1
Options for the abatement of methane and nitrous oxide from ruminant
production – a review
R.J. Eckard1,2#, C. Grainger2 & C.A.M. de Klein3
1
University of Melbourne, Parkville, Victoria 3010, Australia
Department of Primary Industries, 1301 Hazeldean Road, Ellinbank, 3821, Victoria, AUSTRALIA
3
AgResearch Invermay, Private Bag 50034, Mosgiel, New Zealand
2
Abstract
Agriculture produces ~10-12 % of total global anthropogenic greenhouse gas emissions, contributing
~50% and ~60% of all anthropogenic methane (CH4) and nitrous oxide (N2O), respectively. Apart from their
significant contribution to anthropogenic greenhouse gas emissions, the energy lost as CH4 and total N losses
are two of the most significant inefficiencies remaining in ruminant production systems. A number of
options are reviewed for reducing enteric CH4 and N2O production from ruminant production systems,
mainly focused around breeding, feeding, animal management, soil and fertiliser management and rumen
manipulation. In order to fully assess the net abatement potential, each strategy needs to be subjected to
whole farm systems modelling and a full life cycle assessment, to ensure that a reduction in emissions at one
point does not stimulate higher emissions elsewhere in the production system. Most of the options reviewed
require many years of research before practical options and commercially viable products are available for
implementation on farm. This paper reviews the options for livestock production to reduce CH4 and N2O
emissions, while further improving production, highlighting research issues and the need for a systems
approach to the evaluation of the relative merits of abatement options.
Keywords: Enteric, nitrogen, fertiliser, dung, urine, greenhouse gas, mitigation
#
Corresponding author. Email: rjeckard@unimelb.edu.au
Introduction
Agriculture produces ~10-12 % of total global anthropogenic greenhouse gas emissions, contributing
~50% and ~60% of all anthropogenic methane (CH4) and nitrous oxide (N2O), respectively (Smith et al.
2007). Both CH4 and N2O are powerful greenhouse gasses, with global warming potentials of 21 (CH4) and
310 (N2O) currently used for reporting emissions under the Kyoto Protocol; although there is debate over the
specific global warming potentials that should be used (Forster et al. 2007).
Apart from their contribution to anthropogenic greenhouse gas emissions, energy and N losses are two
of the most significant inefficiencies in ruminant production systems. Thus the challenge for research is to
develop technologies and strategies to improve the efficiency of the energy and N cycles in ruminant
production, leading to more efficient and sustainable production systems for the future.
Several reviews of enteric CH4 and N2O production and mitigation have recently been published
(Beauchemin et al. 2008; Dalal et al. 2003; de Klein & Eckard 2008; McAllister & Newbold 2008). This
paper therefore aims only to summarise the current state of knowledge as relevant to ruminant production
systems, highlighting future research needs and directions.
Enteric Methane
Globally, ruminant livestock produce ∼80 million tonnes of CH4 annually accounting for ∼33% of
anthropogenic emissions of CH4 (Beauchemin et al. 2008). Enteric CH4 is produced under anaerobic
conditions in the rumen, by methanogenic Archaea, utilising CO2 and H2 to form CH4, thus reducing
metabolic H2 produced during microbial metabolism (McAllister & Newbold 2008). If H2 accumulates, reoxidation of NADH is inhibited, inhibiting microbial growth, forage digestion and the associated production
of acetate, propionate and butyrate (Joblin 1999). Thus any mitigation strategy aimed at reducing
methanogen populations must include an alternative pathway for H2 removal from the rumen as well.
With an energy content of 55.22 MJ/kg (Brouwer 1965) CH4 represents a significant loss of dietary
energy from the production system (Table 1). Typically, about 6 to 10% of the total gross energy consumed
by the dairy cow is converted to CH4 and released via the breath. Thus reducing enteric CH4 production may
2
also lead to production benefits. Figure 1 presents a summary of the main options for reducing enteric N2O
production; these are reviewed below.
Table 1. Typical ranges in CH4 emissions from three classes of ruminant, energy lost as CH4, with an
estimate of effective annual grazing days lost
a
b
c
d
Animal Class
Average
CH4
MJ CH4 lost
Average Daily
Effective
Liveweight
(kg/hd/year)
/hd/day
Energy
annual grazing
(kg)
requirement
days lost
(MJ/hd/day)
Mature ewe
48
10 to 13
1.5 to 2.0
13.0
43 to 55
Beef steer
470
50 to 90
7.6 to 13.6
83
33 to 60
Lactating dairy cow
550
91 to 146
13.6 to 22.1
203
25 to 40
a
Data drawn from studies reviewed below.
b
Assuming an energy density of 55.22 MJ/kg CH4 (Brouwer 1965)
d
Effective annual grazing days lost = c Daily Requirement/ b Energy lost x 365.25
c
(Standing Committee on Agriculture 1990)
Animal manipulation
A number of experiments have reported variation between animals in CH4 emissions per unit of feed
intake. In a trial involving 302 grazing dairy cows mean CH4 emissions of 19.3 ±2.9 g/kg DMI were reported
(Clark et al. 2005); the 15% variance suggesting heritable differences in methanogenesis. Similar responses
were reported in sheep on an unlimited pasture diet (Pinares-Patiño et al. 2003). However, while (Hegarty et
al. 2007) also reported a significant (P = 0.01) positive relationship between CH4 production and net feed
intake (NFI) in Angus steers (slope of 13.38), this explained only a small proportion of the observed
variation in CH4, perhaps indicating a genotype x nutrition interaction. These data suggest that animal
breeding could achieve a 10 to 20% reduction in CH4 losses from DM during digestion (Waghorn et al.
2006). However, breeding for reduced methanogenesis is unlikely to be compatible with other competing
breeding objectives. In contrast, breeding for improved feed conversion efficiency (lower NFI) should be
compatible with existing breeding objectives and likely to both reduce CH4 and the ratio of CH4 per unit of
product produced.
Reducing the number of unproductive animals on farm has potential to both improve profitability and
reduce CH4. Strategies like extended lactation in dairying, where cows calve every 18 months rather than
annually, reduces herd energy demand by 10.4% (Trapnell & Malcolm 2006) and thus potentially reduces
on-farm CH4 emissions by a similar amount (Smith et al. 2007). Through earlier finishing of beef cattle in
feedlots, slaughter weights are achieved at a younger age, with reduced lifetime emissions per animal and
thus proportionately less animals producing CH4 (Smith et al. 2007).
Kangaroos produce negligible amounts of CH4 in their foregut (Hackstein & Van Alen 1996; Kempton
et al. 1976), with PCR assays unable to detect Archaea in the foregut contents of two species in Australia
(Ouwerkerk et al. 2005). However, kangaroos are also known for high quality, low fat, meat potentially
providing countries like Australia with up to 27% CH4 abatement potential for the same total meat
production (Wilson & Edwards 2008), notwithstanding likely consumer resistance.
A number of options therefore exist to either breed ruminants with lower CH4 production, to minimise
unproductive animal numbers on-farm and possibly shift to more novel production systems, all of which
have potential to both reduce total CH4 emissions and improve on-farm profitability.
