity (<90%), CO₂ concentration (<0.5%) and ventilation rate (250–260 L min^-1) have been described (Pinares-Patiño et al. 2011), but may vary in practice. It is very important, however, to ensure that test animals remain in their thermo-neutral zone while being measured, or intake is likely to be compromised. Some chambers may be fitted with air conditioning units, which provide a degree of dehumidification, and a ventilation system. This ensures that chambers can be maintained at constant temperature (Klein and Wright 2006) or at near-ambient temperature to capture normal diurnal variance (Tomkins et al. 2011). Choices about temperature are governed by technical resources and experimental objectives. Feed bins and automatic water systems may also be fitted with electronic scales and meters to monitor feed and water intake.

Change in O_2, CO₂ and CH₄ concentrations is measured by sampling incoming and outgoing air, using gas analysers, infrared photoacoustic monitors or gas chromatography systems (Klein and Wright 2006; Grainger et al. 2007; Goopy et al. 2014b). The other essential measurement is airflow, over a period of either 24 or 48 hours. The accuracy and long-term stability of the measurements are dependent on the sensitivity of the gas analysers used and the precision of their calibration. Chambers are directly calibrated by releasing a certain amount of standard gas of known concentration to estimate recovery values (Klein and Wright 2006). Measurement outcomes are also influenced by the environmental temperature, humidity, pressure, incoming air composition and chamber volume. The larger the chamber the less sensitive the measurements are to spatial fluctuations, as the response time is dependent on the size of the chamber and the ventilation rate (Brown et al. 1984). The calibration of the gas analysers must be accurate and replicable for long-term use.

One constraint of this technique is that normal animal behaviour and movement are restricted in the respiration chambers. Animals benefit from acclimatization in chambers prior to confinement and measurement, in order to minimize alterations in behaviour, such as decreased feed intake (McGinn et al. 2009). However, there is clear evidence that this will happen in a small proportion of animals, regardless of training (Robinson et al. 2014) and this should be borne in mind when interpreting data. Using transparent construction material in chamber design allows animals to have visual contact with the other housed animals.

There are high costs associated with the construction and maintenance of open-circuit respiration chambers. The need for high performance and sensitive gas analysers and flow meters must be considered in design and construction. Only a few animals can be used for measurements within chambers at any one time (Nay et al. 1994). Nevertheless, respiration chambers are suitable for studying the differences between treatments for mitigation strategies, and continue to be regarded as the ‘gold standard’ for measuring individual emissions.

5.3.2      Ventilated hood system

The ventilated hood system is a simplification of the whole animal respiration chamber, as it measures the gas exchange from the head only, rather than the whole body. Moreover, it is an improvement on face masks as used by Kempton et al. (1976), because gas measurements can be generated throughout the day and animals are able to access food and water.

Modern ventilated hood systems for methane measurements have been used in Japan, Thailand (Suzuki et al. 2007, 2008), USA (Place et al. 2011), Canada (Odongo et al. 2007) and Australia (Takahashi et al. 1999). Fernández et al. (2012) describes a mobile, open-circuit respiration system.

The ventilated hood system used by Suzuki et al. (2007, 2008) consists of a head cage, the digestion trial pen, gas sampling and analysis, behaviour monitoring and a data acquisition system. Similarly to whole animal chambers, it is equipped with a digestion pen for feed intake and excreta output measurements. An airtight head cage is located in front of the digestion pen and is provided with a loose fitting sleeve to position the animal’s head. Head boxes are provided with blowers, to move the main air stream from the inlet to the exhaust. Flow meters correct the air volume for temperature, pressure and humidity. Air filters remove moisture and particles from the gas samples, which are sent to the gas analysers (Suzuki et al. 2007). The mobile system of Fernández et al. (2012) contains a mask or a head hood connected to an open-circuit respiration system, which is placed on a mobile cart.

The ventilated hood system is a suitable method under some circumstances, especially where open-circuit chambers are not viable. A critical limitation of the hood system is that extensive training is absolutely essential to allow the test animals to become accustomed to the hood apparatus. Thus while it can be used to assess potential of feeds, it is not suitable for screening large numbers of animals. A further consideration is that hoods capture only measurements of enteric methanogenesis and exclude the proportion in flatus.

