Enteric methane mitigation technologies for …...Environ Monit Assess (2012) 184:1929–1952 DOI 10.1007/s10661-011-2090-y Enteric methane mitigation technologies for ruminant livestock:

Environ Monit Assess (2012) 184:1929–1952DOI 10.1007/s10661-011-2090-y

Enteric methane mitigation technologies for ruminantlivestock: a synthesis of current researchand future directions

Amlan Kumar Patra

Received: 7 November 2010 / Accepted: 14 April 2011 / Published online: 6 May 2011© Springer Science+Business Media B.V. 2011

Abstract Enteric methane (CH4) emission in ru-minants, which is produced via fermentation offeeds in the rumen and lower digestive tractby methanogenic archaea, represents a loss of2% to 12% of gross energy of feeds and con-tributes to global greenhouse effects. Globally,about 80 million tonnes of CH4 is produced an-nually from enteric fermentation mainly from ru-minants. Therefore, CH4 mitigation strategies inruminants have focused to obtain economic aswell as environmental benefits. Some mitigationoptions such as chemical inhibitors, defaunation,and ionophores inhibit methanogenesis directlyor indirectly in the rumen, but they have notconfirmed consistent effects for practical use. Avariety of nutritional amendments such as increas-ing the amount of grains, inclusion of some legu-minous forages containing condensed tannins andionophore compounds in diets, supplementationof low-quality roughages with protein and readilyfermentable carbohydrates, and addition of fatsshow promise for CH4 mitigation. These nutri-tional amendments also increase the efficiencyof feed utilization and, therefore, are most likely

A. K. Patra (B)Department of Animal Nutrition, West BengalUniversity of Animal and Fishery Sciences, 37, K. B.Sarani, Belgachia, Kolkata, 700037, Indiae-mail: [email protected]

to be adopted by farmers. Several new poten-tial technologies such as use of plant secondarymetabolites, probiotics and propionate enhancers,stimulation of acetogens, immunization, CH4 ox-idation by methylotrophs, and genetic selectionof low CH4-producing animals have emerged todecrease CH4 production, but these require ex-tensive research before they can be recommendedto livestock producers. The use of bacteriocins,bacteriophages, and development of recombinantvaccines targeting archaeal-specific genes and cellsurface proteins may be areas worthy of inves-tigation for CH4 mitigation as well. A combina-tion of different CH4 mitigation strategies shouldbe adopted in farm levels to substantially de-crease methane emission from ruminants. Evi-dently, comprehensive research is needed to ex-plore proven and reliable CH4 mitigation tech-nologies that would be practically feasible andeconomically viable while improving ruminantproduction.

Keywords Methane production · Ruminants ·Mitigation strategies

Introduction

Greenhouse gas (GHG) emissions have becomean increasingly important topic worldwide dueto their effects on global warming and climate

1930 Environ Monit Assess (2012) 184:1929–1952

change. The effects of GHG emissions on theecological and socioeconomic vulnerability havealready been noticed and will continue to growregionally and globally in the years to come (IPCC2007). Carbon dioxide (CO2), methane (CH4),nitrous oxide, hydrofluorocarbons, perflouro-carbons, and sulfur hexafluoride are the impor-tant GHGs that are monitored by the UnitedNations Framework Convention on ClimateChange and have been listed in Annex A ofKyoto Protocol for their mitigation commitment.Global GHG emissions due to human activities(anthropogenic) have grown since the beginningof the industrial revolution with an increase of70% between 1970 and 2004 (IPCC 2007). Carbondioxide is the largest contributor of the anthro-pogenic GHGs representing 76.7% of total an-thropogenic GHG emissions in 2004 (IPCC 2007).The global atmospheric concentration of CO2 hasincreased from a pre-industrial value of about280 to 379 ppm in 2005 (IPCC 2007). Methaneis the second largest anthropogenic GHG, whichcontributes 14.3% of total anthropogenic GHGemissions estimated in 2004 (IPCC 2007). Thepresence of CH4 in the atmosphere was first dis-covered in 1948 from features in the infraredabsorption spectrum (Migeotte 1948) and is nowroutinely monitored in the atmosphere. Theconcentration of CH4 has increased by about1,059 ppbv (i.e. from 715 to 1,774 ppbv in 2005)since 1750 (IPCC 2007). Agricultural emissionsof CH4 account for about 60% of the total CH4

from anthropogenic sources, of which 25% arisesfrom enteric fermentation in livestock (Olivieret al. 2005). Globally, livestock produces about80 million tonnes of enteric CH4 annually. Mostof the CH4 from ruminant livestock originatesfrom microbial fermentation of carbohydrates inthe rumen and lower digestive tract, referred toas enteric CH4 emissions. Methane emissions inruminants also account for a 2% to12% of grossenergy loss of feeds depending upon the type ofdiets (Johnson and Johnson 1995). Therefore, in-hibition of CH4 production in the rumen has beenattempted for more than three decades to increasethe utilization of feed energy for production pur-poses. In recent years, CH4 mitigation researchhas gained momentum because of the greenhouseeffects contributed by CH4.

The global production of meat, milk, and eggshas increased rapidly during the last decade, par-ticularly in countries with rapid economic devel-opment (Steinfeld et al. 2006). The growth oflivestock production is expected to continue overthe next few decades. This will further stimu-late specialization and industrialization of live-stock farming and exacerbate GHG problemsin the absence of adequate mitigation measures(Steinfeld et al. 2006). Hence, there are urgentneeds for development and application of GHGmitigation technologies in livestock productionsystems. Although a number of reports are avail-able on methane abatement technologies (Mosset al. 2000; Beauchemin et al. 2008; McAllisterand Newbold 2008; Eckard et al. 2010), this syn-thesis discusses several CH4 mitigation optionsemphasizing latest developments in this area andidentifies future research needs and challenges inthe mitigation of enteric CH4 emissions.

Microbiology of methanogenesis

In 1776, the great physicist Alessandro Volta ob-served the bubbling of gas in swamps when he wason a boat in his summer holiday. Upon analysisof this gas, he noted that it was flammable andnamed it as “marsh gas.” After nearly a century,it was confirmed that formation of “marsh gas”(now called CH4) in these habitats was a microbialprocess.

In ruminants and pseudo-ruminants like camel-idae, the major portion of the methanogenesisoccurs in the large fermentative chamber knownas rumen, which is located at the beginning of thedigestive tract. The rumen is a complex, diverse,and mostly obligate anaerobic microbial ecosys-tem where feeds including fibrous plant structuresare fermented primarily to short-chain volatilefatty acids, CO2, hydrogen (H2), and CH4 by largenumbers of different genera and species of bacte-ria (1010 to 1012 ml−1), protozoa (105 to 106 ml−1),fungi (104 to 105 ml−1), and methanogens (108

to 1010 ml−1). Methanogens belong to a separatedomain archaea in the kingdom of Euryarchaeotaand are found in a wide range of other anaerobicenvironments (Liu and Whitman 2008). Most ru-men methanogens derive energy for their growth

Environ Monit Assess (2012) 184:1929–1952 1931

through a series of biochemical reduction of CO2

with H2, and some methanogens use acetate andmethyl group-containing compounds to produceCH4 (methanogenesis).

Methanogenesis : 4H2 + CO2 = CH4 + 2H2O

�G◦′ = −135.6 kJ mol−1

Methanogenesis promotes more complete ox-idation of fermented substrates and greater en-ergy recovery by fermenting organisms. Besides,it helps to maintain the low partial pressure ofH2 in the rumen, thus providing a favorable en-vironment for degradation of cell wall carbo-hydrates (Liu and Whitman 2008). Among 28genera and 113 species of methanogens knownto be present in nature, only seven specieshave commonly been cultured from the rumen(Janssen and Kirs 2008). These are Methanobac-terium formicicum, Methanobacterium bryantii,Methanobrevibacter ruminantium, Methanobre-vibacter millerae, Methanobrevibacter olleyae,Methanomicrobium mobile, and Methanoculleusolentangyi. Methanosarcina spp. have also beencultured from the rumen but are not normally amajor part of the archaeal community. Analysis ofmolecular-based studies (Janssen and Kirs 2008)reveals that the members of family Methanobacte-riaceae (which includes Methanobrevibacter spp.,Methanobacterium spp., and Methanosphaeraspp.) are the dominant members (30% to 99%of archaea) of the rumen archaea. Members ofthe order Methanomicrobiales (which includesMethanomicrobium spp.) are less abundant (0%to 54%), and members of the order Methanosarci-nales (which includes Methanimicrococcus) arerare (2% to 3%). Usually, CH4 is producedby two types of methanogens, the slow-growingmethanogens (generation time about 130 h) thatproduces CH4 from acetate (e.g., Methanosarcina)and fast growing methanogens (generation time4–12 h) that reduce CO2 with H2. In the rumen,methanogenesis occurs mostly by the fast-growingmethanogens as ruminal retention times are tooshort to permit establishment of the slow growingspecies (Weimer 1998).

Unlike methanogens, acetogens produce ac-etate by utilizing H2. They act as important H2

sinks in the hindgut fermentation of mammals

and termites. Reductive acetogenesis occurs inthe intestine of non-ruminants, sometimes alongwith methanogenesis and sometimes replacingmethanogenesis (Liu and Whitman 2008).

Acetogenesis : 4H2+2CO2 = CH3COOH+2H2O

�G◦′ = −104.6 kJ mol−1

Acetogens such as Acetomaculum ruminis havebeen isolated from the rumen of most of thedomestic species (e.g. Atwood and McSweeney2008), but population densities of acetogens arehighly variable, ranging from non-detectable to105 ml−1 rumen fluid (LeVan et al. 1998). Ace-togens are the normal flora in the rumen, butmethanogens outcompete acetogens as metha-nogens have lower utilization thresholds for H2

than acetogens and also due to thermodynam-ically more favorable nature of methanogene-sis over acetogenesis (Atwood and McSweeney2008).

Methane mitigation options

A schematic diagram of the potential targets ofdecreasing CH4 emissions from ruminants hasbeen shown in Fig. 1. Some of the CH4 mitigationoptions are confounded with the other possibletargets, but they have been included in a particulartarget considering the main mode of decreasingCH4 production. For example, ionophores candecrease CH4 by manipulating rumen fermenta-tion e.g. by inhibiting hydrogen-producing bacte-ria. They also decrease CH4 production per unitof products as a consequence of improvement ofanimal performances. But ionophore compoundshave been included as a dietary target becausethese compounds are generally used as dietaryfeed additives to increase performance of animals.

Animal inerventions

Number and productivity of animals

Methane production is directly proportional tothe number of animals. Culling of nonproductiveand low-producing animals is often advocated indeveloped countries to curtail the CH4 budget.


Fig. 1 A schematicpresentation of thepotential targets ofdecreasing CH4 emissionsfrom ruminants. Boxes indark shade could be thetargets for suppressingCH4 emissions

Diets

Acetate

Oxaloacetate Malate

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Propionate

CH4

CO2 + H2

Acetate

Methylotrophs

Acetogens Methanogens

Propionate enhancersAmylolytic bacteria

Cellulolytic bacteria

Microbial digestion +Pyruvate H2

CO2 H2++

Animal

Electron acceptors

High concentrates

High roughages

High-producing animals should be maintained inherds. In this way, although total production willbe increased, CH4 emissions per unit of productcould be decreased. This is important so as tosupply growing demand of animal products inthe years ahead while the impact of emissionscould be reduced. However, this is unlikely tobe recommended due to socioeconomic and reli-gious background in many developing countries.Proper livestock management especially in devel-oping countries such as reducing the incidence ofdisease and reproductive problems can decreaseCH4 emission in a herd for each unit of production(Eckard et al. 2010).

Increasing the productivity of animals couldalso lessen CH4 emissions per unit of products.There are many options for enhancing the pro-ductivity of animals such as supplementationof protein and energy to low-quality forages,ionophores, bovine somatotrophin, probiotics,and proper formulation of diets (Moss et al. 2000).In the Third World countries, genetic potentialof animals for production is not expressed due tounder or improper nutrition; thus, CH4 emissioncould be substantially decreased if a proper feed-ing management is practiced. It appears that untila proven and reliable CH4 mitigation technol-ogy is developed, minimizing the number of low-producing and unproductive animals and properfeeding practice with increasing the number of

high-producing animals could limit CH4 emissionwithout affecting the total production of animalproducts.