Dietary Manipulation
Forage quality
Improving forage quality, either through feeding forages with lower fibre and higher soluble
carbohydrates, changing from C4 to C3 grasses, or even grazing less mature pastures can reduce CH4
production (Beauchemin et al. 2008; Ulyatt et al. 2002). Methane production per unit of cellulose digested
has been shown to be three times that of hemicellulose (Moe & Tyrrell 1979), while cellulose and
hemicellulose ferment at a slower rate than non-structural carbohydrate, thus yielding more CH4 per unit of
substrate digested (McAllister et al. 1996). Consequently, adding grain to a forage diet increases starch and
reduces fibre intake reducing rumen pH and favouring the production of propionate rather than acetate in the
3
rumen (McAllister & Newbold 2008). Improving forage quality also tends to increase voluntary intake and
reduces retention time in the rumen, promoting energetically more efficient post-ruminal digestion and
reducing the proportion of dietary energy converted to CH4 (Blaxter & Clapperton 1965). Methane emissions
are also commonly lower with higher proportions of forage legumes in the diet, partly due to lower fibre
contact, faster rate of passage and in some case the presence of condensed tannins (Beauchemin et al. 2008).
Improving diet quality can both improve animal performance and reduce CH4 production, but also
improve efficiency by reducing CH4 emissions per unit of animal product. Plant breeding therefore offers
potential to improve digestibility as well as reduce CH4. However, many of these strategies may also lead to
increased DM intake per animal, or may also provide the farmer with an opportunity to increase stocking
rate, resulting in either no net change or even a net increase in CH4 production. Likewise, adding more grain
to the diet will incur additional N2O and transport emissions from the grain production. Further research and
modelling is therefore required to understand likely the relationships between improving diet quality and
voluntary intake, stocking rate and net CH4 production, for a range of production systems.
Plant secondary compounds
Condensed tannins (CT) have been shown to reduce CH4 production by 13 to 16% (DMI basis)
(Carulla et al. 2005; Grainger et al. 2009; Waghorn et al. 2002; Woodward et al. 2004), mainly through a
direct toxic effect on methanogens. However, high CT concentrations (>55 g CT/kg DM) may reduce
voluntary feed intake and digestibility (Beauchemin et al. 2008; Grainger et al. 2009; Min et al. 2003). Plant
saponins also hold potential to reduce CH4, some saponin sources clearly more effective than others, with
CH4 suppression attributed to their anti-protozoal properties (Beauchemin et al. 2008).
In reviewing 17 studies with beef, sheep and dairy cattle (Beauchemin et al. 2008) concluded that for
every 1% (DMI basis) increase in fat in the diet, CH4 (g/kg DMI) was reduced by 5.6%. Assuming that most
forages have some fat content, and that DMI may be suppressed at fat intakes above 6 to 7%, CH4
abatements of 10–25% are possible from the addition of dietary oils to the diet of ruminants (Beauchemin et
al. 2008). There are five possible mechanisms by which lipid supplementation reduces CH4: reducing fibre
digestion (mainly in long chain fatty acids); lowering DMI (if total dietary fat exceeds 6-7%); suppression of
methanogens (mainly in medium chain fatty acids); suppression of rumen protozoa, and to a limited extent
through biohydrogenation (Beauchemin et al. 2008; Johnson & Johnson 1995; McGinn et al. 2004).
While extracts of CT and saponins may be commercially available, their cost is currently prohibitive
for routine use in ruminant production systems. On the other hand a number of high-oil by-products are
already used as stock feeds at cost-effective prices. Plant breeding or genetic manipulation offers potential to
increase concentrations of oils and CT in forages where direct supplementation may be limited. In particular,
having elucidated the biosynthetic pathway of the Omega-3 polyunsaturated fatty acid, eicosapentanoic acid,
(Sayanova & Napier 2004) raise the prospect of producing this in transgenic plants. Further research is,
however, still required on the optimum sources, types of oil, level of CT astringency (chemical composition),
plus the feeding methods and dose rates required to reduce CH4 and stimulate production.
Dietary supplements
Dietary supplements offer potential to profitably reduce CH4 emissions from intensive ruminant
production systems, with many strategies already available for implementation on-farm. Yeast cultures of
Saccharomyces cerevisiae potentially stimulate acetogenic microbes in the rumen, consuming H2 to form
acetate (Chaucheyras et al. 1995), thus potentially reducing CH4 production. However, results appear to be
strain dependent (Newbold et al. 1996) and variable in their impact on CH4 production in the rumen
(McGinn et al. 2004). Enzymes in the form of cellulases and hemicellulases, added to the diet of ruminants,
have been shown to improve ruminal fibre digestion and productivity (Beauchemin et al. 2003) and, perhaps
through reducing the acetate-to-propionate ratio, reduced CH4 by 28% in vivo and 9% in vivo (Beauchemin
et al. 2008). These enzymes are widely used in the food processing, textile and paper industries, with
potential for large quantities to be available at reasonable cost. Further research is still required to screen a
large number of yeast strains and enzymes to isolate those with both a production benefit and significant CH4
abatement potential.
Dicarboxylic acids, like fumarate, malate and acrylate, are precursors to propionate production in the
rumen and can act as an alternative H2 sink restricting methanogenesis. (McAllister & Newbold 2008)
reviewed studies showing between 0 and 75% reductions in CH4 from feeding fumaric acid. However, at the
4
relatively high dose rates required, dicarboxylic acids would be prohibitively expensive as an abatement
strategy.
Rumen Manipulation
Manipulating microbial populations in the rumen, through chemical means, by introducing
competitive or predatory microbes, or through vaccination approaches, can reduce CH4 production. A
preliminary study in Australia suggested that vaccination against methanogens may reduce methanogenesis,
reporting a 7.7% (DMI basis) reduction in CH4, although results were not repeatable with subsequent vaccine
preparations (Wright et al. 2004). Methanogen populations in the rumen may be influenced by diet and
geographic location (Wright et al. 2007), increasing the challenge for developing a broad-spectrum
methanogen vaccine. Development of a vaccine against cell-surface proteins, common to a broad range of
methanogen species may improve the efficacy of vaccination as a CH4 mitigation strategy (McAllister &
Newbold 2008). Biological control strategies such as bacteriophages or bacteriocins could prove effective for
directly inhibiting methanogens and redirecting H2 to other reductive rumen bacteria such as propionateproducers or acetogens (McAllister & Newbold 2008). However, most of these options are in the early stages
of investigation and still require significant research over an extended period to deliver commercially viable
vaccines and biological control options that will be effective over a range of production systems and regions.
Reductive acetogenesis has been suggested as an alternative to methanogenesis utilising H2 and CO2 to
form acetate as a source of energy rather than CH4 (Joblin 1999). However, methanogens effectively outcompete acetogens for H2 in the rumen, with the reduction of CO2 to acetate thermodynamically less
favourable than reduction of CO2 to CH4 (McAllister & Newbold 2008). If CH4 was wholly replaced by
acetate in ruminants this could represent an energetic gain of 4 - 15% to the animal (Joblin 1999) and, where
methanogenesis is inhibited, reductive acetogenesis can be increased in ruminal fluid with a possible energy
gain of about 13 – 15% (Nollet et al. 1997). Research on acetogenesis as a CH4 abatement option is still
largely conceptual to date with extensive research still required to understand the physiology and ecology of
acetogens, and their relative dominance is some environments (eg. Kangaroo fore stomach) but not in the
rumen.