5.3.3      Polytunnel

Polytunnels are an alternative to respiration chambers, and operation and measurements are somewhat simpler. Methane emissions from individual or small groups of animals can be acquired under some degree of grazing. This allows test animals to express normal grazing behaviour, including diet selection over the forages confined within the polytunnel space. They have been used in the UK to measure CH₄ emissions from ruminants under semi-normal grazing conditions. Murray et al. (2001) reports CH₄ emissions from sheep grazing two ryegrass pastures and a clover–perennial ryegrass mixed pasture using this methodology. Essentially polytunnels consist of one large inflatable or tent type tunnel made of heavy duty polyethylene fitted with end walls and large diameter ports. Air is drawn through the internal space at speeds of up to 1 m³ s^-1 (Lockyer and Jarvis 1995). In general they are used where emissions from fresh forages are of interest because animals can be allowed to graze a confined area of known quality and quantity. When the available forage is depleted the tunnel is moved to a new patch.

Air flow rate can be measured at the same interval as the CH₄ or can be continuously sampled at the exhaust port (Lockyer 1997). Micropumps may be used to pass the exhausted air to a dedicated gas analyser or a gas chromatograph (GC) (Murray et al. 2001). Data from all sensors can be sent to a data logger, which captures flow rate, humidity and temperature within the tunnel, and gas production from the livestock. Samples of the incoming and exhaust air can be taken as frequently as necessary, depending on the accuracy required. The samples can be either taken manually or by an automatic sampling and injection system.

The polytunnel system requires frequent calibration to assure a good recovery rate, which is performed using the same principle as the chamber technique. Methane measurements can be collected over extended periods of time. Fluctuations occur due to changes in animal behaviour, position relative to the exhaust port, internal temperature, relative humidity and grazing pattern of the animal: eating, ruminating or resting (Lockyer and Jarvis 1995; Lockyer and Champion 2001). The polytunnel is suitable for measuring CH₄ emissions under semi-normal grazing conditions. It has been reported that the polytunnel method gives 15% lower readings of CH₄ concentration compared to the respiration chamber method, suggesting that animals actually consume less in the polytunnel. This requires further investigation. Recovery rate is high in both systems: 95.5–97.9% in polytunnels, compared to 89.2–96.7% in chambers (Murray et al. 1999). With an automated system, measurements can be performed with high repeatability. The system is portable and can be used on a number of pastures or browse shrubs, though again its utility is limited by the inability to capture feed intake.

5.3.4      Sulphur hexafluoride tracer technique

The sulphur hexafluoride (SF₆) technique provides a direct measurement of the CH₄ emission of individual animals. This technique can be performed under normal grazing conditions, but can also be employed under more controlled conditions where intake is measured and/or regulated.

The SF₆ principle relies on the insertion of a permeation tube with a predetermined release ratio of SF₆ into the rumen, orally administered (Johnson et al. 1994). Air from around the animal’s muzzle and mouth is drawn continuously into an evacuated canister connected to a halter fitted with a capillary tube around the neck. Johnson et al. (1994) provide a detailed description of the methodology.

The duration of collection of each sample is regulated by altering the length and/or diameter of the capillary tube (Johnson et al. 1994). Several modifications have since been reported with specific applications (Goopy and Hegarty 2004; Grainger et al. 2007; Ramirez-Restrepo et al. 2010). Most recently Deighton et al. (2014) has described the use of an orifice plate flow restrictor which considerably reduces the error associated with sample collection and should be considered in preference to the traditional capillary tube flow restrictors. At completion of sample collection the canisters are pressurized with N₂ prior to compositional analysis by gas chromatography. Enteric CH₄ production is estimated by multiplying the CH₄/SF₆ ratio by the known permeation tube release rate, corrected for actual duration of sample collection and background CH₄ concentration (Williams et al. 2011), which is determined by sampling upwind ambient air concentration. Williams et al. (2011) emphasized the importance of correct measurement and reporting of the background concentrations, especially when the method is applied indoors. CH₄ is lighter (16 g mol^-1) than SF₆ (146 g mol^-1) and will therefore disperse and accumulate differently depending on ventilation, location of the animals and other building characteristics.

This method enables gas concentrations in exhaled air of individual animals to be sampled and takes into account the dilution factor related to air or head movement. The high within- and between-animal variation is significant limitation of this method. Grainger et al. (2007) reported variation within animals between days of 6.1% and a variation among animals of 19.7%. Pinares-Patiño et al. (2011) monitored sheep in respiration chambers simultaneously with the SF₆ technique. They reported higher within (x 2.5) and between (x 2.9) animal variance compared to the chamber technique, combined with a lower recovery rate (0.8±0.15 with SF₆ versus 0.9±0.10 with chambers). These sources of variation need to be taken into account in order to determine the number of repeated measures necessary to ensure accurate results. Moate et al. (2015) describes the use of Michaelis–Menten kinetics to better predict the discharge rate of capsules, which should reduce error associated with estimating discharge rates. It should also prolong the useful life of experimental subjects through the improved predictability of discharge rates over much longer intervals.