Genetic selection of animals for decreasingmethane emissions

Recently, it has been studied that CH4 productionfrom different animals under same feeding condi-tions shows significant variation among animals.In trials with grazing sheep, Pinares-Patiño et al.(2003) identified some animals as high and lowCH4 emitters on the basis of CH4 output per unitof feed intake and noted that these differencespersisted all the four measurement periods of5 months when the same type of diet was fed.Although the reason is not clear, it might be dueto variations of methanogen numbers among ani-mals (Zhou et al. 2009). This finding suggests thepossibility of genetic differences between animalsin CH4 production, which could be utilized forgenetic selection for low CH4 production.

Recent research has demonstrated that rumi-nants with low residual feed intake (RFI; i.e.,the difference between actual feed intake and theexpected feed requirements for maintenance andproduction) emit less CH4 than the animals withhigh RFI (Alford et al. 2006; Hegarty et al. 2007).This may offer an opportunity for genetic selec-tion for this trait and it can be selected without


compromising the production traits. For instance,Hegarty et al. (2007) reported that CH4 emissionwas lower in Angus steers selected based on lowRFI than in steers having high RFI (142 vs. 192 gCH4 day−1 or 132 vs. 173 g CH4 kg−1 daily gain)and daily gain was similar in both groups. Thelow CH4 emissions by cattle with low RFI mightbe due to lower methanogen numbers in low RFIcattle than in high RFI cattle (Zhou et al. 2009). Ithas also been suggested that the greater suppres-sion of CH4 could be achieved on low digestibilitydiets, when animals are selected based on low RFI(Hegarty et al. 2007). Thus, this strategy couldbe more advantageous for the tropical countrieswhere low-quality feeds are fed to ruminants.

Dietary intervention

Ionophore compounds

Ionophore antibiotics such as monensin are usu-ally used in ruminants to improve the efficiency ofmeat and milk production. They have also beenshown to depress CH4 production in ruminants indose-dependent manner (Table 1). The CH4 pro-duction has been reported to decrease up to 76%in vitro and to an average of 18% in vivo (VanNevel and Demeyer 1996). Ionophores do notalter the quantity and diversity of methanogens(Hook et al. 2009), but they change the bac-terial population from Gram-positive to Gram-negative organisms with a concomitant changein the fermentation from acetate to propionate.This fermentation shift lowers the availability ofH2 for CH4 production by methanogens. Theymight also reduce ruminal protozoal numbers.Relatively high-dose levels might be required tolessen CH4 compared with doses needed to im-prove feed efficiency. Monensin included in dietsat a dose of <20 mg kg−1 diet may not always haveprofound effect on CH4 production (Beaucheminet al. 2008). Higher doses (24–35 mg kg−1 diet)decreased CH4 production by 4–10% (Van Vugtet al. 2005; Odongo et al. 2007a) with short-termdecreases in CH4 up to 30% at a dose level of33 mg kg−1 diet (Guan et al. 2006). Unfortunately,some long-term trials suggest that the inhibitionof methanogenesis by ionophores may not per-sist over time (Guan et al. 2006). It appears that

monensin can be used for short-term decreases inCH4 emissions, which can also improve efficiencyof feed utilization in ruminants. However, the useof ionophores as feed additives has been bannedin the European Union and is restricted in someother countries as feed additives.

Supplementation

In developing countries, low-quality crop residuesare fed to ruminants, which are deficient in pro-tein, minerals, and vitamins. Dietary supplemen-tation of these low-quality feeds with energy orprotein supplements could reduce CH4 produc-tion as a result of improved efficiency of rumenfermentation. High levels of concentrate feeds indiets increase the propionate production, whichdecreases H2 availability for CH4 production. Forexample, Lovett et al. (2003) reported that in-creasing the ratio of concentrate in the diet ofbeef heifers from 35% to 90% decreased CH4 pro-duction and increased body weight gain. Again,increasing the levels of green fodder such asberseem, oat, and sorghum in straw and stover-based diets may reduce CH4 release. For instance,methane production in crossbred cows decreasedby 33% when green sorghum replaced the wheatstraw by 30% (Haque et al. 2001). Similarly, in-creased feeding of green oat fodder and berseemforage with the wheat straw diets lowered CH4

production by 8% to 23% and 20% to 30%,respectively, depending on the ratios of greenfodders in diets (Singh 2001). The urea-treatedstraw has also shown to lessen CH4 emissionsin sheep (Sahoo et al. 1999). The use of mo-lasses/urea multinutrient blocks has been foundto be a cost-effective diet supplementation strat-egy with potential to reduce CH4 emissions by10% to 25% (Bowman et al. 1992; Srivastavaand Garg 2002) and to increase milk productionat the same time. Benchaar et al. (2001) evalu-ated the effect of a range of dietary strategieson CH4 production using a modeling approachand predicted that CH4 production could be re-duced by increasing concentrate proportions ofdiets (−40%), replacing fibrous concentrates withstarchy concentrates (−22%), with the utilizationof less ruminally degradable starch (−7%), in-creasing the digestibility of forage (−15%), with

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legumes compared to grass forages (−28%), andwith silages compared to hay (−20%).

Forage species

Some legume forages have been shown to de-crease CH4 production in ruminants, which areoften explained by the presence of condensedtannins (CT), low fiber content, high dry matter(DM) intake, and faster rate of passage fromthe rumen (Table 2; Beauchemin et al. 2008).A decrease in CH4 production was observed inRusitec as the proportion of sainfoin (Onobrychisviciifolia) increased in the diets (McMahon et al.1999). Woodward et al. (2002) investigated thefeeding of sulla (Hedysarum coronarium) on CH4

emission and milk yield in Friesian and Jerseydairy cows. Cows fed on sulla produced less CH4

per kg DM intake (19.5 vs. 24.6 g) and per kgmilk solid yield (243.3 vs. 327.8 g). Similar trendsin CH4 emission and milk production have beenobserved in dairy cows fed on birdsfoot trefoil(Lotus corniculatus) silage compared with dairycows fed on ryegrass pasture (Woodward et al.2001). There was also a 16.7% decrease in CH4

production per kg DM intake in lambs fed onlotus (Lotus pedunculatus) compared in lambs fedon lotus and polyethylene glycol (which inacti-vates CT by binding with it), which is attributedto the presence of CT in lotus (Waghorn et al.2002). Animut et al. (2008a) also observed thatfeeding of different levels of kobe lespedeza (Les-pedeza striata) decreased CH4 production linearlyin goats, and it has been attributed to the presenceof CT (Animut et al. 2008b). Furthermore, it hasbeen reported that C3 forages such as ryegrass andwheat might yield less CH4 per unit of digestibleDM than C4 forages such as corn and sorghum(Ulyatt et al. 2002), presumably due to high con-tent of fiber in C4 plants, but more studies areneeded to explain this result.

Suppression of rumen methanogens

Chemical compounds

For a long time, halogenated CH4 analogs andrelated compounds such as chloroform and chlo-ral hydrate were tested for CH4 production in-

hibition in ruminants. However, they cause liverdamage and death of animals after a long periodof feeding. Therefore, it appears that they are notsuitable for use in practice. Amichloral (a hemi-acetal of chloral and starch) decreased CH4 pro-duction and increased live weight gain, but its an-timethanogenic activity decreased gradually withprolonged feeding (Trei et al. 1972). Similarly, theeffects of trichloroacetamide and trichloroethyladipate on ruminal methanogenesis were reportedto be transient. Bromochloromethane and 2-bromoethanesulfonic acid, a bromine analogue ofcoenzyme F involved in methyl group transferduring methanogenesis decreased CH4 outputs(Dong et al. 1999), but their anti-methanogenicactivity was reported to be transient; however,a combination of bromochloromethane and α-cyclodextrin was found to be more stable and werecapable of suppressing CH4 emissions in rumi-nants over a prolonged period (McCrabb et al.1997). Garcia-Lopez et al. (1996) and Kung et al.(2003) reported that 9,10-anthraquinone inhibitedmethanogenesis, and it is speculated that 9,10-anthraquinone inhibits the reduction of methylco-enzyme M to CH4 by uncoupling electrontransfer in methanogens. Recently, iodopropaneboth in vitro (Mohammed et al. 2004a) and insteers without affecting digestibility (Mohammedet al. 2004b), and diallyl maleate in vitro andin vivo (Lila et al. 2004) have been shown tosuppress CH4 production. There was no apparentadaptation of these compounds to ruminal mi-crobes up to 21 (Lila et al. 2004) and 25(Mohammed et al. 2004b) days. Feeding of α-cyclodxtrin iodopropane complex (to preventvolatility and pungent odour of iodopropane) tosteers for a period of 25 days had no appar-ent health problems (Mohammed et al. 2004b).Iodopropane is probably a corrinoid inhibitor thattransfers methyl group to coenzyme M inmethanogens.

Some nitrocompounds such as nitroethane, 2-nitroethanol, 2-nitro-1-propanol, and 3-nitro-1-propionic acid inhibited ruminal CH4 productionin vitro (Anderson et al. 2003, 2008) andnitroethane and 2-nitro-1-propanol have beenshown to reduce CH4-producing activity in vivo(Anderson et al. 2006; Gutierrez-Bañuelos et al.2007). These nitrocompounds probably act by

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al.(

2002

)fo

rage

(6.8

%C

T)

(10

days

)fo

rage

asso

lefe

edun

affe

cted

Les

pede

zacu

neat

aG

oats

L.c

unea

taC

rabg

rass

/tal

l30

.2%

50.2

%T

VF

Aan

dA

/PP

ucha

laet

al.(

2005

)(c

onta

ins

17.7

%C

T)

(120

days

)pa

stur

efe

scue

past

ure

unaf

fect

edL

espe

deza

stri

ata

Goa

tsL

espe

deza

:So

rghu

m-s

udan

32.9

,47.

329

,38.

7D

iges

tibi

lity

and

Ani

mut

etal

.(20

08a)

fora

ge(2

1da

ys)

sorg

hum

-sud

angr

ass

gras

san

d58

.4%

and

74.5

%pr

otoz

oaln

umbe

rs(1

:2,2

:1an

d3:

0)de

crea

sed,

TV

FA

and

A/P

unaf

fect

edL

.str

iata

Goa

tsL

.str

iata

L.s

tria

ta+

49.5

%33

.3%

Dig

esti

bilit

yan

dA

nim

utet

al.(

2008

b)fo

rage

(15.

1%C

T)

(36

days

)as

sole

feed

poly

ethy

lene

prot

ozoa

lnum

bers

glyc

olde

crea

sed,

TV

FA

and

A/P

unaf

fect

edL

otus

pedu

ncul

atus

Shee

pL

.cor

nicu

latu

sR

yegr

ass

past

ure

No

effe

ct28

.9%

c–

Woo

dwar

det

al.(

2001

)fo

rage

(7da

ys)

asso

lefe

edL

.ped

uncu

latu

sSh

eep

L.c

orni

cula

tus

Luc

ern

past

ure

No

effe

ct23

.7%

c–

Woo

dwar

det

al.(

2001

)fo

rage

(7da

ys)

asso

lefe

edL

otus

corn

icul

atus

Dai

ryco

ws

L.c

orni

cula

tus

Rye

gras

ssi

lage

No

effe

ct23

.4%

c–

Woo

dwar

det

al.(

2001

)si

lage

(2.5

9%C

T)

(12

days

)as

sole

feed

(8.5

7%)

L.p

edun

cula

tus

Shee

pL

.ped

uncu

latu

sL

.ped

uncu

latu

s–

5.2%

Dig

esti

bilit

yW

agho

rnet

al.(

2002

)fo

rage

(5.3

%C

T)

(10

days

)fo

rage

asso

lefo

rage

+P

EG

decr

ease

d

TV

FA

tota

lvol

atile

fatt

yac

ids

conc

entr

atio

n,A

/Pac

etat

eto

prop

iona

tera

tio,

CT

cond

ense

dta

nnin

s;P

EG

poly

ethy

lene

glyc

olto

bind

tann

ins

a Inhi

biti

onof

met

hane

prod

ucti

onco

mpa

red

wit

hco

ntro

lon

volu

me

basi

sbIn

hibi

tion

ofm

etha

nepr

oduc

tion

com

pare

dw

ith

cont

rolr

elat

ive

todr

ym

atte

ror

orga

nic

mat

ter

dige

sted

unle

ssot

herw

ise

mar

ked

c Rel

ativ

eto

per

kilo

gram

feed

inta

ke


Tab

le3

Eff

ecto

fadd

itio

nof

fati

ndi

ets

onen

teri

cm

etha

nepr

oduc

tion

invi

vo

Ref

eren

ces

Ani

mal

sD

iet

Dur

atio

nA

dded

Fat

type

Met

hane

prod

ucti

onD

iges

tibi

lity

Milk

yiel

d(R

/C)

(day

s)fa

t%(g

kg−1

DM

inta

ke)a

orA

DG

Con

trol

Fat

a

(Bea

uche

min

etal

.200

7)B

eefh

eife

rs65

:25

213.