Halogenated analogues like bromochloromethane (BCM) and chloroform are potent inhibitors of CH4
formation in ruminants, with BCM reducing CH4 emissions by 57, 84 and 91% (DMI basis) in feedlot steers,
with increasing dose rate (Tomkins & Hunter 2003). Reducing protozoal numbers chemically has been
shown to reduce CH4 by up to 26% (DMI basis), as methanogens are often attached to the surface of, or are
endosymbionts within, rumen ciliate protozoa (McAllister & Newbold 2008). However, the effectiveness of
these chemicals is transitory and their to animal diets is unlikely to gain public acceptability.
Monensin is a polyether ionophore antibiotic that decreases the acetate-to-propionate ratio in the
rumen, effectively decreasing CH4 production. The effect of monensin on lowering CH4 production appears
to be dose-dependent, with lower doses (10-15 ppm) producing a profitable milk response but showing no
effect on CH4 (Grainger et al. 2008; Waghorn et al. 2008), but with higher doses (24 to 35 ppm) (McGinn et
al. 2004; Sauer et al. 1998; Van Vugt et al. 2005) reducing CH4 production by up to 10% (g/kg DMI).
However, there have been questions over the persistence of CH4 suppression (Johnson & Johnson 1995),
plus questions over the future use of antibiotics in animal production systems (Eckard et al. 2000).
Nitrous Oxide
Nitrous oxide emissions account for ∼10% of global greenhouse gas emissions, with ∼90% of these
emissions derived from agricultural practices (Smith et al. 2007). Nitrous oxide in soils is produced largely
by the microbial process of denitrification and to a lesser extent through nitrification. Nitrification is an
aerobic process that oxidises ammonium (NH4+) to nitrate (NO3−) with N2O a by-product, while dissimilatory
nitrate reduction (denitrification) is an anaerobic process that reduces NO3− into N2, with N2O an obligatory
intermediate (de Klein & Eckard 2008). While field measurements indicated that high N2O emission rates
generally coincide with soil conditions that are conducive to denitrification (anaerobic, good NO3− supply),
nitrification is often an essential prerequisite for converting urine and N fertilisers inputs into soil NO3− (de
Klein & Eckard 2008).
Nitrous oxide emissions are moderated by temperature, water-filled pore space (as a surrogate of
anaerobicity), available soil carbon, soil pH and soil nitrate (Whitehead 1995). However, soil NO3− levels
and soil aeration are likely to be the key factors affecting N2O emissions from grazing systems (Eckard et al.
5
2003). Thus strategies for improving the efficiency of N cycling in animal production systems, and
improving soil aeration, should also lead to lower N2O emissions. Figure 2 presents a summary of the main
options for reducing enteric N2O production; these are reviewed below.
Animals
Ruminants excrete between 75 and 95% of the N they ingest, with excess dietary N increasingly
excreted in the urine, while dung N excretion remains relatively constant (Castillo et al. 2000; Eckard et al.
2007). Of the dietary N consumed by ruminants, <30% is utilised for production, with >60% being lost from
the grazing system (Whitehead 1995). The effective N application rate within a urine patch from a dairy cow
is commonly between 800 and 1300 kg N/ha (Eckard et al. 2006b), depositing N at concentrations orders of
magnitude greater than soil-plant systems can efficiently utilise. Strategies for reducing N2O emissions
should therefore also focus on improving the efficiency of N cycling through the soil-plant-animal system.
Conceptually, if animal urine in grazing systems was spread more evenly across the paddock the
effective N application rate will be reduced, potentially reducing N2O emissions. While no specific animal
technologies are currently developed, this may require some physical intervention on the animal, yet to be
practically and ethically conceived, that will distribute the urine more evenly (de Klein & Eckard 2008).
Breeding and diet
Genetic manipulation or breeding of animals may provide improvements in the N conversion
efficiency within the rumen, animals that urinate more frequently or animals that walk while urinating, all
leading to lower N concentrations or greater spread of urine (de Klein & Eckard 2008). (Coffey 1996)
reported that an improvement in feed conversion efficiency of 0.01 could result in a 3.3% reduction in
nutrient excretion, assuming similar growth rate and nutrient retention. Breeding animals for increased feed
conversion efficiency should therefore lead to animals that partition more of their intake to production and
less to N excretion, thereby reducing potential N2O losses.
Ruminants on lush spring pasture commonly ingest protein in excess of requirement, but are usually
energy limited, resulting in higher ruminal ammonia concentrations being excreted in the urine as urea
(Whitehead 1995). Balancing protein-to-energy ratios in the diet of ruminants is therefore important to
minimise N2O emissions resulting from excess urinary N excretion. (Misselbrook et al. 2005) showed that
dairy cows fed on a 14% CP diet excreted 45% less urinary N than dairy cows on a 19% CP diet. Similarly,
(van Vuuren et al. 1993) showed that supplementing cows on a perennial ryegrass diet with low protein/high
sugar supplements reduced the amount of total N and urine N excreted by 6–9% and 10–20%, respectively,
compared with an all-grass diet. More recently, Miller et al. (2001) found that dairy cows on a novel ‘high
sugar’ variety of perennial ryegrass excreted 18% less N in total and 29% less urine N.
Improving N efficiency and reducing excess urinary N can be achieved through either breeding
animals with improved N efficiency, breeding forages that utilise more N more efficiently, plus have a
higher energy to protein ratio, or balancing high protein forages with high energy supplements.
Tannins
Condensed tannins (CT) complex with proteins in the rumen protecting them from microbial
digestion, resulting in either more efficient digestion of amino acids in the abomasum and lower intestine, or
the CT-protein complex being excreted in the dung (de Klein & Eckard 2008; Min et al. 2003). Carulla et al.
(2005) showed that sheep fed a CT extract from Acacia mearnsii (black wattle) increased their partitioning
of N from urine to faeces, reducing urinary N by 9.3% as a proportion of total N excreted. (Grainger et al.
2009) added a CT extract from black wattle to the diet of lactating dairy cattle and showed a 45 to 59%
reduction in urinary N excretion, with 18 to 21% more N in faeces. Likewise, (Misselbrook et al. 2005)
showed that dairy cows on a 3.5% CT diet excreted 25% less urine N, 60% more dung N, and 8% more N
overall, compared with cows on a 1% CT diet.
Faecal N is mainly in organic form and thus less volatile, whereas urinary N is largely urea and thus
more rapidly nitrified to NO3- and, apart from being vulnerable to leaching, can account for about 60% of
N2O emissions from pasture (de Klein & Ledgard 2005). In addition, the CT-protein complex in dung is
more recalcitrant in the soil, as mineralization of the complex is inhibited and decomposes more slowly than
faeces that do not contain CT (Fox et al. 1990; Niezen et al. 2002; Palm & Sanchez 1991; Somda & Powell
6
1998). By reducing N excretion in the urine, the risk of subsequent N2O emission from this highly
concentrated N source is reduced (de Klein & Eckard 2008).