The SF₆ technique allows animals to move and graze normally on test pastures. This makes the method suitable for examining the effect of grazing management on CH₄ emissions (Pinares-Patiño et al. 2007) but it does so at a cost. The SF₆ method is less precise, less physically robust (high equipment failures) and more labour intensive than respiration chamber measures.

5.3.5      Open-path laser

The use of open-path lasers combined with a micrometeorological dispersion method can now be used to measure enteric methane emissions from herds of animals. It therefore facilitates whole-farm methane measurements across a number of pastures.

The open-path laser method for whole-farm methane measurements is already in use in Canada (McGinn 2006; Flesch et al. 2005, 2007), Australia (Loh et al. 2008; McGinn et al. 2008; Denmead 2008; Tomkins et al. 2011), New Zealand (Laubach and Kelliher 2005) and China (Gao et al. 2010). Methane concentration measurements are performed using one or more tuneable infrared diode lasers mounted on a programmable and motorized scanning unit (Tomkins et al. 2011). The tuneable infrared diode laser beams to a retro reflector along a direct path, which reflects the beam back to a detector. The intensity of the received light is an indicator of the CH₄ concentration (ppm) along the path. In an optimal situation there should be at least one path for each predominant wind direction: one path upwind (background CH₄) and multiple paths downwind (CH₄ emission) of the herd. This method assumes that the herd acts as a surface source or, when individual animals can be fitted with GPS collars, individual animals are treated as point sources.

Regardless of application, the CH₄ concentration is calculated as the ratio of the external absorption to internal reference-cell absorption of the infrared laser beam as it travels along the path (Flesch et al. 2004, 2005). Methane concentration and environmental indicators such as atmospheric temperature, pressure, and wind direction and speed are continually measured and recorded using a weather station (Loh et al. 2008, 2009). Data — including GPS coordinates of the paddock or individual animals from a number of averaging time periods — can be merged using statistical software. After integrating, WindTrax software (Thunder Beach Scientific, Nanaimo, Canada) uses a backward Langrangian Stochastic (bLS) model to simulate CH₄ emissions (g day^-1 per animal), by computing the line average CH₄ concentrations with atmospheric dispersion conditions.

The data integrity of the open-path laser method is highly dependent on environmental factors and the location of test animals. Flesch et al. (2007) described several criteria to determine data integrity using the open-path laser method. These criteria are based on wind turbulence statistics, laser light intensity, R² of a linear regression between received and reference waveforms, surface roughness, atmospheric stability and the source location (surface or point source). Invalid data can be generated as a result of misalignment of the laser, unfavourable wind directions, surface roughness or periods in which the atmospheric conditions (rain, fog, heat waves, etc.) are unsuitable for applying the model (Freibauer 2000; Laubach and Kelliher 2005; Loh et al. 2008). To optimize the positioning of the equipment, these meteorological and physical aspects of the experimental site must be taken into account (Flesch et al. 2007; Loh et al. 2008, 2009). Moreover, the measurement area is restricted by the length of the laser paths when using a surface source approach. It is important to define the herd location, as uneven distribution of the herd results in miscalculations of the CH₄ concentration. Tomkins et al. (2011), comparing open-circuit respiration chambers with the open-path laser technique, reported estimated CH₄ emissions using the bLS dispersion model of 29.7±3.70 g kg^-1 dry matter intake (DMI), compared to 30.1±2.19 g kg^-1 DMI measured using open-circuit respiration chambers.

The open-path laser method does not interfere with the normal grazing behaviour of the cattle and is non-invasive. Spatial variability is taken into account in these measurements, as the method can simulate gas fluxes over a large grazing area. Moreover, the tuneable diode laser is highly sensitive and has a fast response to changes in CH₄ concentration, with detection limits at a scale of parts per trillion (McGinn et al. 2006). The labour intensity is low, although the equipment requires continuous monitoring. This method is expensive, which reflects not only the requirement for sensitive and rapid-response instruments to analyse CH₄ concentration, but also the requirement to capture micrometeorology data. Diurnal variations due to grazing and rumination pattern, pasture composition and individual variation need to be considered in planning experimental protocols to prevent over- or under- calculation of the total emission. Furthermore, DMI determination is not very accurate as this is based on predictive models using the relationship between LW and LW gain, following assumption of the ARC (1980).

5.4      Short-term measurement

While most assessments of enteric methane emissions are focused on daily methane production (DMP), or the derivative, daily methane yield (MY), there is increasing impetus to estimate the emissions of large numbers of animals in their productive environment. This is driven both by the demand for data to establish genetic parameters for DMP and to verify mitigation strategies or GHG inventories. This area is discussed only briefly here, as there is currently limited scope for the application of these technologies in sub-Saharan Africa. The area has been ably reviewed by Hegarty (2013).