4T

allo

w20

.0a

17.8

b=

=Su

nflo

wer

oil

20.0

a17

.7b

==

Sunf

low

erse

eds

20.0

a15

.4–

=(B

eauc

hem

inan

dM

cGin

n20

06)

Bee

fHei

fers

75:2

521

4.6

Can

ola

oil

25.5

21.7

–=

(Bea

uche

min

etal

.200

9)b

Dai

ryco

ws

45:5

528

4.2

Sunf

low

erse

eds

16.3

14.6

–=

3.7

Fla

xse

eds

16.3

a13

.4b

–=

3.9

Can

ola

seed

s16

.3a

13.7

b=

=(H

olte

ret

al.1

992)

Dai

ryco

ws

100:

011

22.

7C

otto

nsee

d13

.4a

12.1

b–

–(J

orda

net

al.2

006a

)B

eefh

eife

r50

:50

351.

33C

ocon

utoi

l28

.325

.9=

NR

2.71

Coc

onut

oil

28.3

a24

.1b

=N

R4.

57C

ocon

utoi

l28

.3a

21.1

b–

NR

(Jor

dan

etal

.200

6b)

Bee

fhei

fer

50:5

074

8.0

Coc

onut

oil

27.5

a22

.1b

=+

7.4

Cop

ram

eal

27.5

a23

.6b

–=

(Jor

dan

etal

.200

6c)

Bee

fhei

fer

10:9

010

36.

0So

ybea

noi

l12

.7a

8.0b

NR

+So

ybea

nse

eds

12.7

a10

.8b

NR

=(L

ovet

teta

l.20

03)

Bee

fhei

fer

65:3

5to

10:9

077

4.65

Coc

onut

oil

22.4

a17

.3b

NR

=(M

achm

ülle

ret

al.2

003a

)bSh

eep

57:4

315

6.0

Coc

onut

oil

18.3

17.5

NR

NR

(Mac

hmül

ler

etal

.200

3b)

Shee

p1:

1.5

and

1:0.

515

5.0

Myr

isti

cac

id23

.4a

13.7

b=

NR

(Mac

hmül

ler

and

Kre

uzer

1999

)Sh

eep

71:2

923

3.5

Coc

onut

oil

24.8

a19

.4b

=N

R45

:54

237.

0C

ocon

utoi

l24

.8a

8.8b

=N

R(M

aoet

al.2

010)

Lam

b60

:40

603.

0So

ybea

noi

l18

.6a

16.0

bN

R=

(Mar

tin

etal

.200

8)D

airy

cow

s65

:35

284.

2C

rude

linse

ed21

.1a

18.9

b–

=4.

4E

xtru

ded

linse

ed21

.1a

15.5

b–

–5.

8L

inse

edoi

l21

.1a

10.1

b–

–(M

cGin

net

al.2

004)

Bee

fcat

tle

75:2

521

5.7

Sunf

low

eroi

l22

.6a

18.8

b=

NR

(Odo

ngo

etal

.200

7b)

Dai

ryco

ws

61:3

911

5.0

Myr

isti

cac

id28

.4a

19.5

bN

R=

Met

hane

prod

ucti

onda

tafo

llow

edby

smal

llet

ters

inro

wdi

ffer

atP

<0.

05.R

/Cfo

rage

toco

ncen

trat

era

tio,

AD

Gav

erag

eda

ilybo

dyw

eigh

tgai

n,N

Rno

trep

orte

da W

hen

met

hane

valu

esw

ere

notp

rese

nted

asgr

ams

per

kilo

gram

DM

inta

ke,t

heva

lues

wer

eca

lcul

ated

from

the

repo

rted

data

bC

ontr

oldi

etw

asad

ded

wit

hru

men

prot

ecte

dfa

t


inhibiting H2 and formate oxidation (Andersonet al. 2008). Although these studies on chemicalantimethanogenic agents show promise to lowerCH4 emissions, research on these chemical feedadditives is unlikely to be continued due to publicconcerns over chemical residues in products ofanimal origins. If these compounds are supportedfor use as antimethanogenic compounds due tonoble cause of reducing greenhouse effects, thereis need of thorough research for their effects onanimal health and presence of these chemicals inanimal products along with the withdrawal periodof these compounds.

Fat addition

Fat inclusion in the diets causes a decrease inCH4 production depending upon the levels of fatsupplementation, fat sources, forms of fat sup-plementation, and types of diet (Table 3). Irre-spective of fat sources, CH4 emissions (grams perkilogram of DM intake) were calculated to bereduced by 5.6% with each 1% addition of fats(Beauchemin et al. 2008). A decrease in CH4 pro-duction by fat supplementation may be mediatedthrough combined influences on the inhibition ofgrowth of methanogens and protozoal numbersand reduction of ruminal organic matter (OM)fermentation and hydrogenation of unsaturatedfatty acids (acting as a alternative H2 sink) in therumen. There are considerable variations in theCH4 reduction among fat sources, with marked re-duction occurring for refined medium chain fattyacids (i.e., C12:0 and C14:0) such as coconut oil(64% at 7% level), myristic oil (58% at 5% level),canola oil, and palm kernel oil compared withC18 fatty acids (Machmüller and Kreuzer 1999;Machmuller et al. 2003a, b). Although fat inclu-sion in diets lowers CH4 emissions consistentlyfor long periods, fat particularly at concentrationsabove 6–7% of dietary DM can significantly di-minish DM digestion particularly fiber compo-nents and DM intake, and again the severity ofthe effect varies with the fat used and type ofdiets (Machmüller et al. 2003b; Beauchemin et al.2008). Besides, high levels of added fat can reducemilk fat percentage and daily gain or milk yield(Martin et al. 2008). Therefore, care must be takenin choosing the appropriate fat sources and level

of fat supplementation. Fat supplementation in-creases the energy density of diets, which mightalso improve animal performance (Grainger et al.2008) and feed efficiency despite reduced feedintake (Jordan et al. 2006b, c). Sometimes, fat sup-plementation decreases or does not affect the per-formances of animals; however, it suppresses CH4

outputs per unit of products. For example, feed-ing of whole soybean seeds did not affect bodyweight gain but lowered CH4 emissions per kilo-gram gain (Jordan et al. 2006c). Similarly, fat sup-plementation through extruded linseed decreasedmilk yield probably due to reduced feed intakeand digestibility, but significantly decreased CH4

emissions per kilogram of milk yield. In contrast,supplementation of fat through whole cottonseeddecreased CH4 (grams per day or gram of perunit of products) and also increased milk pro-duction when dairy cows grazed in low qualitypastures (Grainger et al. 2008). It appears thatproper supplementation of fat is a promising tech-nology for mitigation of CH4 on consistent basiswithout affecting production. However, cost offat supplementation with edible oils might not beeconomical for the livestock producers.

Plant secondary compounds

Recently, bioactive plant metabolites have beenan important area of research to substitute chem-ical feed additives. Many phytochemicals such assaponins, tannins, essential oils (Table 4), andmany other unknown metabolites from a widerange of plant sources show potential for CH4

mitigation options (Kamra et al. 2008; Patra et al.2008; Patra and Saxena 2010). These metaboliteslessen CH4 production through a direct effect onmethanogens and/or elimination of protozoa, re-duction of OM digestion, and modification of fer-mentation in the rumen (Patra and Saxena 2010).

Saponins There is increasing evidence to suggestthat addition of saponins in the diets might dimin-ish CH4 production, which is likely due to a de-crease in protozoal numbers and/or methanogenicarchaeal activity. Saponins of Sapindus saponariasuppressed CH4 production by 20% withoutaffecting methanogen numbers in Rusitec (Hesset al. 2003) or in lamb (Hess et al. 2004). Agarwal


Tab

le4

Eff

ects

ofph

ytoc

hem

ical

son

invi

vom

etha

nepr

oduc

tion

and

ferm

enta

tion

inth

eru

men

Phy

toch

emic

als

Ani

mal

sD

osag

eD

iet

Met

hane

Met

hane

Com

men

tsR

efer

ence

s(d

urat

ion)

(R/C

)in

hibi

tion

ain

hibi

tion

b

Sapo

nins

Luc

erne

sapo

nins

Shee

p0.

2to

0.8

gkg

−110

0:0

No

effe

ctN

oef

fect

Dig

esti

bilit

yde

crea

sed

at2

Klit

aet

al.(

1996

)(2

7.8%

sapo

nins

)(1

4da

ys)

BW

0.75

or10

toan

d4%

conc

entr

atio

ns;

40g

kg−1

diet

TV

FA

and

A/P

unaf

fect

ed;

Qui

llaja

sapo

nari

aex

trac

tSh

eep

13.5

gkg

−1di

etor

60:4

016

.9%

21.7

%T

VF

Ade

crea

sed,

Pen

etal

.(20

07)

(5to

7%sa

poni

ns)

(18

days

)16

.1g

day−

1(n

oef

fect

)di

gest

ibili

ty,A

/Pan

dun

affe

cted

Q.s

apon

aria

plan

tC

attl

e10

gkg

−1of

DM

51:4

9N

oef

fect

7%D

iges

tibi

lity,

TV

FA

and

Hol

tsha

usen

etal

.(20

09)

(3%

sapo

nins

)(2

8da

ys)

A/P

unaf

fect

edSa

pind

ussa

pona

ria

frui

tsSh

eep

5g

kg−1

BW

0.75

49.2

to6.

5%7.

8%D

iges

tibi

lity

and

A/P

Hes

set

al.(

2004

)(2

1da

ys)

56:2

1de

crea

sed;

TV

FA

and

met

hano

gens

num

bers

incr

ease

dSa

poni

nsSh

eep

170

mg

day−

1or

75:2

515

.5%

13.7

%D

iges

tibi

lity

unaf

fect

ed,

Wan

get

al.(

2009

)(1

5da

ys)

0.13

gkg

−1di

etA

/Pde

crea

sed,

TV

FA

incr

ease

dSa

rsap

onin

Shee

p0.

12g

kg−1

diet

70:3

07.

1%6.

7%D

iges

tibi

lity,

TV

FA

and

Sant

oso

etal

.(20

04)

(15

days

)A

/Pun

affe

cted

Sars

apon

inSh

eep

0.00

2an

d0.

03g

kg−1

50:5

0N

oef

fect

1.4

and

Dig

esti

bilit

y,T

VF

A,A

/PSl

iwin

skie

tal.

(200

2)(1

.25%

sapo

nins

)(2

1da

ys)

DM

ofsa

rsap

onin

−2.2

%un

affe

cted

,T

easa

poni

nsL

amb

3g

day−

1or

60:4

027

.2%

28.3

%c

TV

FA

incr

ease

d;A

/PM

aoet

al.(

2010

)(6

0da

ys)

4.1

gkg

−1di

etun

affe

cted

;met

hano

gen

num

bers

decr

ease

dT

easa

poni

nsSh

eep

5g

day−

1or

60:4

08.

71%

–T

VF

Aan

dA

/Pun

affe

cted

Yua

net

al.(

2007

)(2

1da

ys)

5g

kg−1

diet

Yuc

casc

hidi

gera

extr

act

Shee

p13

.8g

kg−1

diet

or60

:40

11.7

%15

.6%

TV

FA

decr

ease

d,P

enet

al.(

2007

)(8

to10

%sa

poni

ns)

(18

days

)16

.4g

day−

1(n

oef

fect

)di

gest

ibili

tyan

dA

/Pun

affe

cted

Y.s

chid

iger

apl

ant

Dai

ryco

ws

10g

kg−1

ofD

M51

:49

No

effe

ct2.

5%D

iges

tibi

lity,

TV

FA

and

Hol

tsha

usen

etal

.(20

09)

(6%

sapo

nins

)(2

8da

ys)

A/P

unaf

fect

ed


Tab

le4

(con

tinu

ed)

Phy

toch

emic

als

Ani

mal

sD

osag

eD

iet

Met

hane

Met

hane

Com

men

tsR

efer

ence

s(d

urat

ion)

(R/C

)in

hibi

tion

ain

hibi

tion

b

Tan

nins

Aca

cia

mea

rnsi

iSh

eep

41g

kg−1

diet

50:5

09.

9%7.