Currently CT extracts are prohibitively expensive as there is no large commercial demand for their
production in agriculture. As many forage plants contain CT plant breeding could present an option to
introduce CT into the diet of animals where daily supplementation is not practical of economic. Further
research is, however, required to identify suitable and cost-effective high-tannin forages and tannin extracts
for supplementing the diet of ruminants.
Salt supplementation increases water intake in ruminants, reducing both urinary N concentration and
inducing more frequent urination events, thus spreading urinary N more evenly across grazed pasture
(Ledgard et al. 2007b). In a laboratory study, (van Groenigen et al. 2005) found that decreasing the N
concentration of urine tended to decrease N2O emissions from incubated soil cores by 5-10%. However, no
field measurements of actual N2O emissions have been reported in association with breeding or salt
supplementation, and this field requires further research.
Soils
Fertiliser and effluent inputs
The rate, source and timing of N fertiliser applications are important management factors affecting
the efficiency of pasture growth responses, and thus potential N2O losses. When conditions are suitable for
denitrification, N2O emissions increase exponentially with the rate of N applied in any single application
(Eckard et al. 2006a; Mosier et al. 1983; Whitehead 1995). In a modelling study (Eckard et al. 2006b)
predicted annual N2O emissions to increase exponentially as the annual rate of N fertiliser was increased,
with increasing separation between the two N fertiliser sources modelled. (Galbally et al. 2005) reported
N2O emissions of 1.0–1.2 kg N2O -N/ha per year from unfertilised irrigated dairy pastures in temperate
Australia, increasing to 2.4 kg N2O -N/ha per year from three applications of 50 kg N/ha per year.
Nitrate-based N fertiliser has been shown to result in high N2O emissions, relative to ammoniated-N
sources, when applied to actively growing pasture. In a recent review, (de Klein et al. 2001) quoted N2O
emission factors of <0.1–1.9% (median 0.5%), from N applied as urea fertiliser, and<0.1–12% (median
3.2%) from N applied as calcium nitrate. Similarly, (Eckard et al. 2003) reported 12.9% average higher N2O
losses from the use of ammonium nitrate relative to urea. In South Africa, Australia and New Zealand urea
or di-ammonium phosphate is the main source of N applied to intensive pastures, with recommended rates
not exceeding 50–60 kg fertiliser N per hectare in any single application per grazing rotation (Eckard 1989;
1990; Eckard et al. 1995; Eckard & Franks 1998; Ledgard 1986). Apart from reducing the total amount of N
fertiliser used and perhaps optimising the timing of application in relation to soil moisture conditions, further
N2O abatement potential in the rate and source of N fertiliser application may be limited in pasture-based
grazing systems.
The rate, timing and placement of animal effluent applied to soils all affect potential N2O emissions.
The N2O emissions from effluent applied to soils are generally lower than from urine patches, provided the
effluent is applied at recommended rates and at appropriate times of the year (Chadwick 1997; de Klein et al.
2001; Saggar et al. 2004). (Saggar et al. 2004) indicated that N2O emissions from effluent were higher when
applied to wet soil compared with drier soil, and that emission peaks generally occurred within 24 h of
application. The timing of effluent application in relation to N fertiliser application can also affect N2O
emissions, with N2O emissions being lower when N fertiliser was applied at least 3 days after the effluent,
rather than together with the effluent (Stevens & Laughlin 2002).
Effluent application techniques can also affect N2O emissions. For example, injection or
incorporation of effluent into the soil could increase the direct N2O emission but reduce ammonia (NH3)
volatilisation (Chadwick 1997; Saggar et al. 2004), resulting in lower indirect N2O emissions. In addition,
effluent injection is likely to increase the overall N use efficiency of effluent and could thus reduce N
fertiliser requirement and the associated N2O emissions (Chadwick 1997).
Nitrification Inhibitors
Nitrification inhibitors are chemical compounds that inhibit the oxidation of NH4+ to NO3− in soils
and thus reduce N2O emissions from NH4+-based fertilisers or from urine (Di & Cameron 2002). The most
widely used are nitrapyrin and dicyandiamide (DCD) (de Klein & Eckard 2008). Nitrification inhibitorcoated fertilisers have been shown to be effective in reducing nitrification, and N2O emissions by up to
7
∼80%, as reviewed by (de Klein et al. 2001). Applied as a spray, nitrification inhibitors can also be effective
in reducing N2O emissions from animal urine by 61–91%, with pasture yield increases of 0–36% (Di et al.
2007; Kelly et al. 2008; Smith et al. 2008). However, many of these studies have been conducted under
optimal conditions for N2O production and measured over short periods, with on-farm abatement potentials
likely to be more conservative than published data (de Klein & Eckard 2008).
Novel approaches to placing nitrification inhibitors where they are most needed, could include either
feeding inhibitors to animals, with the inhibitor excreted in the urinary stream, or breeding plants that exude
natural inhibitors from their roots. (Ledgard et al. 2007a) demonstrated that ruminants supplemented with a
nitrification inhibitor (DCD) excreted the inhibitor unaltered in the urine. Further research is still required to
quantify the N2O abatement potential of this approach, including a slow-release delivery mechanism, as this
has large potential for N2O abatement from urine in grazing systems. Recently, (Subbarao et al. 2006)
reported on the release of a natural nitrification inhibitor from the roots of Brachiaria humidicola, raising the
prospect of breeding plants that synthesise their own inhibitors.
Apart from directly reducing N inputs into grazing systems, nitrification inhibitors are currently the
only well published technology available for reducing the loss of N from soils. While their use has
historically been restricted mainly due to cost, with future emissions constraints envisaged in many
countries, they are likely to form a significant part of any comprehensive abatement strategy for reducing
N2O emissions from both urinary and N fertiliser inputs into pasture systems.
Grazing Management
Restricting grazing on seasonally wet soils not only reduces N inputs from urine, but also reduces
hoof compaction of the soil which contributes to increased soil anaerobicity. (Luo et al. 2008) and (de Klein
et al. 2006) reported a total reduction in direct and indirect N2O emissions from the farm system of 7–11%,
under restricted grazing regimes in the wetter months, following subsequent land application of effluent from
feed or stand-off pads, as opposed to conventional grazing. (Schils et al. 2006) reported that due to the
combined effect of reduced N fertiliser use and reduced grazing time on case study farms in The
Netherlands, N2O emissions were reduced by ∼10% from the total farm system. These studies show that
increasing N utilisation increases N efficiency and reduces N losses while increasing production.
Irrigation and drainage
(Phillips et al. 2007) measured N2O fluxes from adjacent flood irrigated dairy pasture bays, using a
micrometeorological method, showing N2O emissions rising rapidly 2-3 days after flood irrigation, when soil
water filled pore space (WFPS) was >~95%, and remaining high for 1-2 days before gradually decreasing to
background levels thereafter as soil moisture decreased. The low N2O emissions immediately following
irrigation were most likely due to complete denitrification producing mainly N2 emissions (Phillips et al.
2007). Irrigation through extended dry seasons may in fact reduce N2O emissions in a later wetter season by
reducing the build up of unutilised soil NO3- through increased plant uptake (Jordan & Smith 1985).