5.4.1      Greenfeed® emission monitoring apparatus

Greenfeed® is a patented device (Zimmerman & Zimmerman 2012) that measures and records short-term (3–6 minute) CH₄ emissions from individual cattle repeatedly over 24 hours by attracting animals to the unit using a ‘bait’ of pelleted concentrate. By being available 24 hours per day potential sampling bias is reduced and the technique has been shown to provide comparable estimates to those produced both by respiratory chamber and SF₆ techniques (Hammond et al. 2013). However, a significant limitation of the technique is the requirement to supply an ‘attractant’ to lure the animal to use the facility, consisting of up to 1 kg of concentrate pellets per day. This will certainly affect DMP and may also alter volatile fatty acid profiles or the overall digestibility of the diet. Attempts to use energy neutral attractants, such as water have proven equivocal (J Velazco, pers. comm.).

5.4.2      Portable accumulation chambers (PAC)

A PAC consists of a clear polycarbonate box of approximately 0.8m³, open at the bottom and sealed by achieving close contact with flexible rubber matting. Methane production is measured by the increase in concentration that occurs while an animal is in the chamber for approximately 1 hour. PACs were designed to screen large numbers of sheep, variously to identify potentially low and high emitting individuals and to develop genetic parameter estimates in sheep populations. This technique initially showed close agreement with respiratory chamber measurements (Goopy et al. 2009; Goopy et al. 2011). Subsequent investigations demonstrated such measurements to be moderately repeatable in the field and to have potential for genetic screening of animals (Goopy et al. 2015). Longer-term comparisons of PAC measurements and respiratory chamber data, however, suggest that these two methods may be measuring quite different traits and further investigation is required before committing significant resources to PAC measurements (Robinson 2015).

5.4.3      Application of CH4:CO2 ratio

Madsen et al. (2010) proposed using the ratio of CH₄:CO₂ in exhaled breath to assess enteric methane production in ruminants. This method requires knowledge about the intake, energy content and heat increment of the ration consumed. Haque et al. (2014) applied this method, using a fixed heat increment factor. Hellwing et al. (2013) regressed open-circuit chamber measurements of DMP in cattle against estimates calculated using CH₄:CO₂ ratios and found them to be only moderately correlated (R² = 0.4), which suggest this method is unsuitable for precision measurements.

5.4.4      Spot sampling with lasers

Spot measurements of methane in the air around cattle’s mouths have been made using laser devices to provide short-term estimates of enteric methane flux (Chagunda et al. 2009; Garnsworthy et al. 2012). These estimates are then scaled up to represent DMP – requiring an impressive number of assumptions to be met to satisfy such scaling. Chagunda and Yan (2011) have claimed correlations of 0.7 between laser and respiratory chamber measurements, but this claim is based on the laser apparatus measuring methane concentrations in the outflow of the chambers, rather than from the animals themselves.

5.5      Emerging and future technologies

5.5.1      Blood methane concentration

This methodology relies on enteric methane being absorbed across the rumen wall, transported in the blood stream to the pulmonary artery and respired by the lungs. The jugular (vein) gas turnover rate of enteric SF₆, (introduced by an intraruminal bolus) and CH₄ has been used to determine the respired concentrations and solubility of these gases (Ramirez-Restrepo et al. 2010). The solubility coefficients and CH₄ concentrations are determined by gas chromatography, comparing the peak area of the sampled gases with standards. Variances in CH₄ and SF₆ blood concentrations may be related to the methodology, or may occur because these gases are not equally re-absorbed. This requires further investigation. Sampling can be logistically challenging and labour intensive and it is important to recognize that this method provides little more than a ‘snapshot’ of methane concentration at time of sampling.

5.5.2      Infrared thermography

Montanholi et al. (2008) have examined the use of infrared thermography as an indicator for heat and methane production in dairy cattle. No direct relationship was reported, however, between temperature in any specific part of the body and methane production.

5.5.3      Intraruminal telemetry

The use of a rumen bolus to measure methane in the liquid phase is logistically possible and small changes (<50 mmol L^-1) in CH₄ concentrations could be detectable (Gibbs 2008). Low pH and redox potential have been correlated with decreased CH₄ concentrations, and a pH and redox sensor has been developed to suit a rumen bolus by eCow Electronic Cow Management at the University of Exeter, UK (www.ecow.co.uk). This technology is still in its exploratory stages but the application of a rumen bolus to measure CH₄ in the rumen headspace has been patented (McSweeney pers. comm.) and could theoretically provide accurate CH₄ concentration estimates for large numbers of free grazing animals.