0%D

iges

tibi

lity

and

Car

ulla

etal

.(20

05)

extr

act(

CT

72.5

%)

(21

days

)T

VF

Aun

affe

cted

,A

/Pde

crea

sed

A.m

ears

iita

nnin

sC

attl

e8.

6an

d14

.6g

kg−1

Gra

zed

on17

.0an

d30

%13

.9an

dD

iges

tibi

lity

decr

ease

dG

rain

ger

etal

.(20

09)

(14

days

)of

DM

inta

kepa

stur

ew

ith

22.4

%d

4.5

kggr

ain/

day

A.m

ears

iita

nnin

sC

attl

e8.

6an

d14

.6g

kg−1

Gra

zed

on11

.5an

d28

%8.

1an

dD

iges

tibi

lity

decr

ease

dG

rain

ger

etal

.(20

09)

(35

days

)of

DM

inta

kepa

stur

ew

ith

20.2

%d

4.5

kggr

ain

day−

1

Cas

tane

asa

tiva

Shee

p5

and

10.1

gkg

−150

:50

−21.

5−1

7.9

and

Dig

esti

bilit

y,T

VF

A,

Sliw

insk

ieta

l.(2

002)

woo

dex

trac

t(2

1da

ys)

DM

equi

vale

nt(a

t10.

1g

kg−1

)−2

1.7%

A/P

unaf

fect

ed(c

onta

ins

HT

20%

)to

1an

d2

gkg

−1to

32.6

%pu

reta

nnin

s(a

t5g

kg−1

)T

erm

inal

iach

ebul

aSh

eep

10g

kg−1

50:5

0N

oef

fect

24.0

%D

iges

tibi

lity

incr

ease

dP

atra

etal

.(20

10b)

seed

pulp

(35

days

)D

Min

take

Ess

enti

aloi

lsC

inna

mal

dehy

deSh

eep

0.02

gkg

−1di

etB

arle

y-ba

sed

diet

––

No

effe

cton

Ohe

ne-A

djei

etal

.(20

08)

(91

days

)m

etha

noge

nic

coun

ts,i

ncre

ased

dive

rsit

yof

met

hano

gens

Juni

per

berr

yoi

lSh

eep

0.02

gkg

−1di

etB

arle

y-ba

sed

diet

––

No

effe

cton

met

hano

gen

Ohe

ne-A

djei

etal

.(20

08)

[Jun

iper

usco

mm

unis

](9

1da

ys)

num

bers

,inc

reas

edth

edi

vers

ity

ofm

etha

noge

ns

R/C

roug

hage

toco

ncen

trat

era

tio,

TV

FA

tota

lvo

lati

lefa

tty

acid

sco

ncen

trat

ion,

DM

dry

mat

ter,

A/P

acet

ate

topr

opio

nate

rati

o,C

Tco

nden

sed

tann

ins,

HT

hydr

olys

able

tann

ins

a Inhi

biti

onof

met

hane

prod

ucti

onco

mpa

red

wit

hco

ntro

l(w

itho

utph

ytoc

hem

ical

s)on

volu

me

basi

sbIn

hibi

tion

ofm

etha

nepr

oduc

tion

com

pare

dw

ith

cont

rol(

wit

hout

phyt

oche

mic

als)

rela

tive

todr

ym

atte

r/or

gani

cm

atte

rdi

gest

edun

less

othe

rw

ise

mar

ked

cR

elat

ive

tope

rki

logr

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et al. (2006) reported that the depression inCH4 production was 96%, 39.4%, and 20%with ethanol, water, and methanol extracts ofseed pulps of Sapindus murkossi, respectively,compared with controls. However, saponins ex-tracted from pods of Acacia concinna extractsdid not affect CH4 production in 1:1 concentrateto roughage-based diet despite a depression inprotozoal numbers (Patra et al. 2006a). It hasbeen observed that effect of S. saponaria on CH4

was more pronounced in defaunated (29%) thanfaunated (14%) rumen fluid indicating that re-duced CH4 production was not entirely due toassociated depression in protozoal numbers (Hesset al. 2003). The inhibitory activities of somesaponins on methanogenesis are dependent onthe composition of diets and levels of saponinsin the diets. For example, saponins of Sapin-dus rarak fruits reduced methanogen RNA con-centration at the highest saponins concentration(4 mg ml−1), while lower levels had no effect onmethanogens numbers (Wina et al. 2005). Goelet al. (2008) noted that CH4 inhibition effect ofsaponins from Sesbania sesban and fenugreek waspronounced in concentrate-based diets comparedwith roughage-based diets. Total archaeal popu-lation was reduced by saponins extracted fromS. sesban leaves (78%), fenugreek seeds (22%),and Knautia leaves (21%). Despite inhibition ofarchaea, CH4 production was not affected in theirstudy (Goel et al. 2008), which might be due tochanges in the rate of methanogenesis as a resultof changing fermentation pattern and microbialdiversity.

One of the problems of using saponins orsaponin-containing plants is that anti-protozoalactivity was found to be transient (Patra andSaxena 2009). Protozoa did not become resis-tant to these anti-protozoal compounds (Newboldet al. 1997). Therefore, it is possible that bacterialpopulations of the rumen degraded the saponinsor saponin-containing plants (Newbold et al. 1997;Patra and Saxena 2009). These studies are pro-viding evidence that rumen-mixed microbial pop-ulations are able to adapt to saponins over time,which present a challenge for practical applica-tion of this feed additive technology. Nonethe-less, in addition to suppressing methane outputs,the use of saponins may also confer nutritional

benefits as they might increase microbial proteinsynthesis due to inhibition of protozoa, and thefiber-degrading bacteria and fungi in the rumenmight increase, which is beneficial for utilizationof feeds in low-quality-based diets (Patra andSaxena 2009).

Tannins Different sources of tannin extractshave been shown to decrease CH4 productionboth in vitro and in vivo condition dependingupon doses. Addition of Acacia mearnsii tanninextracts suppressed CH4 production in sheep by10% (Carulla et al. 2005) and in cattle up to30% (Grainger et al. 2009) decreased methano-genesis. Methane production was also inhibitedby inclusion of methanol extract of pericarp ofTerminalia chebula (a tropical fruit) in vitro upto 90% (Patra et al. 2006a) and in sheep fed10 g kg−1 of DM intake (Patra et al. 2010b),which could be due to the presence of tanninsespecially hydrolysable tannins in these fruits. Minet al. (2005) found that quebracho tannin (75%CT) included at concentrations of 1 to 2 g L−1

decreased CH4 production by 12.3% to 32.6% inan in vitro condition. Similarly, feeding of que-bracho tannins at 10–20 g kg−1 DM intake tocattle grazing wheat grass in reproductive stagewith rumen liquor collected from them for testingCH4 production in vitro caused a decrease in CH4

production by 25% to 51% (Min et al. 2006).But cattle grazing wheat grass in vegetative stagedid not exhibit anti-methanogenic effect in thisstudy (Min et al. 2006). More recently, Bhattaet al. (2009) reported that quebracho tannins in-hibited the CH4 production linearly (13% to 45%)with increasing doses (5% to 25% of substrates).However, Beauchemin et al. (2007) did not findany effect on methanogenesis when a quebrachotannin extract (10–20 g kg−1 DM intake) was fedto beef cattle, which may be due to low dosagesof tannins. It has been suggested that the action ofCT on methanogenesis may be attributed to thedirect inhibitory effects on methanogens depend-ing upon the chemical structure of CT and alsoindirectly by decreasing fiber degradation (Patraand Saxena 2010).

Essential oils and organosulfur compoundsA number of reports are available showing


abatement of CH4 production by essential oils(EO) and organosulfur compounds. Evans andMartin (2000) observed that thymol (400 mg L−1),a main component of EO derived from Thymusand Origanum plants, was a strong inhibitorof CH4 in vitro, but acetate and propionateconcentrations also decreased. Methanol andethanol extracts of Foeniculum vulgare andSyzygium aromaticum inhibited CH4 productionin vitro (Patra et al. 2006b, 2010a), which wasalso accompanied by reduction of degradabilityof feeds by S. aromaticum, whereas the extractsof A. sativum and F. vulgare had no effects ondegradability of feeds (Patra et al. 2010a). Withorganosulfur compounds, i.e., garlic oil and fourof its main components (diallyl sulfide, diallyldisulfide, allyl mercaptan, and allicin), Busquetet al. (2005) observed that garlic oil and diallyldisulfide (300 mg L−1 of ruminal fluid) reducedCH4 production by 74% and 69%, respectively,without altering digestibility of nutrients in batchcultures. Busquet et al. (2005) suggested thatgarlic oil and diallyl disulfide might have inhibitedCH4 production due to the direct inhibition ofrumen methanogenic archaea. In an experimentwith sheep fed on wheat straw and concentrate(1:1), inclusion of Allium sativum at 10 g kg−1

of DM intake also reduced CH4 production perunit of OM digested and increased digestibility offiber (Patra et al. 2010b).

A limited number of studies are availableshowing direct effect of EO on rumen archaea.In a culture-based study, EO did not inhibitMethanobrevibacter smithii up to a concentra-tion of 0.16 ml L−1 although inhibition occurredat 1.0 ml L−1 (McIntosh et al. 2003). Ohene-Adjei et al. (2008) also reported that cinnamalde-hyde, garlic, and juniper oil supplementation inbarley-based diet did not affect total numberof methanogenic archea quantified by arecheal16S rRNA. Interestingly, the phylogenetic analy-sis indicated that cinnamaldehyde, garlic, and ju-niper oil supplementation reduced the proportionof clones associated within the M. ruminantium-related cluster, which was more pronounced forjuniper berry oil supplementation. Conversely,clones affiliated to Methanosphaera stadtmanaeand M. smithii and some uncultured groups in-

creased in the supplemented treatments. This sug-gested that EO increased the phylogenetic dis-tribution of methanogenic archaea, which mayhave resulted from changes in associated proto-zoal species (Ohene-Adjei et al. 2008). Agarwalet al. (2009) reported that inclusion of 0.33 ml/Lof peppermint oil increased methanogen numbersby two-fold although there was a decrease in CH4

production by 20% without affecting volatile fattyacid production. In this study, the higher levels(1 and 2 ml L−1) of peppermint oil decreasedtotal methanogen population and CH4 produc-tion. It appears that a decrease in methanogen-esis at low doses might be associated with thechanges in the rate of methanogenesis by archaeadue to the alteration of archaeal community orin the activity of CH4-producing genes (Ohene-Adjei et al. 2008). Overall, although phytochem-icals look promising in suppressing CH4 emis-sions in ruminants, results are not consistent indifferent studies because of great variations inchemical composition of phytochemicals, doses,and feed composition (Patra and Saxena 2010). Agreat deal of research would be needed based onstructure–activity relationship for practical appli-cation of phytochemicals.

Defaunation

Removal of protozoa (defaunation) from the ru-men is often associated with an increased micro-bial protein supply and improvement of animalproductivity (Patra and Saxena 2009). Besides,many methanogens remain attached on the ex-terior surface of rumen ciliate protozoa and asendosymbionts within the ciliates, which are re-sponsible for up to 37% of rumen methanogenesis(Finlay et al. 1994). Hence, defaunation has beensuggested as a way to reduce CH4 productionwith little or minimal effect on rumen digestion.Morgavi et al. (2008) showed that CH4 emissiondecreased by 20% for a period of 2 years indefaunated sheep. However, partial defaunationis not always found to be effective in decreasingCH4 production; the reason of which is unclear(Patra et al. 2006a; Hegarty et al. 2008). A va-riety of techniques for defaunation have beentested experimentally, but none is used routinely


because of toxicity problems to the rest of therumen microbial population and the host animals(Moss et al. 2000). In recent years, there has beenan increased interest for use of plant secondarymetabolites as potential defaunating agents. Inparticular, saponin-containing plants look promis-ing as a possible mean of suppressing or elimi-nating protozoa in the rumen without inhibitingbacterial activity (Agarwal et al. 2006; Patra andSaxena 2009). Recently, it has been reported thatvaccination of sheep with entodinial or mixed pro-tozoal antigens reduced protozoal numbers, andIgG antibodies generated against rumen protozoaremained active and continued to bind target cellsfor up to 8 h (Williams et al. 2008). Defaunationtechnology needs further assessment for practicaldelivery at farmers’ fields.