As denitrification is enhanced under conditions of low soil aeration reducing water-logging of pastures
will reduce N2O emission potential. A common practice in the management of seasonally wet soils has been
to introduce surface or subsurface drains, but the impact of this management practice on N2O emissions is
not straightforward. Waterlogged soils will denitrify more than well drained soils but improved drainage will
increase N loss through drains only to denitrify in a wetland or sump elsewhere in the landscape (de Klein &
Eckard 2008). However, if the improved drainage merely moves the WFPS of the soil below saturation
(±80%), but remains above wilting point (40%), this may actually increase N2O emissions (Granli &
Bøckman 1994) and could lead to increased nitrate leaching. In some cases stimulating denitrification has
been recommended as a means of reducing nitrate leaching in nitrate sensitive areas (Russelle et al. 2005).
These data highlight the need for further research on the compromise between managing irrigation for
efficient plant growth versus N2O emissions, as well as the compromise between improving drainage and
enhanced NO3- leaching, for a range of soil, system and environmental objectives.
Conflicting and complementary strategies
An important component of the research into mitigation options is whole farm system modelling and
life cycle assessment (LCA; ISO 14040 series). This is critical to firstly assess the likely whole farm impacts,
but also to ensure that the strategy does not increase emissions elsewhere in the production chain. For
8
example, improving pasture quality (digestibility) may reduce CH4 emissions, but is also likely to increase
DM intake. With improved pasture quality a logical response by the farmer is also to increase stocking rate.
These assumptions were modelled using DairyMod (Johnson et al. 2008), a mechanistic whole farm systems
model, comparing the impact of low quality (60% digestibility, 9.6 MJ ME/kg, 25% CP) versus high quality
(67% digestibility, 10.8 MJ ME/kg, 27% CP) diets. The simulation allowed the model to adjust stocking rate
to achieve a constant pasture utilisation. Under the higher quality pasture system, the model predicted a 33%
increase in stocking rate, a 38% increase in milk/ha and 19% less total CO2e/L milk, 11% less CH4/cow but
26% more CH4/ha. This modelling clearly shows that improving pasture quality may well improve
productivity, as well as lower emissions intensity per unit of product produced, but the farms total
greenhouse footprint was also increased. This understanding is important for producers potentially facing
emissions constraints (eg. Australia and New Zealand).
Using algorithms from the Australian National Greenhouse Gas Inventory, built into a simple
spreadsheet, (Eckard et al. 2002) estimated that an average dairy farm in southern Australia emits ~72% of
emissions as CH4, with ~14% of N2O from urine deposition, either directly or indirectly. Assuming a
nitrification inhibitor was sprayed on the pastures achieving between 61 and 91% less N2O loss from urine,
this would translate into a whole farm abatement of between 8.4 and 12.5%. If the inhibitor resulted in 25%
more pasture growth, the options would be to either increase stocking rate or reduce N fertiliser inputs. With
a 25% increase in stocking rate total farm emissions would be 11.5 and 7.6% higher than prior to application.
In contrast, reducing N fertiliser inputs by 25%, assuming improved N conservation in the soil due to the
inhibitor, would result in 12.0 and 16.2% less total farm emissions. This calculation demonstrates the need to
understand the full context for achieving a net whole farm systems abatement prior to promoting strategies to
the farming community.
While not all the strategies reviewed are directly additive, where strategies act at different points in the
system, their cumulative impact on total emissions from a production system can be significant. For
example, dairy cattle bred for improved feed conversion efficiency (10% less CH4), fed on dietary oils (10%
less CH4), milked on an extended lactation management system (10% less CH4), with a nitrification inhibitor
sprayed on the paddocks twice per year (61% less N2O) could feasibly add to a cumulative emission
reduction of 40% less whole farm greenhouse gas emissions, but also significantly improved production
from the farm.
Conclusions
A number of abatement options have been identified, that can be implemented in animal production
systems in the immediate or near future, many of which are likely to be cost-effective in their own right.
However, most of the options reviewed require many years of research before practical and commercially
viable products and options are available for implementation on farm. In addition, it is clear that most of the
options currently available are more suited to more intensive animal production (eg. feeding supplements and
additives, nitrification inhibitors), with far fewer options available for more extensive grazing systems. In
addition, very few of these abatement strategies have been subjected to a comprehensive LCA and modelling
of whole farm systems emissions; an important step in evaluating these complex interactions that are likely
to occur, before recommending strategies to farmers that will resulting in a meaningful net reduction in
greenhouse gas emissions.
Acknowledgements
The authors have drawn heavily on a series of papers presented at the 3rd International Greenhouse in
Animal Agriculture Conference, published in the Australian Journal of Experimental Agriculture volume 48.
In particular the recent review of Karen Beauchemin, Michael Kreuzer, Tim McAllister, Jamie Newbold and
Frank O'Mara, are duly acknowledged as key sources of information.
References
Beauchemin, K.A., Colombatto, D., Morgavi, D.P. & Yang, W.Z., 2003 Use of exogenous fibrolytic
enzymes to improve feed utilization by ruminants. Journal of Animal Science 81(E. Suppl. 2), E37–
E47.
9
Beauchemin, K.A., Kreuzer, M., O'Mara, F. & McAllister, T.A., 2008 Nutritional management for enteric
methane abatement: a review. Australian Journal of Experimental Agriculture 48, 21-27. doi:
10.1071/EA07199
Blaxter, K.L. & Clapperton, L., 1965 Prediction of the amount of methane produced by ruminants. The
British Journal of Nutrition 19, 511–522. doi: 10.1079/BJN19650046
Brouwer, E., 1965 Report of subcommittee on constants and factors. Proc. 3rd EAAP Symp. on Energy
metabolism pp. 441-443. Troon, Publ. 11,Academic Press, London
Carulla, J.E., Kreuzer, M., Machmüller, A. & Hess, H.D., 2005 Supplementation of Acacia mearnsii tannins
decreases methanogenesis and urinary nitrogen in forage-fed sheep. Australian Journal of Agricultural
Research 56, 961-970.
Castillo, A.R., Kebreab, E., Beever, D.E. & France, J., 2000 A review of efficiency of nitrogen utilisation in
lactating dairy cows and its relationship with environmental pollution. Journal of Animal & Feed
Sciences 9, 1-32.
Chadwick, D., 1997 Nitrous oxide and ammonia emissions from grassland following applications of slurry:
potential abatement practices. In: Gaseous nitrogen emissions from grasslands. Eds S.C. Jarvis & B.F.
Pain pp. 257–264. CAB International: Wallingford, UK.
Chaucheyras, F., Fonty, G., Bertin, G. & Gouet, P., 1995 In vitro utilization by a ruminal acetogenic
bacterium cultivated alone or in association with an archaea methanogen is stimulated by a probiotic
strain of Saccharomyces cerevisiae. Applied Environmental Microbiology 61, 3466–3467.
Clark, H., Pinares-Patiño, C.S. & de Klein, C.A.M., 2005 Methane and nitrous oxide emissions from grazed
grasslands In: Grassland: A Global Resource. Ed. D.A. McGilloway pp. 279-293. Wageningen
Academic: Wageningen, the Netherlands.