5.5.4      Quantitative molecular biology

Gibbs (2008) examined the correlation between the numbers of methanogens and CH₄ production in short time intervals. Results from real-time polymerase chain reaction (PCR) suggest that increased CH₄ production is related to increased methanogen metabolic activity rather than increased population size.

Summary

EMP is a complex trait, involving animal physiology and behaviour, plant factors and animal management. Although there are many techniques available to estimate EMP, all have limitations. The appropriateness of a technique is strongly influenced by its intended purpose and the degree of precision required. It is important to recognize that while more sophisticated in vitro techniques can provide robust information about the fermentative, and hence, methanogenic potential of feeds, they do not truly represent in vivo fermentation, nor do they account for feed intake, and will be of limited predictive use for animals grazing heterogeneous pastures. If intake is unknown it will diminish the utility of established models, especially when assumptions regarding ad libitum intake are violated. Lasers, infrared and SF₆ techniques can all be used to measure EMP of animals at pasture. However, all are technically fastidious and in situations where intake is unknown, cannot be used to determine emissions intensity. Respiration chambers, while requiring significant capital to construct and technical skill to operate, provide precise and accurate measurements of EMP on known feed intake. Whilst there are justified criticisms surrounding reproducibility of EMP at pasture and evidence of changed feeding behaviour in some cases, respiration chambers remain the most accurate method of assessing EMP in individual animals.

Author Affiliations

¹John P. Goopy. International Livestock Research Institute. Nairobi, Kenya. email: j.goopy@cgiar.org
²Wageningen University, Animal Nutrition Group, the Netherlands
³CSIRO, Livestock Industries, Queensland 4811, Australia

References

ARC (1980) The nutrient requirements of ruminant livestock. Australian Research Council, CAB International, Wallingford, UK

Berndt A, Boland TM, Deighton MH, Gere JI, Grainger C, Hegarty RS, Iwaasa AD, Koolaard JP, Lasse KR, Luo D, Martin RJ, Martin C, Moate PJ, Molano G, Pinares-Patiño C, Ribaux BE, Swainson NM, WAghorn GC, Williams SRO (2014) Guidelines for use of sulphur hexafluoride (SF 6) tracer technique to measure enteric methane emissions from ruminants. M. G. Lambert, ed. New Zealand Agricultural Greenhouse Gas Research Centre, New Zealand. www.globalresearchalliance.org/app/uploads/2012/03/SF6-Guidelines-all-chapters-web.pdf. Accessed 15 March 2015

Blaxter KL, Clapperton JL (1965) Prediction of the amount of methane produced by ruminants. Brit J Nutr 19:511–22

Blümmel M, Givens DI, Moss AR (2005) Comparison of methane produced by straw fed sheep in open-circuit respiration with methane predicted by fermentation characteristics measured by an in vitro gas procedure. Anim Feed Sci Tech 123–124(Part 1):379–90

Brown D, Cole TJ, Dauncey MJ, Marrs RW, Murgatroyd PR (1984) Analysis of gaseous exchange in open-circuit indirect calorimetry. Med Biol Eng Comput 22:333–338

Chagunda MGG, Ross D, Roberts DJ (2009) On the use of a laser methane detector in dairy cows. Comput Electron Agr 68:157–60

Chagunda MGG, Yan T (2011) Do methane measurements from a laser detector and an indirect open-circuit respiration calorimetric chamber agree sufficiently closely? Anim Feed Sci Tech 165:8–14

Charmley E, Stephens ML, Kennedy PM (2008) Predicting livestock productivity and methane emissions in northern Australia: development of a bio-economic modelling approach. Aust J Exp Agr 48:109–113

Cone JW, Gelder AH van, Visscher GJW, Oudshoorn L (1996) Influence of rumen fluid substrate concentration on fermentation kinetics measured with a fully automated time related gas production apparatus. Anim Feed Sci Tech 61:113–128

Deighton MH, Williams SRO, Hannah MC, Eckard RJ, Boland TM, Wales WJ, Moate PJ (2014) A modified sulphur hexafluoride tracer technique enables accurate determination of enteric methane emissions from ruminants. Anim Feed Sci Tech 197:47–63

Denmead OT (2008) Approaches to measuring fluxes of methane and nitrous oxide between landscapes and the atmosphere. Plant Soil 309:5–24

Dijkstra J, Kebreab E, Bannink A, France J, López S (2005) Application of the gas production technique to feed evaluation systems for ruminants. Anim Feed Sci Tech 123–124:561–578