Immunization against methanogens

In order to inhibit methanogens without affectinguseful ruminal microbes, it is essential to havemethanogen-specific targets for inhibitors. Aus-tralian researchers demonstrated for the firsttime that the vaccination against methanogensmay be another plausible method for mitigatingCH4 emission (Wright et al. 2004). Immuniza-tion of sheep with a mixed whole-cell prepa-ration from three methanogens reduced CH4

production by 7.7% (grams per kilogram of DMintake). However, immunization with a mixedwhole-cell preparation from seven methanogensdid not affect CH4 production in sheep (Wrightet al. 2004). Canadian researchers prepared IgYantibodies in chicken eggs against methanogensgenerated by inoculating hens with whole-cellpreparations of three species of methanogens(Cook et al. 2008). When egg powder containinganti-methanogen antibodies was added in in vitrobatch cultures, CH4 production reduced at 12 hof incubation but not at 24 h of incubation. Thisresult suggests that antibodies may only have atransient influence on methanogens, possibly dueto degradation of antibodies or diversification ofmethanogen population (McAllister and Newbold2008). Because the diversity of methanogens maybe influenced by diets and geographic location, itis a challenge to prepare broad spectrum vaccines

that will be effective across different productionsystems of geographically diverse regions.

Archaeal-specific genes and cell surface pro-teins in M. ruminantium and other methanogenscould be an area of research to discover poten-tial targets for CH4 mitigation and methanogenvaccine development (Atwood and McSweeney2008). More recently, Leahy et al. (2010) iden-tified several gene targets to inhibit CH4 in M.ruminantium via chemogenomic and vaccine ap-proaches and showed that vaccinations of sheepwith synthetic peptides against some gene tar-gets raised antibody titers in serum. Vaccina-tion of sheep with subcellular fractions such ascytoplasmic and cell wall preparations, and cellwall-derived proteins or whole cells of M. rumi-nantium augmented antibody in the sera againstmethanogens, and antibodies inhibited the growthof M. ruminantium and CH4 production in vitro(Wedlock et al. 2010). Development of a recom-binant vaccine against methanogens’ cell surfaceproteins that are conserved across a broad rangeof methanogen species may be successful as a CH4

mitigation technique in future.

Use of bacteriocins

Bacteriocins are bacterial proteins or peptidesproduced by bacteria and play a role in compe-tition among microbial species for niches withinthe ruminal ecosystem. Bovicin HC5, a bacteri-ocin produced by Streptococcus species from therumen, was reported to suppress CH4 productionin vitro by 50% (Lee et al. 2002). Nisin, a bacteri-ocin from Lactobacillus lactis subsp. lactis, has alsobeen shown to decrease CH4 production in vitro.Combinations of nisin and nitrate, an alternativeelectron acceptor, have been reported to lessenCH4 emissions in sheep (Sar et al. 2005). The useof bacteriocins may be prospective for inhibitingmethanogen populations in the rumen.

Bacteriophage therapy

Bacteriophages are microbial viruses that infectboth bacteria and methanogens and lyse theirhost cells during the lytic phase of their develop-ment. Rumen bacteriophages are present in high


numbers (>109 ml−1) in rumen fluid. Possibly un-til now, no phages specific to rumen methanogenshave been isolated from rumen fluid (McAllisterand Newbold 2008). However, phages with activ-ity against other rumen bacteria and non-rumenmethanogens have been reported. Identificationof rumen phages against methanogens that pos-sess activity specifically against methanogensmight be an area of exploration.

Alternate hydrogen sinks

Propionate enhancers

A decrease in CH4 production up to 20–50% bysuppression of methanogens could be achievablewithout reducing feed intake and body weightgain and could increase energetic efficiency to 2–5% of digestion (Atwood and McSweeney 2008).However, utilization of H2 through alternative av-enues should be considered to ameliorate thedepression of fiber digestion in the rumen whenmethanogens are inhibited. Use of propionate en-hancers and other electron acceptors and stim-ulation of reductive acetogenesis appear to bepromising for disposal of H2 Addition of organicacids that are intermediates of propionate forma-tion such as malate and fumarate increases propi-onate production with a stoichiometric decreasein H2 availability for CH4 production. Kolveret al. (2004) noted a 38% lower in CH4 produc-tion when fumarate was added at a dose level of3.5 g L−1 in continuous fermenters with foragesas a substrate. Acrylate, an alternative precursorof propionate, also depresses CH4 production inrumen, but to a lesser extent than an equimolaraddition of fumarate. Similarly, increasing con-centrations of malate (0%, 3.75%, and 7.5% ofDM intake) in the diet of beef cattle lowereddaily CH4 emissions linearly with a decrease of16% at the highest dosage, which correspondedto a 9% reduction per unit of DM intake (Foleyet al. 2009). However, the results are not con-sistent depending upon the dose levels and di-ets (Foley et al. 2009). For example, CH4 emis-sions were not affected by addition of fumarate(10 g kg−1) in the diet of beef cattle (Beaucheminand McGinn 2006), while CH4 outputs from sheepwere decreased by feeding of higher level of fu-

marate (10% of diet) to the extent of 40% to75% per kg of DM intake, and there was an im-provement of animal performance (Wallace et al.2006). The inconsistency of these acids on CH4

production might be due to the conversion ofthese acids to acetate instead of propionate thatstoichiometrically may increase CH4 productionin the rumen (Ungerfeld et al. 2007). In addition,methanogenic microorganisms can predominateover fumarate reducing bacteria at low hydrogenconcentrations normally present in the rumen be-cause the affinity of fumarate-utilizing bacteria toH2 may be lower than the affinity of methanogens(Asanuma et al. 1999). Therefore, it is neces-sary to identify physiological and biochemicalconditions, which could favor propionate ratherthan acetate production from these organic acids(Atwood and McSweeney 2008).

Besides inconsistent results, propionate en-hancers generally are required at high doses tolessen CH4, which makes this an expensive tech-nology. These organic acids are found in leavesof forages, and malate can account for about 6–7% of DM of lucerne forage in immature stage,which declines rapidly with the maturity of plantsresulting malate concentrations of 3% to 4.5% atday 42 (Callaway et al. 1997; Martin 1998). It hasbeen suggested that selection of forages for highmalate content and the plant breeding programsto enhance the concentrations of this organic acidin forages may be economically reasonable forinclusion of malate in the diets (Martin 1998) and,hence, for the CH4 mitigation technology.

Alternative electron acceptors

The methanogenesis could also be suppressed byincreasing the utilization of H2 by organisms otherthan methanogens. Some rumen microorganismscapable of reduction of nitrate to nitrite andthen nitrite to ammonia use hydrogen or formateor both as the common electron donors; thus,methanogenesis may be lowered by the additionof electron acceptors such as nitrate and sulfate(Sar et al. 2004a, b).

NO−3 + 2H+ → H2O + NO−

2

NO−2 + 6H+H2O + NH3

3HCO−2 + NO−

2 + 5H+CO2 + NH−4 + 2H2O


The end product of sulfate metabolism, i.e.,hydrogen sulfide could be toxic, but nitrate couldbe preferably utilized as an electron acceptor sincethe end product of nitrate metabolism by rumenmicrobes is ammonia. It has been generally sug-gested that CH4 production could be diminishedby 10% for each 1% inclusion of potassium ni-trate in a diet (Leng 2008). Another advantage ofusing nitrate is that it could be used as a nitro-gen supplement to low-quality crop residue-baseddiets. In a study of Sar et al. (2004b), feeding ofsodium nitrate (1.3 g kg−1 BW0.75) for 7 days tosheep suppressed CH4 production by 50% and theammonia concentration in the rumen increased.However, under some nutritional conditions/feedmanagement, nitrate becomes toxic because of theaccumulation of nitrite in the rumen. It has beensuggested that the application of nitrate coulddecrease enteric CH4 production by 50%, andtoxicity problems could be reduced by changingthe production management to low protein dietsand a gradual introduction of nitrate to animals(Leng 2008).

Stimulation of acetogens

An alternative strategy to reduce ruminal metha-nogenesis could be to redirect H2 from metha-nogens to acetogens by reductive acetogenesispathway.

Lopez et al. (1999) found that acetogens de-pressed CH4 production when added to rumenfluid in vitro. Research indicated that some se-lected acetogens can lower H2 concentration whenmethanogenesis is inhibited in vitro (LeVan et al.1998). Therefore, acetogens might also be promis-ing alternative sink for H2 in the rumen once CH4

mitigation strategies are applied. It is suggestedthat a decrease in H2 concentration in the rumenusing the acetogens as a daily fed feed additive,even a stable population of acetogens could notbe established in the rumen (Lopez et al. 1999).

Inclusion of probiotic cultures

Probiotics are used in the diets of ruminant toimprove health status, rumen fermentation, andanimal performance, which could also cut downCH4 emissions as discussed earlier. While there

are many studies on rumen fermentation and ani-mal performance, limited information is availableon the effect of probiotic cultures such as Saccha-romyces cerevisiae and Aspergillus oryzae on CH4

production and most of all are in vitro. Addition ofS. cerevisiae to an in vitro system suppressed CH4

formation by 10% initially, though this was notsustained (Mutsvangwa et al. 1992). Lynch andMartin (2002) reported a 20% decrease in CH4

after 48 h of incubation of mixed rumen microor-ganisms in the presence of alfalfa and a live yeastproduct. A. oryzae has been found to lower CH4

production to the extent of 50% (Frumholtz et al.1989), which was directly related to a reductionin the protozoal population (45%). In some ex-periments, A. oryzae and S. cerevisiae increasedCH4 production (Martin et al. 1989; Martin andNisbet 1990), while Mathieu et al. (1996) reportedthat S. cerevisiae addition did not affect CH4 re-lease in vivo. Mwenya et al. (2004) reported thata yeast culture containing Trichosporon sericeum(4 g day−1) depressed CH4 production by 10%in sheep fed on a roughage-based diet. It is sug-gested that yeast culture probably stimulates theacetogens to compete with methanogens or toco-metabolize H2 thus decreasing CH4 formation(Chaucheyras et al. 1995; Mwenya et al. 2004).These conflicting results on CH4 production mightbe due to strain differences between yeast cul-tures and type of diets (Newbold and Rode 2006).Thus, selection of probiotic strains for the CH4-suppressing effect could be attempted. This sug-gests that more research is required before it canbe recommended that yeast cultures can decreaseCH4 production in ruminants.

Rumen methane oxidation

Microbial oxidation of CH4 to CO2 and H2

by CH4 oxidizing bacteria (methanotrophs) inthe rumen has been proposed to reduce entericCH4 production. Methanotrophs (Proteobacteria)have been isolated from a wide range of environ-ments, including the rumen, but there has been lit-tle investigation on physiology and molecular evi-dence of their role in methanotrophy in the rumen(Mitsumori et al. 2002). Some in vitro studies withrumen fluid suggest that oxidation of CH4 to CO2

is of little quantitative significance (0.2–0.5% of


total CH4 produced) in the rumen (Kajikawa et al.2003). The importance of these methanotrophs inthe rumen warrants further investigation in termsof their novelty and practical implication in reduc-ing CH4 emissions from ruminants (Atwood andMcSweeney 2008).

Conclusions

A large number of the potential options discussedabove have only been tested experimentally, andthus need more research to confirm their prospec-tive contributions to curb CH4 emissions in fieldconditions. Farmers are unlikely to adopt abate-ment technologies unless there are positive im-pacts on cost-effective animal production. Theabatement strategies that improve feed efficiencyor productivity such as using high-quality forages,supplementation with concentrates and green fod-ders, use of monensin and fats, incorporation ofCT-containing forages, and maintenance of high-producing animals in the herds are more likely tobe encouraging to the farmers with the presenttechnologies. In this way, CH4 emissions per unitof product can be reduced, and total animal pro-duction can be increased. Accounting the costof technology and the price of the product gain,Sirohi et al. (2007) analyzed that supplementa-tion of diets with monensin (rumensin), concen-trates, and urea molasses mineral block could becost-effective for high-yielding animals in Indiansituation.

A number of the technologies such as use ofplant secondary metabolites, probiotics, and or-ganic acids, stimulation of acetogens, and immu-nization against methanogens have emerged tolower CH4 production. However, most of thesehave not been tried in long-term experiments indifferent nutritional feeding management systemsand thus require extensive research. The CH4

oxidation by methylotrophs, use of bacteriocinsand bacteriophases, and development of recom-binant vaccines targeting archaea-specific genesand cell surface proteins might be an area worthyof investigation for CH4 mitigation. Evidently,comprehensive research is needed to develop CH4

mitigation technologies that will provide consis-tent results. Simultaneously, a broad understand-

ing of both the rumen microbial ecology andmethanogen biochemistry are required for suc-cessful achievement of CH4 mitigation.