Coffey, M.T., 1996 Environmental challenges as related to animal agriculture – Swine. In: Nutrient
management of food animals to enhance and protect the environment. Ed. E.T. Kornegay pp. 29-39.
CRC: Boca Raton, FL.
Dalal, R., Wang, W., Robertson, G. & Parton, W., 2003 Nitrous oxide emission from Australian agricultural
lands and mitigation options: a review. Australian Journal of Soil Research 41, 165-195.
de Klein, C.A.M. & Eckard, R.J., 2008 Targeted technologies for nitrous oxide abatement from animal
agriculture. Australian Journal of Experimental Agriculture 48, 14-20. doi: 10.1071/EA07217
de Klein, C.A.M. & Ledgard, S.F., 2005 Nitrous oxide emissions from New Zealand agriculture - key
sources and mitigation strategies. Nutrient Cycling in Agroecosystems. 72, 77-85.
de Klein, C.A.M., Sherlock, R.R., Cameron, K.C. & van der Weerden, T.J., 2001 Nitrous oxide emissions
from agricultural soils in New Zealand—a review of current knowledge and directions for future
research. Journal of the Royal Society of New Zealand. 31, 543-574.
de Klein, C.A.M., Smith, L.C. & Monaghan, R.M., 2006 Restricted autumn grazing to reduce nitrous oxide
emissions from dairy pastures in Southland, New Zealand. Agriculture Ecosystems & Environment
112, 192–199. doi: 10.1016/j.agee.2005.08.019
Di, H.J. & Cameron, K.C., 2002 The use of a nitrification inhibitor, dicyandiamide (DCD), to decrease
nitrate leaching and nitrous oxide emissions in a simulated grazed and irrigated grassland. Soil Use
and Management 18, 395-403.
Di, H.J., Cameron, K.C. & Sherlock, R.R., 2007 Comparison of the effectiveness of a nitrification inhibitor,
dicyandiamide, in reducing nitrous oxide emissions in four different soils under different climatic and
management conditions. Soil Use & Management 23, 1-9.
Eckard, R.J., 1989 The response of Italian ryegrass to applied nitrogen in the Natal midlands. Journal of the
Grassland Society of Southern Africa. 61, 19-22.
Eckard, R.J., 1990 The effect of three sources of nitrogen on the dry matter yield, nitrogen and nitrate-N
content of Lolium multiflorum. Journal of the Grassland Society of Southern Africa 73, 208-209.
Eckard, R.J., Bartholomew, P.E.B. & Tainton, N.M., 1995 The yield response of annual ryegrass Lolium
multiflorum to varying nitrogen fertiliser application strategies. South African Journal of Plant & Soil
123, 112-116.
Eckard, R.J., Chapman, D.F. & White, R.E., 2007 Nitrogen balances in temperate perennial grass and clover
dairy pastures in south-eastern Australia. Australian Journal of Agricultural Research 58, 1167-1173.
doi: 10.1071/AR07022
10
Eckard, R.J., Chen, D., White, R.E. & Chapman, D.F., 2003 Gaseous nitrogen loss from temperate grass and
clover dairy pastures in south eastern Australia. Australian Journal of Agricultural Research 54, 561570.
Eckard, R.J., Dalley, D. & Crawford, M., 2000 Impacts of Potential Management Changes on Greenhouse
Gas Emissions and Sequestration from Dairy Production Systems in Australia. Management Options
for Carbon Sequestration in Forest, Agricultural and Rangeland Ecosystems, Workshop Proceedings.
ANU, Canberra. Ed. B.A.L.a.A.H. Keenan R. pp. 58-72. CRC for Greenhouse Accounting. ISBN
0646404318.
Eckard, R.J. & Franks, D.R., 1998 Strategic nitrogen fertiliser use on perennial ryegrass and white clover
pasture in north-western Tasmania. Australian Journal of Experimental Agriculture. 38, 155-160.
Eckard, R.J., Hegarty, R. & Thomas, G., 2002 A decision support framework for greenhouse accounting on
Australian Dairy farms. Dairy Research and Development Corporation, Final Report No. UM10667.
http://www.greenhouse.unimelb.edu.au/site/pdf_files/Final%20ReportUM0667%20Oct%202002.zip
Eckard, R.J., Johnson, I. & Chapman, D.F., 2006a Modelling nitrous oxide abatement strategies in intensive
pasture systems. Proceedings of the 2nd International Conference on Greenhouse Gases and Animal
Agriculture: An Update. Zurich, Switzerland. Ed. T.J. Soliva CR, Kreuser M. pp. 76-85. Dept Animal
Science, ETH Zurich
Eckard, R.J., Johnson I. & Chapman, D.F., 2006b Modelling nitrous oxide abatement strategies in intensive
pasture systems. International Congress Series 1293, 76-85. doi: 10.1016/j.ics.2006.01.027
Forster, P., Ramaswamy, V., Artaxo, P., Berntsen, T., Betts, R., Fahey, D.W., Haywood, J., Lean, J., Lowe,
D.C., Myhre, G., Nganga, J., Prinn, R., Raga, G., Schulz, M. & Van Dorland, R., 2007 Changes in
Atmospheric Constituents and in Radiative Forcing. Cambridge University Press, Cambridge, United
Kingdom and New York, NY, USA.
Fox, R.H., Myers, R.J.K. & Vallis, I., 1990 The nitrogen mineralization rate of legume residues as influenced
by their polyphenol, lignin and nitrogen contents. Plant and Soil 129, 251-259.
Galbally, I., Meyer, C., Bentley, S., Weeks, I., Leuning, R., Kelly, K., Phillips, F., Barker-Reid, F., Gates,
W., Baigent, R., Eckard, R. & Grace, P., 2005 A study of environmental and management drivers of
non-CO2 greenhouse gas emissions in Australian agro-ecosystems. Environmental Sciences 2, 133142. doi: 10.1080/15693430500395396
Grainger, C., Auldist, M.J., Clarke, T., Beauchemin, K.A., McGinn, S.M., Hannah, M.C., Eckard, R.J. &
Lowe, L.B., 2008 Use of Monensin Controlled-Release Capsules to Reduce Methane Emissions and
Improve Milk Production of Dairy Cows Offered Pasture Supplemented with Grain. Journal of Dairy
Science 91, 1159–1165. doi: 10.3168/jds.2007-0319
Grainger, C., Clarke, T., Auldist, M.J., Beauchemin, K.A., McGinn, S.M., Waghorn, G.C. & Eckard, R.J.,
2009 Mitigation of greenhouse gas emissions from dairy cows fed pasture and grain through
supplementation with Acacia mearnsii tannins Canadian Journal of Animal Science (in press).
Granli, T. & Bøckman, O.C., 1994 Nitrous oxide from agriculture. Norwegian Journal of Agricultural
Sciences Supplement 12, 7-128.
Hackstein, J.H.P. & Van Alen, T.A., 1996 Fecal methanogens and vertebrate evolution. Evolution 50, 559572.