Ellis JL, Dijkstra J, Kebreab E, Bannink A, Odongo NE, McBride BW, France J (2008) Modelling animal systems paper: aspects of rumen microbiology central to mechanistic modelling of methane production in cattle. J Agr Sci 146:213–233

Ellis JL, Kebreab E, Odongo NE, McBride BW, Okine EK, France J (2007) Prediction of methane production from dairy and beef cattle. J Dairy Sci 90:3456–3467

Fernández C, López MC, Lachica M (2012) Description and function of a mobile open-circuit respirometry system to measure gas exchange in small ruminants. Anim Feed Sci Tech 172:242–246

Flesch TK, Wilson JD, Harper LA, Crenna BP (2005) Estimating gas emission from a farm using an inverse dispersion technique. Atmos Environ 39:4863–4874

Flesch TK, Wilson JD, Harper LA, Crenna BP, Sharpe RR (2004) Deducing ground-to-air emissions from observed trace gas concentrations: a field trial. J Appl Meteorol 43:487–502

Flesch TK, Wilson JD, Harper LA, Todd RW, Cole NA (2007) Determining ammonia emissions from a cattle feedlot with an inverse dispersion technique. Agr Forest Meteorol 144:139–155

Freibauer A (2000) New approach to an inventory of N₂O and CH₄ emissions from agriculture in Western Europe. Kluwer Academic Publishers, Dordrecht–Boston–London.

Gao Z, Desjardins RL, Flesch TK (2010) Assessment of the uncertainty of using an inverse-dispersion technique to measure methane emissions from animals in a barn and in a small pen. Atmos Environ 44:3128–3134

Garnsworthy PC, Craigon J, Hernandez-Medrano JH, Saunders N (2012) On-farm methane measurements during milking correlate with total methane production by individual dairy cows. J Dairy Sci 95:3166–80

Gibbs J (2008) Novel methane assessment in ruminants. Final Report for Project Code: CC MAF POL_2008-37. Ministry of Agriculture and Forestry, Government of New Zealand, Wellington, New Zealand. Accessed March 15 2015

Goopy JP, Donaldson A, Hegarty R, Vercoe PE, Haynes F, Barnett M, Oddy VH (2014b) Low-methane yield sheep have smaller rumens and shorter rumen retention time. Brit J Nutr 111:578–85

Goopy J, Hegarty R (2004) Repeatability of methane production in cattle fed concentrate and forage diets. J Anim Feed Sci 13:75–8

Goopy J, Hegarty R, Robinson D (2009) Two hour chamber measurement provides a useful estimate of daily methane production in sheep. In: Ruminant physiology: digestion, metabolism and effects of nutrition on reproduction and welfare. Proceedings of the XIth International Symposium on Ruminant Physiology, Clermont-Ferrand, France 6–9 Sept 2009, p. 190. Wageningen Academic Pub, The Netherlands

Goopy J, Robinson D, Woodgate R, Donaldson A, Oddy H, Vercoe P, Hegarty R (2015) Estimates of repeatability and heritability of methane production in sheep using portable accumulation chambers. Anim Prod Sci http://dx.doi.org/10.1071/AN13370

Goopy JP, Woodgate R, Donaldson A, Robinson DL, Hegarty RS (2011) Validation of a short-term methane measurement using portable static chambers to estimate daily methane production in sheep. Anim Feed Sci Tech 166–167:219–26

Grainger C, Clarke T, McGinn SM, Auldist MJ, Beauchemin KA, Hannah MC, Waghorn GC, Clark H, Eckard RJ (2007) Methane Emissions from Dairy Cows Measured Using the Sulfur Hexafluoride (SF₆) Tracer and Chamber Techniques. J Dairy Sci 90:2755–2766

Grainger C, Williams R, Clarke T, Wright ADG, Eckard RJ (2010) Supplementation with whole cottonseed causes longterm reduction of methane emissions from lactating dairy cows offered a forage and cereal grain diet. J Dairy Sci 93:2612–2619

Hammond K, Humphries D, Crompton L, Kirton P, Green C, Reynolds C (2013) Methane emissions from growing dairy heifers estimated using an automated head chamber (GreenFeed) compared to respiration chambers or SF₆ techniques. Adv Anim Biosci 4:391

Haque MN, Cornou C, Madsen J (2014) Estimation of methane emission using the CO₂ method from dairy cows fed concentrate with different carbohydrate compositions in automatic milking system. Livest Sci 164:57–66

Hegarty RS (2013) Applicability of short-term emission measurements for on-farm quantification of enteric methane. Animal 7:401–8

Hellwing A, Lund P, Madsen J, Weisberg MR (2013) Comparison of enteric methane production from the CH₄/CO₂ ratio and measured in respiration chambers. Adv Anim Biosci 4:557

Hendricksen R, Minson DJ (1980) The feed intake and grazing behaviour of cattle grazing a crop of Lablab purpureus cv. Rongai. J Agr Sci 95:547–54

Herrero M, Thornton PK, Kruska R, Reid RS (2008) Systems dynamics and the spatial distribution of methane emissions from African domestic ruminants to 2030. Agr Ecosyst Environ 126:122–37

Hungate RE (1966) The rumen and its microbes. Academic Press, New York.