There are concerns that inhibiting the CH4

production in the rumen may increase the CH4

emission from manure. For example, reductionsin enteric CH4 emission in cow fed lauric acid waslargely compensated by increases in CH4 emissionfrom manure (Kulling et al. 2002). Similarly, de-creases in enteric CH4 per kilogram of dry matterintake (−18%) were diminished to −12% of totalCH4 via the opposite trend in slurry methanogen-esis (Hindrichsen et al. 2006). In contrast, CH4

inhibition in the rumen may also decrease CH4

production from manure during composting. Sup-plementation with A. mearsii CT in the diet ofcattle decreased CH4 production by 23% duringmanure composting (Hao et al. 2010). This couldbe a concern for generation of CH4 as biogasusing manure from these animals in biodigesters.However, it is argued that lowering enteric CH4

emission could be considered profitable since thisCH4 is inevitably lost whereas manure storagetechnology or anaerobic digester processes couldoffer opportunities to avoid high CH4 losses orproduce CH4 as biogas (Kulling et al. 2002).Nevertheless, an integrated and holistic approachshould be taken into deliberation for CH4 miti-gation depending upon the manure managementsystems.

Acknowledgements The research grant provided byIndian Council of Agricultural Research, New Delhi isgratefully acknowledged.

References

Agarwal, N., Kamra, D. N., Chaudhary, L. C., & Patra,A. K. (2006). Effect of Sapindus mukorossi extractson in vitro methanogenesis and fermentation charac-teristics in buffalo rumen liquor. Journal of AppliedAnimal Research, 30, 1–4.

Agarwal, N., Shekhar, C., Kumar, R., Chaudhary, L. C., &Kamra, D. N. (2009). Effect of peppermint (Menthapiperita) oil on in vitro methanogenesis and fermenta-tion of feed with buffalo rumen liquor. Animal FeedScience and Technology, 148, 321–327.

Alford, A. R., Hegarty, R. S., Parnell, P. F., Cacho, O. J.,Herd, R. M., & Griffith, G. R. (2006). The impactof breeding to reduce residual feed intake on entericmethane emission from the Australian beef industry.


Australian Journal of Experimental Agriculture, 46,813–820.

Anderson, R. C., Callaway, T. R., Van Kessel, J. S., Jung,Y. S., Edrington, T. S., & Nisbet, D. J. (2003). Effectof select nitrocompounds on ruminal fermentation; aninitial look at their potential to reduce economic andenvironmental costs associated with ruminal methano-genesis. Bioresource Technology, 90, 59–63.

Anderson, R. C., Carstens, G. E., Miller, R. K., Callaway,T. R., Schultz, C. L., Edrington, T. S., et al. (2006).Effect of oral nitroethane and 2-nitropropanol admin-istration on methane-producing activity and volatilefatty acid production in the ovine rumen. BioresourceTechnology, 97, 2421–2426.

Anderson, R. C., Krueger, N. A., Stanton, T. B., Callaway,T. R., Edrington, T. S., Harvey, R. B., et al. (2008).Effects of select nitrocompounds on in vitro rumi-nal fermention during conditions of limiting or excessadded reductant. Bioresource Technology, 99, 8655–8661.

Animut, G., Goetsch, A. L., Puchala, P., Patra, A. K.,Sahlu, T., Varel, V. H. et al. (2008a). Methane emis-sion by goats consuming diets with different levelsof condensed tannins from lespedeza. Animal FeedScience and Technology, 144, 212–227.

Animut, G., Goetsch, A. L., Puchala, P., Patra, A. K.,Sahlu, T., Varel, V. H. et al. (2008b). Methane emis-sion by goats consuming different sources of con-densed tannins. Animal Feed Science and Technology,144, 228–241.

Asanuma, N., Iwamoto, M., & Hino, T. (1999). Effectof the addition of fumarate on methane productionby ruminal microorganisms in vitro. Journal of DairyScience, 82, 780–787.

Atwood, G., & McSweeney, C. S. (2008). Methanogengenomics to discover targets for methane mitigationtechnologies and options for alternative H2 utiliza-tion in the rumen. Australian Journal of ExperimentalAgriculture, 48, 28–37.

Beauchemin, K. A., & McGinn, S. M. (2006). Methaneemissions from beef cattle: Effects of fumaric acid,essential oil and canola oil. Journal of Animal Science,84, 1489–1496.

Beauchemin, K. A., McGinn, S. M., & Petit, H. V. (2007).Methane abatement strategies for cattle: Lipid sup-plementation of diets. Canadian Journal of AnimalScience, 87, 431–440.

Beauchemin, K. A., Kreuzer, M., O’Mara, F., &McAllister, T. A. (2008). Nutritional managementfor enteric methane abatement: A review. AustralianJournal of Experimental Agriculture, 48, 21–27.

Beauchemin, K. A., McGinn, S. M., Benchaar, C., &Holtshausen, L. (2009). Crushed sunflower, flax, orcanola seeds in lactating dairy cow diets: Effectson methane production, rumen fermentation, andmilk production. Journal of Dairy Science, 92, 2118–2127.

Benchaar, C., Pomar, C., & Chiquette, J. (2001). Evalua-tion of diet strategies to reduce methane production inruminants: A modelling approach. Canadian Journalof Animal Science, 81, 563–574.

Bhatta, R., Uyeno, Y., Tajima, K., Takenaka, A.,Yabumoto, Y., Nonaka, I., et al. (2009). Difference inthe nature of tannins on in vitro ruminal methane andvolatile fatty acid production and on methanogenicarchaea and protozoal populations. Journal of DairyScience, 92, 5512–5522.

Bowman, R. L., Croucher, J. C., & Picard, M. T.(1992). Assessment of the Pre-feasibility of StrategicSupplementation as an Opportunity for ReducingMethane Emissions in Gujarat, India. Washington,D.C.: Global Change Division, U.S. EnvironmentalProtection Agency.

Busquet, M., Calsamiglia, S., Ferret, A., Carro, M. D., &Kamel, C. (2005). Effect of garlic oil and four of itscompounds on rumen microbial fermentation. Journalof Dairy Science, 88, 4393–4404.

Callaway, T. R., Martin, S. A., Wampler, J. L., Hill, N. S., &Hill, G. M. (1997). Malate content of forage varietiescommonly fed to cattle. Journal of Dairy Science, 80,1651–1655.

Carulla, J. E., Kreuzer, M., Machmuller, A., & Hess,H. D. (2005). Supplementation of Acacia mearnsii tan-nins decreases methanogenesis and urinary nitrogenin forage-fed sheep. Australian Journal of AgriculturalResearch, 56, 961–970.

Chaucheyras, F. G., Fonty, G., Bertin, G., & Gouet, P.(1995). In vitro H2 utilization by a ruminal acetogenicbacterium cultivated alone or in association with anarchaea methanogen is stimulated by a probiotic strainof Saccharomyces cerevisiae. Applied and Environ-mental Microbiology, 61, 3466–3467.

Cook, S. R., Maiti, P. K., Chaves, A. V., Benchaar, C.,Beauchemin, K. A., & McAllister, T. A. (2008). Avian(IgY) anti-methanogen antibodies for reducing rumi-nal methane production: In vitro assessment for theireffects. Australian Journal of Experimental Agricul-ture, 48, 260–264.

Dong, Y., Bae, H. D., MaAllister, T. A., Mathison, G. W.,& Cheng, K. J. (1999). Effects of exogenous fibrolyticenzymes, 2-bromoethanesulfonate, and monensin onfermentation in rumen simulation (RUSITEC) sys-tem. Canadian Journal of Animal Science, 79, 491–498.

Eckard, R. J., Grainger, C., & de Klein, C. A. M. (2010).Options for the abatement of methane and nitrousoxide from ruminant production: A review. LivestockScience, 130, 47–56.

Evans, J. D., & Martin, S. A. (2000). Effects of thymol onruminal micro-organisms. Current Microbiology, 41,336–340.

Finlay, B. J., Esteban, G., Clarke, K. J., Williams, A. G.,Embley, T. M., & Hirt, R. R. (1994). Some ru-men ciliates have endosymbiotic methanogens. FEMSMicrobiology Letters, 117, 157–162.

Foley, P. A., Kenny, D. A., Callan, J. J., Boland, T. M.,& O’Mara, F. P. (2009). Effect of DL-malic acid sup-plementation on feed intake, methane emission, andrumen fermentation in beef cattle. Journal of AnimalScience, 87, 1048–1057.

Frumholtz P. P., Newbold C. J., & Wallace R. J. (1989).Influence of Aspergillus oryzae fermentation extracton the fermentation of a basal ration in the rumen


simulation technique (Rusitec). Journal of Agricul-tural Science (Cambridge), 113, 169–172.

Garcia-Lopez, P. M., Kung, L. Jr., & Odom, J. M. I. (1996).In vitro inhibition of microbial methane productionby 9,10- anthraquinone. Journal of Animal Science, 74,2276–2284.

Goel, G., Makkar, H. P. S., & Becker, K. (2008).Effect of Sesbania sesban and Carduus pycnocephalusleaves and fenugreek (Trigonella foenum-graecum L.)seeds and their extracts on partitioning of nutri-ent from roughage and concentrate based feeds tomethane. Animal Feed Science and Technology, 147,72–89.

Grainger, C., Clarke, T., Beauchemin, K. A., McGinn,S. M., & Eckard, R. J. (2008). Supplementation withwhole cottonseed reduces methane emissions and in-creases milk production of dairy cows offered a forageand cereal grain diet. Australian Journal of Experi-mental Agriculture, 48, 73–76.

Grainger, C., Clarke, T., Auldist, M. J., Beauchemin, K. A.,McGinn, S. M., Waghorn, G. C. et al. (2009). Potentialuse of Acacia mearnsii condensed tannins to reducemethane emissions and nitrogen excretion from graz-ing dairy cows. Canadian Journal of Animal Science,89, 241–251.

Guan, H., Wittenberg, K. M., Ominski, K. H., & Krause,D. O. (2006). Efficacy of ionophores in cattle dietsfor mitigation of enteric methane. Journal of AnimalScience, 84, 1896–1906.

Gutierrez-Bañuelos, H., Anderson, R. C., Carstens, G. E.,Slay, L. J., Ramlachan, N., Horrocks, S. M. et al.(2007). Zoonotic bacterial populations, gut fermenta-tion characteristics and methane production in feedlotsteers during oral nitroethane treatment and after thefeeding of an experimental chlorate product. Anaer-obe, 13, 21–31.

Hao, X., Benke, M. B., Li, C., Larney, F. J., Beauchemin,K. A., & McAllister, T. A. (2010). Greenhouse gasemissions during composting of manure from cattlediets including corn dried distillers grains with solublesand condensed tannins. In Proceedings of abstracts,Greenhouse Gases and Animal Conference, October3–8, 2010, Canada, p.30.

Haque, N., Saraswat, M. L., & Sahoo, A. (2001). Methaneproduction and energy balance in crossbred malecalves fed on rations containing different ratios ofgreen sorghum and wheat straw. Indian Journal ofAnimal Sciences, 71, 797–799.

Hegarty, R. S., Goopy, J. P., Herd, R. M., & McCorkell, B.(2007). Cattle selected for lower residual feed intakehave reduced daily methane production. Journal ofAnimal Science, 85, 1479–1486.

Hegarty, R. S., Bird, S. H., Vanselow, B. A., & Woodgate,R. (2008). Effects of the absence of protozoa frombirth or from weaning on the growth and methaneproduction of lambs. British Journal of Nutrition, 100,1220–1227.

Hess, H. D., Monsalve, L. M., Lascano, C. E., Carulla, J. E.,Diaz, T. E., & Kreuzer, M. (2003). Supplementation ofa tropical grass diet with forage legumes and Sapindussaponaria fruits: Effects on in vitro ruminal nitrogen

turnover and methanogenesis. Australian Journal ofAgricultural Research, 54, 703–713.

Hess, H. D., Beuret, R. A., Lotscher, M., Hindrichsen, I. K.,Machmüller, A., Carulla, J.E. et al. (2004). Ruminalfermentation, methanogenesis and nitrogen utilizationof sheep receiving tropical grass hay-concentrate dietsoffered with Sapindus saponaria fruits and Cratyliaargentea foliage. Animal Science, 79, 177–189.

Hindrichsen, I. K., Wettstein, H. -R., Machmuller, A.,& Kreuzer, M. (2006). Methane emission, nutrientdegradation and nitrogen turnover in dairy cows andtheir slurry at different milk production scenarios withand without concentrate supplementation. Agricul-ture, Ecosystems and Environment, 113, 150–161.