Hegarty, R.S., Goopy, J.P., Herd, R.M. & McCorkell, B., 2007 Cattle selected for lower residual feed intake
have reduced daily methane production. Journal of Animal Science 85, 1479-1486. doi:
10.2527/jas.2006-236
Joblin, K.N., 1999 Ruminal acetogens and their potential to lower ruminant methane emissions. Australian
Journal of Agricultural Research 50, 1307-1313.
Johnson, I.R., Chapman, D.F., Snow, V.O., Eckard, R.J., Parsons, A.J., Lambert, M.G. & Cullen, B.R., 2008
DairyMod and EcoMod: Biophysical pastoral simulation models for Australia and New Zealand.
Australian Journal of Experimental Agriculture 48, 621-631. doi: 10.1071/EA07133
Johnson, K.A. & Johnson, D.E., 1995 Methane emissions from cattle. Journal of Animal Science 73, 2483–
2492.
Jordan, C. & Smith, R.V., 1985 Factors affecting leachate of nutrients from an intensively managed
grassland in County Antrim, Northern Ireland. Journal of Environmental Management 20, 1-15.
11
Kelly, K.B., Phillips, F.A. & Baigent, R., 2008 Impact of dicyandiamide application on nitrous oxide
emissions from urine patches in northern Victoria, Australia. Australian Journal of Experimental
Agriculture 48, 156-159. doi: 10.1071/EA07251
Kempton, T.J., Murray, R.M. & Leng, R.A., 1976 Methane production and digestibility measurements in
grey kangaroo and sheep. Australian Journal of Biological Science 29, 209-214.
Ledgard, S.F., 1986 Nitrogen Fertiliser Use on Pastures and Crops. Ministry of Agriculture and Fisheries,
Ruakura, New Zealand.
Ledgard, S.F., Menneer, J.C., Dexter, M.M., Kear, M.J., Lindsey, S., Peters, J.S. & Pacheco, D., 2007a A
novel concept to reduce nitrogen losses from grazed pastures by administering soil nitrogen process
inhibitors to animals: A study with sheep. Agriculture Ecosystems & Environment 124, 148-158. doi:
10.1016/j.agee.2007.12.006
Ledgard, S.F., Welten, B., Menneer, J.C., Betteridge, K., Crush, J.R. & Barton, M.D., 2007b New nitrogen
mitigation technologies for evaluation in the Lake Taupo catchment. Proceedings of the New Zealand
Grasslands Association 69, 117-121.
Luo, J., Ledgard, S.F. & Lindsey, S.B., 2008 A test of a winter farm management option for mitigating
nitrous oxide emissions from a dairy farm. Soil Use and Management 24, 121-130. doi:
10.1111/j.1475-2743.2007.00140.x
McAllister, T.A. & Newbold, C.J., 2008 Redirecting rumen fermentation to reduce methanogenesis.
Australian Journal of Experimental Agriculture 48, 7-13.
McAllister, T.A., Okine, E.K., Mathison, G.W. & Cheng, K.J., 1996 Dietary environmental and
microbiological aspects of methane production in ruminants. Canadian Journal of Animal Science 76,
231–243.
McGinn, S.M., Beauchemin, K.A., Coates, T. & Colombatto, D., 2004 Methane emissions from beef cattle:
effect of monensin, sunflower oil, enzymes, yeast and fumaric acid. Journal of Animal Science 82,
3346–3356.
Min, B.R., Barry, T.N., Attwood, G.T. & McNabb, W.C., 2003 The effect of condensed tannins on the
nutrition and health of ruminants fed fresh temperate forages: a review. Animal Feed Science and
Technology 106, 3–19. doi: 10.1016/S0377-8401(03)00041-5
Misselbrook, T.H., Powell, J.M., Broderick, G.A. & Grabber, J.H., 2005 Dietary manipulation in dairy cattle:
laboratory experiments to assess the influence on ammonia emissions. Journal of Dairy Science 88,
1765–1777.
Moe, P.W. & Tyrrell, H.F., 1979 Methane production in dairy cows. Journal of Dairy Science 62, 1583–
1586.
Mosier, A.R., Parton, W.I. & Hutchinson, G.L., 1983 Modelling nitrous oxide evolution from cropped and
native soils. Environmental Biogeochemistry Ecology Bulletin 35, 229-241.
Newbold, C.J., Wallace, R.J. & McIntosh, F.M., 1996 Mode of action of the yeast Saccharomyces cerevisiae
as a feed additive for ruminants. British Journal of Nutrition 76, 249–261.
Niezen, J.H., Waghorn, G.C., Graham, T., Carter, J.L. & Leathwick, D.M., 2002 The effect of diet fed to
lambs on subsequent development of Trichostrongylus colubriformis larvae in vitro and on pasture.
Veterinary Parasitology 105, 269 283.
Nollet, L., Demeyer, D. & Verstraete, W., 1997 Effect of 2-bromoethanesulfonic acid and
Peptostreptococcus productus ATCC 35244 addition on stimulation of reductive acetogenesis in the
ruminal ecosystem by selective inhibition of methanogenesis. Applied and Environmental
Microbiology 63, 194-200.
Ouwerkerk, D., Klieve, A.V., Forster, R.J., Templeton, J.M. & Maguire, A.J., 2005 Characterization of
culturable anaerobic bacteria from the forestomach of an Eastern Grey Kangaroo, Macropus
giganteus. Letters in Applied Microbiology 41, 327-333.
Palm, C.A. & Sanchez, P.A., 1991 Nitrogen release from the leaves of some tropical legumes as affected by
their lignin and polyphenolic contents. Soil Biology and Biochemistry 23, 83-88.
Phillips, F.A., Leuning, R., Baigent, R., Kelly, K.B. & Denmead, O.T., 2007 Nitrous oxide flux
measurements from an intensively managed irrigated pasture using micrometeorological techniques
Agricultural & Forest Meteorology 143, 92-105.
12
Pinares-Patiño, C.S., Ulyatt, M.J., Lassey, K.R., Barry, T.N. & Holmes, C.W., 2003 Persistence of
differences between sheep in methane emission under generous grazing conditions. The Journal of
Agricultural Science 140, 227-233. doi: 10.1017/S0021859603003071
Russelle, M.P., Browne, B.A., Turyk, N.B. & Pearson, B., 2005 Denitrification under pastures on permeable
soils helps protect ground water quality [abstract]. XXth International Grassland Congress. Dublin,
Ireland. Eds F.P. O'Mara, R.J. Wilkins, L. 't Mannetje, D.K. Lovett, P.A.M. Rogers & T.M. Boland p.
692. Wageningen Academic Publishers
Saggar, S., Andrew, R.M., Tate, K.R., Hedley, C.B., Rodda, N.J. & Townsend, J.A., 2004 Modelling nitrous
oxide emissions from dairy-grazed pastures. Nutrient Cycling in Agroecosystems. 68, 243-255.
Sauer, F.D., Fellner, V., Kinsman, R., Kramer, J.K.G., Jackson, H.A., Lee, A.J. & Chen, S., 1998 Methane
output and lactation response in Holstein cattle with monensin or unsaturated fat added to the diet.
Journal of Animal Science 76, 906-914.
Sayanova, O.V. & Napier, J.A., 2004 Eicosapentanoic acid: biosynthetic routes and the potential for
biosnythesis in transgenic plants. Phytochemistry 65, 147-158. doi: 10.1016/j.phytochem.2003.10.017
Schils, R.L.M., Verhagen, A., Aarts, H.F.M., Kuikman, P.J. & Sebek, L.B.J., 2006 Effect of improved
nitrogen management on greenhouse gas emissions from intensive dairy systems in the Netherlands.
Global Change Biology 12, 382–391. doi: 10.1111/j.1365-2486.2005.01090.x
Smith, L.C., de Klein, C.A.M. & Catto, W.D., 2008 Effect of dicyandiamide applied in a granular form on
nitrous oxide emissions from a grazed dairy pasture in Southland, New Zealand, New Zealand. New
Zealand Journal of Agricultural Research 51, 387–396.
Smith, P., Martino, D., Cai, Z., Gwary, D., Janzen, H., Kumar, P., McCarl, B., Ogle, S., O’Mara, F., Rice, C.,
Scholes, B. & Sirotenko, O., 2007 Agriculture. In: Climate Change 2007: Mitigation. Contribution of
Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate
Change. Eds B. Metz, O.R. Davidson, P.R. Bosch, R. Dave & L.A. Meyer. Cambridge University
Press, Cambridge: United Kingdom and New York, NY, USA.
Somda, Z.C. & Powell, J.M., 1998 Seasonal decomposition of sheep manure and forage leaves in soil.
Communications in Soil Science and Plant Analysis 29, 2961-2979.
Standing Committee on Agriculture, 1990 Feeding standards for Australian livestock: Ruminants. CSIRO,
Australia.
Stevens, R.J. & Laughlin, R.J., 2002 Cattle slurry applied before fertilizer nitrate lowers nitrous oxide and
dinitrogen emissions. Soil Science Society of America Journal 66, 647–652.
Subbarao, G.V., Ishikawa, T., Ito, O., Nakahara, K., Wang, H.Y. & Berry, W.L., 2006 A biolumiuescence
assay to detect nitrification inhibitors released from plant roots: a case study with Brachiaria
humidicola Plant and Soil 288, 101–112. doi: 10.1007/s11104-006-9094-3
Tomkins, N.W. & Hunter, R.A., 2003 Methane mitigation in beef cattle using a patented anti-methanogen.
Proceedings of the 2nd joint Australia and New Zealand forum on non-CO2 greenhouse gas emission
from agriculture, October 2003. Lancemore Hill. Eds R.J. Eckard & W. Slattery p. F3. Australian
Greenhouse Office: Canberra. ISBN 0-9579597-2-9.
Trapnell, L. & Malcolm, B., 2006 Economic Analysis of Changing from a 300 Day Lactation to an Extended
Lactation Dairy System. Proceedings of the Biennial Conference of the Australasian Farm Business
Management Network, September 2006. Marcus Oldham College p. 8p
Ulyatt, M.J., Lassey, K.R., Shelton, I.D. & Walker, C.F., 2002 Methane emission from dairy cows and
wether sheep fed subtropical grass-dominant pastures in midsummer in New Zealand. New Zealand
Journal of Agricultural Research 45, 227–234.
van Groenigen, J.W., Velthof, G.L., Van der Bolt, F.J.E., Vos, A. & Kuikman, P.J., 2005 Seasonal variation
in N2O emissions from urine patches: effects of urine concentration, soil compaction and dung. Plant
and Soil 273, 15–27. doi: 10.1007/s11104-004-6261-2
Van Vugt, S.J., Waghorn, G.C., Clark, D.A. & Woodward, S.L., 2005 Impact of monensin on methane
production and performance of cows fed forage diets. Proceedings of the New Zealand Society of
Animal Production 65, 362-366.
van Vuuren, A.M., van der Koelen, C.J., Valk, H. & de Visser, H., 1993 Effects of partial replacement of
ryegrass by low protein feeds on rumen fermentation and nitrogen loss by dairy cows. Journal of Dairy
Science 76, 2982–2993.
13
Waghorn, G.C., Clark, H., Taufa, V. & Cavanagh, A., 2008 Monensin controlled-release capsules for
methane mitigation in pasture-fed dairy cows. Australian Journal of Experimental Agriculture 48, 6568. doi: 10.1071/EA07299
Waghorn, G.C., Tavendale, M.H. & Woodfield, D.R., 2002 Methanogenesis from forages fed to sheep.
Proceedings of the New Zealand Grassland Association 64, 167–171.
Waghorn, G.C., Woodward, S.L., Tavendale, M. & Clark, D.A., 2006 Inconsistencies in rumen methane
production - effects of forage composition and animal genotype. International Congress Series 1293,
115-118.
Whitehead, D.C., 1995 Grassland nitrogen. CAB International: Wallingford, UK.
Wilson, G.R. & Edwards, M.J., 2008 Native wildlife on rangelands to minimize methane and produce loweremission meat: kangaroos versus livestock. Conservation Letters xx, 1–10. doi: 10.1111/j.1755263X.2008.00023.x
Woodward, S.L., Waghorn, G.C. & Laboyrie, P., 2004 Condensed tannins in birdsfoot trefoil (Lotus
corniculatus) reduced methane emissions from dairy cows. Proceedings of the New Zealand Society of
Animal Production 64, 160–164.
Wright, A.D.G., Auckland, C.H. & Lynn, D.H., 2007 Molecular diversity of methanogens in feedlot cattle
from Ontario and Prince Edward Island, Canada. Applied and Environmental Microbiology 73, 4206–
4210. doi: 10.1128/AEM.00103-07
Wright, A.D.G., Kennedy, P., O’Neill, C.J., Toovey, A.F., Popovski, S., Rea, S.M., Pimm, C.L. & Klein, L.,
2004 Reducing methane emission in sheep by immunization against rumen methanogens. Vaccine 22,
3976-3985. doi: 10.1016/j.vaccine.2004.03.053
14
Technologies to Reduce
Enteric Methane Emissions
Animal
Manipulation
Diet
Manipulation
Rumen
Manipulation
Forage
quality
Animal
Breeding
Residual Feed
Intake
Biological
Control
Plant
Breeding
Bacteriophages
bacteriocins
Efficiency
Reductive
Acetogenesis
Dietary
Supplements
Management
Systems
Dietary Oils
Alternative
livestock systems
Vaccination
Probiotics
Unproductive
Animals
Chemical
Defaunation
Enzymes
Dicarboxylic
acids
Plant Secondary
Compounds
Tannin &
Saponin
Figure 1. A summary of strategies for the abatement of enteric CH4 in ruminants, based on literature
reviewed.
Technologies to reduce
Nitrous Oxide emissions
Animal
Soils
Physical
interventions
Restricted
Grazing
Feed Conversion
Efficiency
Breeding
Plant breeding
eg. tannins
Dietary
Interventions
Chemical
Intgerventions
Balancing
Protein: Energy
Salt
Nitrification
inhibitor in urine
Fertiliser
Rate
Waterlogging /
drainage
Source
Irrigation
Timing
Compaction
Effluent
Management
Controlled
Release
Nitrification
Inhibitors
Figure 2. A summary of strategies for the abatement of N2O from ruminant production systems, based on
literature reviewed.