Jamieson WS, Hodgson J (1979) The effects of variation in sward characteristics upon the ingestive behaviour and herbage intake of calves and lambs under a continuous stocking management. Grass Forage Sci 34:273–82

Johnson K, Huyler M, Westberg H, Lamb B, Zimmerman P (1994) Measurement of methane emissions from ruminant livestock using a SF₆ tracer technique. Envir Sci Tech 28:359–362

Johnson KA, Johnson DE (1995) Methane emissions from cattle. J Anim Sci 73:2483–2492

Kempton T, Murray R, Leng R (1976) Methane production and digestibility measures in the grey kangaroo and sheep. Aust J Biol Sci 29:209–214

Klein L, Wright ADG (2006) Construction and operation of open-circuit methane chambers for small ruminants. Aust J Exp Agr 46:1257–1262

Kurihara M, Magner T, Hunter RA, McCrabb GJ (1999) Methane production and energy partition of cattle in the tropics. Brit J Nutr 81:227–234

Laubach J, Kelliher JM (2005) Methane emissions from dairy cows: comparing open-path laser measurements to profile-based techniques. Agr Forest Meteorol 135:340–345

Lockyer DR (1997) Methane emission from grazing sheep and calves. Agr Ecosyst Environ 66:11–18

Lockyer DR, Champion RA (2001) Methane production in sheep in relation to temporal changes in grazing behavior. Agr Ecosyst Environ 86:237–246

Lockyer DR, Jarvis SC (1995) The measurement of methane losses from grazing animals. Environ Pollut 90:383–390

Loh, Z, Chen D, Bai M, Naylor T, Griffith D, Hill J, Denmead T, McGinn S, Edis R (2008) Measurement of greenhouse gas emissions from Australian feedlot beef production using open-path spectroscopy and atmospheric dispersion modelling. Aust J Exp Agr 48:244–247

Loh, Z, Leuning R, Zegelin S, Etheridge D, Bai M, Naylor T, Griffith D (2009) Testing Lagrangian atmospheric dispersion modeling to monitor CO₂ and CH₄ leakage from geosequestration. Atmos Environ 43:2602–2611

Madsen J, Bjerg BS, Hvelplund T, Weisbjerg MR, Lund P (2010) Methane and carbon dioxide ratio in excreted air for quantification of the methane production from ruminants. Livest Sci 129:223–7

McAllister TA, Okine EK, Mathison GW, Cheng KJ (1996) Dietary, environmental and microbiological aspects of methane production in ruminants. Can J Anim Sci 76:231–243

McGinn SM (2006) Measuring greenhouse gas emissions from point sources in agriculture. Can J Soil Sci 86:355–371

McGinn SM, Beauchemin KA, Flesch TK, Coates T (2009) Performance of a dispersion model to estimate methane loss from cattle in pens. J Environ Qual 38:1796–1802

McGinn SM, Chen D, Loh Z, Hill J, Beauchemin KA, Denmead OT (2008) Methane emissions from feedlot cattle in Australia and Canada. Aust J Exp Agr 48:183–185

McGinn SM, Flesch TK, Harper LA, Beauchemin KA (2006) An approach for measuring methane emissions from whole farms. J Environ Qual 35:14–20

Menke KH, Raab L, Salewski A, Steingass H, Fritz D, Schneider W (1979) The estimation of the digestibility and metabolizable energy content of ruminant feeding stuffs from the gas production when they are incubated with rumen liquor in vitro. J Agr Sci 93:217–222

Moate PJ, Deighton MH, Ribaux BE, Hannah MC, Wales WJ, Williams SRO (2015) Michaelis–Menten kinetics predict the rate of SF₆ release from permeation tubes used to estimate methane emissions from ruminants. Anim Feed Sci Tech 200:47–56

Montanholi YR, Odongo NE, Swanson KC, Schenkel FS, McBride BW, Miller SP (2008) Application of infrared thermography as an indicator of heat and methane production and its use in the study of skin temperature in response to physiological events in dairy cattle (Bos taurus). J Therm Biol 33:468–475

Murray PJ, Gill E, Balsdon SL, Jarvis SC (2001) A comparison of methane emissions from sheep grazing pastures with different management intensities. Nutr Cycl Agroecosys 60:93–97

Murray PJ, Moss A, Lockyer DR, Jarvis SC (1999) A comparison of systems for measuring methane emissions from sheep. J Agr Sci 133:439–444

Nay SM, Mattson KG, Bormann BT (1994) Biases of chamber methods for measuring soil CO₂ efflux demonstrated with a laboratory apparatus. Ecology 75:2460–2463

Odongo NE, Alzahal O, Las JE, Kramer A, Kerrigan B, Kebreab E, France J, McBride BW (2007) Development of a mobile open-circuit ventilated hood system for measuring real-time gaseous emissions in cattle. CABI Publishing, Wallingford, UK.

Payne RW, Murray DA, Harding SA (2011) An introduction to the GenStat Command Language (14th Edition). VSN International, Hemel Hempstead, UK

Pell AN, Schofield P (1993) Computerized monitoring of gas production to measure forage digestion in vitro. J Dairy Sci 76:1063–1073

Pinares C, Waghorn G (2014) Technical Manual on Respiration Chamber Designs. New Zealand Ministry of Agriculture and Forestry, Wellington NZ. Accessed March 15, 2015

Pinares-Patiño CS, Hour PD, Jouany JP, Martin C (2007) Effects of stocking rate on methane and carbon dioxide emissions from grazing cattle. Agr Ecosyst Environ 121:30–46

Pinares-Patiño CS, Lassey KR, Martin RJ, Molano G, Fernandez M, MacLean S, Sandoval E, Luo D, Clark H (2011) Assessment of the sulphur hexafluoride (SF₆) tracer technique using respiration chambers for estimation of methane emissions from sheep. Anim Feed Sci Tech 166:201–209

Place SE, Pan Y, Zhao Y, Mitloehner FM (2011) Construction and operation of a ventilated hood system for measuring greenhouse gas and volatile organic compound emissions from cattle. Animal 1:433–446

Ramirez-Restrepo CA, Barr TN, Marriner A, López-Villalobos N, McWilliam EL, Lassey KR, Clark H (2010) Effects of grazing willow fodder blocks upon methane production and blood composition in young sheep. Anim Feed Sci Tech 155:33–43

Robinson D, Goopy J, Donaldson A, Woodgate R, Oddy V, Hegarty R (2014) Sire and liveweight affect feed intake and methane emissions of sheep confined in respiration chambers. Animal 8:1935–1944

Robinson DL, Goopy JP, Hegarty RS, Oddy VH (2015) Comparison of repeated measurements of CH4 production in sheep over 5 years and a range of measurement protocols. J Anim Sci submitted

Suzuki T, McCrabb GJ, Nishida T, Indramanee S, Kurihara M (2007) Construction and operation of ventilated hood-type respiration calorimeters for in vivo measurement of methane production and energy partition in ruminants. Springer, The Netherlands

Suzuki T, Phaowphaisal I, Pholson P, Narmsilee R, Indramanee S, Nitipot T, Haokaur A, Sommar K, Khotprom N, Panichpol V, Nishida T (2008) In vivo nutritive value of pangola grass (Digitaria eriantha) hay by a novel indirect calorimeter with a ventilated hood in Thailand. Jarq-Jpn Agr Res Q 42:123–129

Takahashi J, Chaudhry AS, Beneke RG, Young BA (1999) An open-circuit hood system for gaseous exchange measurements in small ruminants. Small Ruminant Res 32:31–36

Theodorou MK, Williams BA, Dhanoa MS, McAllan AB, France J (1994) A simple gas production method using a pressure transducer to determine the fermentation kinetics of ruminant feeds. Anim Feed Sci Tech 48:185–197

Tomkins NW, McGinn SM, Turner DA, Charmley E (2011) Comparison of open-circuit respiration chambers with a micrometeorological method for determining methane emissions from beef cattle grazing a tropical pasture. Anim Feed Sci Tech 166-167:240–247

Turner HG, Thornton RF (1966) A respiration chamber for cattle. Aust Soc Anim Prod 6:413–419

Williams SRO, Moate PJ, Hannah MC, Ribaux BE, Wales WJ, Eckard RJ (2011) Background matters with the SF₆ tracer method for estimating enteric methane emissions from dairy cows: A critical evaluation of the SF₆ procedure. Anim Feed Sci Tech170:265–276

Yan T, Porter MG, Mayne CS (2009) Prediction of methane emission from beef cattle using data measured in indirect open-circuit respiration calorimeters. Animal 3:1455–1462

Zimmerman PR, Zimmerman RS (2012) Method and system for monitoring and reducing ruminant methane production. United States Patent number US20090288606 A1