Holter, J. E., Hayes, H. H., & Urban, W. E. Jr. (1992).Energy balance and lactation response in Holsteincows supplemented with cottonseed with or withoutcalcium soap. Journal of Dairy Science, 75, 1480–3494.

Holtshausen, L., Chaves, A. V., Beauchemin, K. A.,McGinn, S. M., McAllister, T. A., Odongo, N. E.,Cheeke, P. R., &Benchaar, C. (2009). Feedingsaponin-containing Yucca schidigera and Quillajasaponaria to decrease enteric methane production indairy cows. Journal Dairy Science, 92, 2809–2821.

Hook, S. E., Northwood, K. S., Wright, A. -D. G., &McBride, B. W. (2009). Long-term monensin supple-mentation does not significantly affect the quantity ordiversity of methanogens in the rumen of the lactatingdairy cow. Applied and Environmental Microbiology,75, 374–380.

IPCC (2007). Summary for Policymakers. In Solomon,S. D., Qin, M., Manning, Z., Chen, M., Marquis, K. B,Averyt, M. T., & Miller, H. L. (Eds.), Climate change2007: The physical science basis. Contribution of work-ing group i to the fourth assessment report of the in-tergovernmental panel on climate change. CambridgeUniversity Press, Cambridge.

Janssen, P. J., & Kirs, M. (2008). Structure of the archaealcommunity of the rumen. Applied and EnvironmentalMicrobiology, 74, 3619–3625.

Johnson, K. A., & Johnson, D. E. (1995). Methane emis-sions from cattle. Journal of Animal Science, 73, 2483–2492.

Jordan, E., Lovett, D. K., Hawkins, M., Callan, J. J., &O’Mara, F. P. (2006a). The effect of varying levels ofcoconut oil on intake, digestibility and methane outputfrom continental cross beef heifers. Animal Science,82, 859–865.

Jordan, E., Lovett, D. K., Monahan, F. J., Callan, J., Flynn,B., & O’Mara, F. P. (2006b). Effect of refined coconutoil or copra meal on methane output and on intakeand performance of beef heifers. Journal of AnimalScience, 84, 162–170.

Jordan, E., Kenny, D., Hawkins, M., Malone, R., Lovett,D. K., & O’Mara, F. P. (2006c). Effect of refinedsoy oil or whole soybeans on intake, methane output,and performance of young bulls. Journal of AnimalScience, 84, 2418–2425.

Joyner, A. E. Jr., Brown, L. J., Fogg, T. J., & Rossi, R. T.(1979). Effect of monensin on growth, feed efficiency


and energy metabolism of lambs. Journal of AnimalScience, 48, 1065–1069.

Kajikawa, H., Valdes, C., Hillman, K., Wallace, R. J., &Newbold, C. J. (2003). Methane oxidation and its cou-pled electron-sink reactions in ruminal fluid. Letters inApplied Microbiology, 36, 354–357.

Kamra, D. N., Patra, A. K., Chatterjee, P. N., Kumar, R.,Agarwal, N., & Chaudhary, L. C. (2008). Effect ofplant extract on methanogenesis and microbial profileof the rumen of buffalo: A brief overview. AustralianJournal of Experimental Agriculture, 48, 175–178.

Klita, P. T., Mathison, G. W., Fenton, T. W., & Hardin,R. T. (1996). Effects of alfalfa root saponins on diges-tive function in sheep. Journal of Animal Science, 74,1144–1156.

Kolver, E. S., Aspin, P. W., Jarvis, G. N., Elborough, K. M.,& Roche, J. R. (2004). Fumarate reduces methaneproduction from pasture fermented in continuousculture. Proceedings of the New Zealand Society ofAnimal Production, 64, 155–159.

Kulling, D. R., Dohme, F., Menzi, H., Sutter, F.,Lischer, P., & Kreuzer, M. (2002). Methane emis-sions of differently fed dairy cows and correspondingmethane and nitrogen emissions from their manureduring storage. Environmental Monitoring and Assess-ment, 79, 129–150.

Kung, L. Jr., Smith, K. A., Smagala, A. M., Endres, K. M.,Bessett, C. A., Ranjit, N. K. et al. (2003). Effectsof 9,10-anthraquinone on ruminal fermentation, total-tract digestion, and blood metabolite concentrations insheep. Journal of Animal Science, 81, 323–328.

Leahy, S. C., Kelly, W. J., Altermann, E., Ronimus,R. S., Yeoman, C. J., Pacheco, D. M. et al. (2010).The genome sequence of the rumen methanogenMethanobrevibacter ruminantium reveals new possi-bilities for controlling ruminant methane emissions.PLoS One, 5, e8926. doi:10.1371/journal.pone.0008926

Lee, S. S., Hsu, J. T., Mantovani, H. C., & Russell, J. B.(2002). The effect of bovicin HC5, a bacteriocin fromStreptococcus bovis BC5, on ruminal methane produc-tion in vitro. FEMS Microbiology Letters, 217, 51–55.

Leng, R. A. (2008). The potential of feeding nitrateto reduce enteric methane production in ruminants.A Report to the Department of Climate Change,Commonwealth Government of Australia CanberraACT Australia, pp. 90.

LeVan T. D., Robinson, J. A., Ralph, J., Greening, R. C.,Smolenski, W. J., Leedle, J. A. Z. et al. (1998). As-sessment of reductive acetogenesis with indigenousruminal bacterium populations and Acetomaculum ru-minis. Applied and Environmental Microbiology, 64,3429–2436.

Lila, Z. A., Mohammed, N., Tatsuoka (Ajisaka), N.,Kanda, S., Kurokawa, Y., & Itabashi, H. (2004). Effectof cyclodextrin diallyl maleate on methane produc-tion, ruminal fermentation and microbes in vitro andin vivo. Animal Science Journal, 75, 15–22.

Liu, Y., & Whitman, W. B. (2008). Metabolic, phyloge-netic, and ecological diversity of the methanogenic ar-chaea. Annals of NewYork Academy of Sciences, 1125,171–189.

Lopez, S. M., McIntosh, F. M., Wallace, R. J., &Newbold, C. J. (1999). Effect of adding acetogenicbacteria on methane production by mixed rumenmicro-organisms. Animal Feed Science and Technol-ogy, 78, 1–9.

Lovett, D. K., Lovell, S., Stack, L., Callan, J., Finlay, M.,Conolly, J. et al. (2003). Effect of forage/concentrateratio and dietary coconut oil level on methane outputand performance of finishing beef heifers. LivestockProduction Science, 84, 135–146.

Lynch, H. A., & Martin, S. A. (2002). Effects of Saccha-romyces cerevisiae culture and Saccharomyces cere-visiae live cells on in vitro mixed ruminal microorgan-ism fermentation. Journal of Dairy Science, 85, 2603–2608.

Machmüller, A., & Kreuzer, M. (1999). Methane suppres-sion by coconut oil and associated effects on nutri-ent and energy balance in sheep. Canadian Journal ofAnimal Science, 79, 65–72.

Machmüller, A., Soliva, C. R., & Kreuzer, M. (2003a).Effect of coconut oil and defaunation treatment onmethanogenesis in sheep. Reproduction Nutrition andDevelopment, 43, 41–55.

Machmüller, A., Soliva, C. R., & Kreuzer, M. (2003b).Methane suppressing effect of myristic acid in sheepas affected by dietary calcium and forage proportion.British Journal of Nutrition, 90, 529–540.

Mao, H. -L., Wang, J. -K., Zhou, Y. -Y., & Liu, J. -X.(2010). Effects of addition of tea saponins and soy-bean oil on methane production, fermentation andmicrobial population in the rumen of growing lambs.Livestock Science, 129, 56–62.

Martin, S. A. (1998). Manipulation of ruminal fermenta-tion with organic acids: A review. Journal of AnimalScience, 76, 3123–3132.

Martin, S. A., & Nisbet, D. J. (1990). Effects of As-pergillus oryzae fermentation extract on fermentationof amino acids, bermudagrass and starch by mixedruminal micro-organisms in vitro. Journal of AnimalScience, 68, 2142–2149.

Martin S. A., Nisbet, D. J., & Dean, R. G. (1989). Influenceof a commercial yeast supplement on the in vitro ru-minal fermentation. Nutrition Reproduction Interna-tional, 40, 395–403.

Martin, C., Rouel, J., Jouany, J. P., Doreau, V., & Chilliard,Y. (2008). Methane output and diet digestibility in re-sponse to feeding dairy cows crude linseed, extrudedlinseed, or linseed oil. Journal of Animal Science, 86,2642–2650.

Mathieu, F., Jouany, J. P., Senaud, J., Bohatier, J., Berthin,G., & Mercier, M. (1996). The effect of Saccharomycescerevisiae and Aspergillus oryzae on fermentations inthe rumen of faunated and defaunated sheep; proto-zoal and probiotic interactions. Reproduction Nutri-tion Development, 36, 271–287.

McAllister, T. A., & Newbold, C. J. (2008). Redirect-ing rumen fermentation to reduce methanogenesis.Australian Journal of Experimental Agriculture, 48,7–13.

McCrabb, G. J., Berger, K. T., Magner, T., May, C., &Hunter R. A. (1997). Inhibiting methane production

http://dx.doi.org/10.1371/journal.pone.0008926


in Brahman cattle by dietary supplementation with anovel compound and the effects on growth. AustralianJournal of Agricultural Research, 48, 323–329.

McGinn, S. M., Beauchemin, K. A., Coates, T., &Colombatto, D. (2004). Methane emissions from beefcattle: Effects of monensin, sunflower oil, enzymes,yeast, and fumaric acid. Journal of Animal Science, 82,3346–3356.

McIntosh, F. M., Williams, P., Losa, R., Wallace, R. J.,Beever, D. A., & Newbold, C. J. (2003). Effectsof essential oils on ruminal microorganisms andtheir protein metabolism. Applied and EnvironmentalMicrobiology, 69, 5011–5014.

McMahon, L. R., Majak, W., McAllister, T. A., Hall, J. W.,Jones, G. A., Popp, J. D. et al. (1999). Effect of sain-foin on in vitro digestion of fresh alfalfa and bloat insteers. Canadian Journal of Animal Science, 79, 203–212.

Migeotte, M. V. (1948). Methane in earth’s atmosphere.Journal of Astrophysics, 107, 400–403.

Min, B. R., Pinchak, W. E., Fulford, J. D., & Puchala,R. (2005). Wheat pasture bloat dynamics, in vitro ru-minal gas production, and potential bloat mitigationwith condensed tannins. Journal of Animal Science, 83,1322–1331.

Min, B. R., Pinchak, W. E., Anderson, R. C., Fulford, J. D.,& Puchala, R. (2006). Effects of condensed tanninssupplementation level on weight gain and in vitro andin vivo bloat precursors in steers grazing winter wheat.Journal of Anima Science, 84, 2546–2554.

Mitsumori, M., Ajisaka, N., Tajima, K., Kajikawa, H.,& Kurihara, M. (2002). Detection of Proteobacteriafrom the rumen by PCR using methanotroph-specificprimers. Letters in Applied Microbiology, 35, 251–255.

Mohammed, N., Lila, Z. A., Ajisaka, N., Hara, K., Mikuni,K., Hara, K. et al. (2004a). Inhibition of ruminalmicrobial methane production by beta-cyclodextriniodopropane, malate and their combination in vitro.Journal of Animal Physiology and Animal Nutrition,88, 188–195.

Mohammed, N., Lila, Z. A., Tatsuoka (Ajisaka), N.,Hara, K., Mikuni, K., Hara, K. et al. (2004b). Effectsof cyclodextrin-iodopropane complex on methaneproduction, ruminal fermentation and microbes, di-gestibility and blood metabolites in steers. AnimalScience Journal, 75, 131–137.

Morgavi, D. P., Jouany, J. -P., & Martin, C. (2008). Changesin methane emission and rumen fermentation para-meters induced by refaunation in sheep. AustralianJournal of Experimental Agriculture, 48, 69–72.

Moss, A. R., Jouany, J. -P., & Newbold, C. J. (2000).Methane production by ruminants: its contribution toglobal warming. Annales de Zootechnie, 49, 231–253.

Mutsvangwa, T., Edward, I. E., Topps, J. H., & Paterson,G. F. M. (1992). The effect of dietary inclusion of yeastculture (Yea-Sacc) on patterns of rumen fermenta-tion, food intake and growth of intensively fed bulls.Animal Production, 55, 35–40.

Mwenya, B., Santoso, B., Sar, C., Gamo, Y., Kobayashi, T.,Arai, I. et al. (2004). Effects of including 1,4-galacto-oligosaccharides, lactic acid bacteria or yeast culture

on methanogenesis as well as energy and nitrogenmetabolism in sheep. Animal Feed Science and Tech-nology, 115, 313–326.

Newbold, C. J., & Rode, L. M. (2006). Dietary additives tocontrol methanogenesis in the rumen. In Soliva, C. R.,Takahashi, J., and Kreuzer, M. (Eds.), GreenhouseGases and Animal Agriculture: An Update (pp. 138–147). Amsterdam: Elsevier. International CongressSeries No. 1293.

Newbold, C. J., Hassan, S. M. E., Wang, J., Ortega, M. E.,& Wallace, R. J. (1997). Influence of foliage fromAfrican multipurpose tree on activity of rumen proto-zoa and bacteria. British Journal of Nutrition, 78, 237–249.

Odongo, N. E., Bagg, R., Vessie, G., Dick, P., Or-Rashid,M. M., Hook, S. E. et al. (2007a). Long-term effects offeeding monensin on methane production in lactatingdairy cows. Journal of Dairy Science, 90, 1781–1788.

Odongo, N. E., Or-Rashid, M. M., Kebreab, E., France, J.,& McBride, B. W. (2007b). Effect of supplementingmyristic acid in dairy cow rations on ruminal methano-genesis and fatty acid profile in milk. Journal of DairyScience, 90, 1851–1858.

Ohene-Adjei, S., Chaves, A. V., McAllister, T. A.,Benchaar, C., Teather, R. M., & Forster, R. J. (2008).Evidence of increased diversity of methanogenic ar-chaea with plant extract supplementation. MicrobialEcology, 56, 234–242.

Olivier, J. G. J., van Aardenne, J. A., Dentener, F.,Ganzeveld, L., & Peters, J. A. H. W. (2005). Re-cent trends in global greenhouse gas emissions: Re-gional trends and spatial distribution of key sources.In A. van Amstel (Ed.) Non-CO2 greenhouse gases(NCGG-4) (pp. 325–330). Rotterdam: Millipress.

Patra, A. K., & Saxena, J. (2009). The effect and modeof action of saponins on microbial populations andfermentation in the rumen and ruminant production.Nutrition Research Reviews, 22, 204–219.

Patra, A. K., & Saxena, J. (2010). A new perspective on theuse of plant secondary metabolites to inhibit methano-genesis in the rumen. Phytochemistry, 71, 1198–1222.

Patra, A. K., Kamra, D. N., & Agarwal, N. (2006a). Effectof plant extracts on in vitro methanogenesis, enzymeactivities and fermentation of feed in rumen liquorof buffalo. Animal Feed Science and Technology, 128,276–291.

Patra, A. K., Kamra, D. N., & Agarwal, N. (2006b). Effectof plants containing secondary metabolites on in vitromethanogenesis, enzyme profile and fermentation offeed with rumen liquor of buffalo. Animal Nutritionand Feed Technology, 6, 203–213.

Patra, A. K., Kamra, D. N., & Agarwal, N. (2008). Effectof leaf extracts on fermentation of feds and methano-genesis with rumen liquor of buffalo. Indian Journal ofAnimal Science, 78, 91–96.

Patra, A. K., Kamra, D. N., & Agarwal, N. (2010a). Effectsof extracts of spices on rumen methanogenesis, en-zyme activities and fermentation of feeds in vitro.Journal of the Science of Food and Agriculture, 90,511–520.


Patra, A. K., Kamra, D. N., Bhar, R., Kumar, R.,Chaturvedi, V. B., & Agarwal, N. (2010b). Effect ofTerminalia chebula and Allium sativum on nutrientutilization and methane production in sheep. Journalof Animal Physiology and Animal Nutrition, 95, 187–191.

Pen, B., Takaura, K., Yamaguchi, S., Asa, R., &Takahashi, J. (2007). Effects of Yucca schidigera andQuillaja saponaria with or without β-1,4 galacto-oligosaccharides on ruminal fermentation, methaneproduction and nitrogen utilization in sheep. AnimalFeed Science and Technology, 138, 75–88.

Pinares-Patiño, C. S., Ulyatt, M. J., Lassey, K. R., Barry,T. N., & Holmes, C. W. (2003). Persistence ofdifferences between sheep in methane emission undergenerous grazing conditions. Journal of AgriculturalScience, 140, 227–233.

Puchala, R., Min, B. R., Goetsch, A. L., & Sahlu, T. (2005).The effect of a condensed tannin-containing forage onmethane emission by goats. Journal of Animal Science,83, 182–186.

Sahoo, B., Saraswat, M. L., Haque, N., & Khan, M. Y.(1999). Energy balance and methane production insheep fed chemically treated wheat straw. SmallRuminant Research, 35, 13–19.

Santoso, B., Mwenya, B., Sar, C., Gamo, Y., Kobayashi,T., Morikawa, R. et al. (2004). Effects of supplement-ing galacto-oligosaccharides, Yucca schidigera andnisin on rumen methanogenesis, nitrogen and energymetabolism in sheep. Livestock Production Science,91, 209–217.

Sar, C., Santoso, B., Gamo, Y., Kobayashi, T., Shiozaki, S.,Kimura, K. et al. (2004a). Effects of combination ofnitrate with β-1,4 galacto-oligosaccharides and yeast(Candida kefyr) on methane emission from sheep.Asian-Australasian Journal of Animal Sciences, 17,73–79.

Sar, C., Santoso, B., Mwenya, B., Gamo, Y., Kobayashi, T.,Morikawa, R. et al. (2004b). Manipulation of rumenmethanogenesis by the combination of nitrate with β-1,4 galacto-oligosaccharides or nisin in sheep. AnimalFeed Science and Technology, 115, 129–142.

Sar, C., Mwenya, B., Pen, B., Morikawa, R., Takaura, K.,Kobayashi, T. et al. (2005). Effect of nisin on ruminalmethane production and nitrate/nitrite reduction invitro. Australian Journal of Agricultural Research, 56,803–810.

Sauer, F. D., Fellner, V., Kinsman, R., Kramer, J. K.,Jackson, H. A., Lee, A. J. et al. (1998). Methane out-put and lactation response in Holstein cattle with mo-nensin or unsaturated fat added to the diet. Journal ofAnimal Science, 76, 906–914.

Singh, G. P. (2001). Livestock production and environ-mental protection. In Proceedings of the 10th AnimalNutrition Conference (pp. 211–221), National DairyResearch Institute, Karnal, Haryana, India.

Sirohi, S., Michaelowa, A., & Sirohi, S. K. (2007). Mitiga-tion options for enteric methane emissions from dairyanimals: An evaluation for potential CDM project inIndia. Mitigation and Adaptation Strategies for GlobalChange, 12, 259–274.

Sliwinski, B. J., Solvia, C. R., Machmuller, A., Kreuzer,M. (2002). Efficacy of plant extracts rich in secondaryconstituents to modify rumen fermentation. AnimalFeed Science and Technology, 101, 101–114.

Srivastava, A. K., & Garg, M. R. (2002). Use of sul-fur hexafluoride tracer technique for measurement ofmethane emission from ruminants. Indian Journal ofDairy Science, 55, 36–39.

Steinfeld, H., Costales, A., Rushton, J., Scherf, B., Bennett,T., & Hall, D. (2006). Livestock report 2006. Rome:FAO.

Thornton, J. H., & Owens, F. N. (1981). Monensin supple-mentation and in vivo methane production by steers.Journal of Animal Science, 52, 628–634.

Trei, J. E., Parish, R. C., Singh, Y. K., & Scott G. C. (1972).Effect of methane inhibitors on rumen metabolismand feedlot performance of sheep. Journal of DairyScience, 54, 536–540.

Ulyatt, M. J., Lassey, K. R., Shelton, I. D., & Walker,C. F. (2002). Methane emission from dairy cows andwether sheep fed subtropical grass-dominant pasturesin midsummer in New Zealand. New Zealand Journalof Agricultural Research, 45, 227–234.

Ungerfeld, E. M., Kohn, R. A., Wallace, R. J., & Newbold,C. J. (2007). A meta-analysis of fumarate effects onmethane production in ruminal batch cultures. Journalof Animal Science, 85, 2556–2563.

Van Nevel, C. J., & Demeyer, D. I. (1996). Control of ru-men methanogenesis. Environmental Monitoring andAssessment, 42, 73–97.

Van Vugt, S. J., Waghorn, G. C., Clark, D. A., &Woodward, S. L. (2005). Impact of monensin onmethane production and performance of cows fed for-age diets. Proceedings of the New Zealand Society ofAnimal Production, 65, 362–366.

Waghorn, G. C., Tavendale, M. H., & Woodfield,D. R. (2002). Methanogenesis from forages to sheep.Proceedings of the New Zealand Society of GrasslandAssociation, 64, 167–171.

Waghorn, G. C., Clark, H., Taufa, V., & Cavannagh, A.(2007). Monensin controlled release capsules for im-proved production and mitigating methane in dairycows fed pasture. Proceedings of the New ZealandSociety of Animal Production, 67, 266–271.

Wallace, R. J., Wood, T. A., Rowe, A., Price, J., Yanez,D. R., Williams, S. P. et al. (2006). Encapsulated fu-maric acid as a means of decreasing ruminal methaneemissions. International Congress Series, 1293, 148–151.

Wang, C. J., Wang, S. P., & Zhou, H. (2009). Influencesof flavomycin, ropadiar, and saponin on nutrient di-gestibility, rumen fermentation, and methane emissionfrom sheep. Animal Feed Science and Technology, 148,157–166.

Wedegaertner, T. C., & Johnson, D. E. (1983). Monensineffects on digestibility, methanogenesis and heat in-crement of a cracked corn-silage diet fed to steers.Journal of Animal Science, 57, 168–177.

Wedlock, D. N., Pedersen, G., Denis, M., Dey, D., Janssen,P. H., & Buddle, B. M. (2010). Development of a vac-cine to mitigate greenhouse gas emissions in agricul-


ture: vaccination of sheep with methanogen fractionsinduces antibodies that block methane production invitro. New Zealand Veterinary Journal, 58, 29–36.

Weimer, P. J. (1998). Manipulating ruminal fermentation:a microbial ecological perspective. Journal of AnimalScience, 76, 3114–3122.

Williams, Y. J., Rea, S. M., Popovski, S., Pimm, C. L.,Williams, A. J., Toovey, A. F. et al. (2008). Re-sponses of sheep to a vaccination of entodinal ormixed rumen protozoal antigens to reduce rumen pro-tozoal numbers. British Journal of Nutrition, 99, 100–109.

Wina, E., Muetzel, S., Hoffmann, E., Makkar, H. P. S., &Becker, K. (2005). Saponins containing methanol ex-tract of Sapindus rarak affect microbial fermentation,microbial activity and microbial community structurein vitro. Animal Feed Science and Technology, 121,159–174.

Woodward, S. L., Waghorn, G. C., Ulyatt, M. J., & Lassey,K. R. (2001). Early indication that feeding lotus willreduce methane emission from ruminants. Proceed-

ings of the New Zealand Society of Animal Production,61, 23–26.

Woodward, S. L., Waghorn, G. C., Lassey, K. R.,& Laboyrie, P. G. (2002). Does feeding sulla(Hedysarum coronarium) reduce methane emissionfrom dairy cows? Proceedings of the New ZealandSociety of Animal Production, 62, 227–230.

Wright, A. -D. G., Kennedy, P., O’Neill, C. J., Toovey,A. F., Popovski, S., Rea, S. M. et al. (2004). Reducingmethane emission in sheep by immunization againstrumen methanogens. Vaccine, 22, 3976–3985.

Yuan, Z. P., Zhang, C. M., Zhou, L., Zou, C. X., Guo,Y. Q., Li, W. T., et al. (2007). Inhibition of methano-genesis by tea saponin and tea saponin plus dis-odium fumarate in sheep. Journal of Animal and FeedSciences, 16(Supplement 2), 560–565.

Zhou, M., Hernandez-Sanabria, E., & Guan, L. L. (2009).Assessment of the microbial ecology of ruminalmethanogens in cattle with different feed efficiencies.Applied and Environmental Microbiology, 75, 6524–6533.

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Enteric methane mitigation technologies for …...Environ Monit Assess (2012) 184:1929–1952 DOI 10.1007/s10661-011-2090-y Enteric methane mitigation technologies for ruminant livestock: