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Can livestock farming reduce its emissions?

How to reduce methane emissions from livestock farming?

Anaïs Marechal, science journalist
On April 6th, 2022 |
4 mins reading time
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How to reduce methane emissions from livestock farming?
cecile_martin
Cécile Martin
Research Director in Animal Science at Inrae    
Key takeaways
  • According to the FAO, in 2010 livestock farming was responsible for the emission of 8.1 billion tonnes (Gt) of CO2 equivalent, mainly due to cattle farming (62% of the sector's emissions).
  • This sector has ways that it could use to reduce its footprint: enteric fermentation (44% of global livestock emissions), animal feed (41%) and manure management (10%).
  • Emissions are linked to our consumption. The larger the animal, the more feed it consumes and the more methane it produces. A cow emits about 600 L of CH4 per day, compared to 60 L for a sheep.
  • A feed additive known to be anti-methanogenic could help reduce 3-NOP. Studies show that it has the potential to reduce CH4 production by 20-40%.

Accord­ing to the FAO, in 2010 live­stock farm­ing was respon­si­ble for the emis­sion of 8.1 bil­lion tonnes (Gt) of CO2 equiv­a­lent, main­ly due to cat­tle farm­ing (62% of the sec­tor’s emis­sions)1. Of course, reduc­ing these emis­sions depends pri­mar­i­ly on con­sumers” food choic­es. But the sec­tor also has a num­ber of means of reduce its cli­mate impact: the mit­i­ga­tion poten­tial is esti­mat­ed at 2.5 Gt CO2 equiv­a­lent, or 33% for con­sis­tent pro­duc­tion. These levers are based on the sec­tor’s three main emis­sion sources: enteric fer­men­ta­tion (44% of glob­al live­stock emis­sions), ani­mal feed (41%) and manure man­age­ment (10%), accord­ing to the FAO.

Enteric fer­men­ta­tion takes place in the rumen of rumi­nants (cat­tle, sheep, and goats), dur­ing the trans­for­ma­tion of food into nutri­ents. It pro­duces methane (CH4), belched out by the ani­mals (burps and not farts, as leg­end has it). It is the main GHG emit­ted by live­stock farm­ing, which is respon­si­ble for one third of anthro­pogenic CH4 emis­sions2. Reduc­ing methane emis­sions (from all sources) is one of the pri­or­i­ties of the EU, which adopt­ed a methane strat­e­gy in Octo­ber 2020 as part of the glob­al objec­tive of a 50% reduc­tion by 2050.

Methane emis­sions from live­stock are rel­a­tive­ly sta­ble in Europe and low com­pared to Asia, South Amer­i­ca, and Africa. In these regions, they are increas­ing due to pop­u­la­tion growth and thus the size of the herd. Chi­na and India are the largest emitters.

Means of reducing emissions

It is impor­tant to under­stand that emis­sions are direct­ly linked to our food con­sump­tion. Cat­tle (dairy or beef) are the biggest emit­ters: the big­ger the ani­mal, the more food it con­sumes and the more methane it pro­duces. A cow emits about 600L of CH4 per day, com­pared to 60L for a sheep. These emis­sions are attract­ing the atten­tion of the indus­try: reduc­ing them is of nutri­tion­al inter­est to the ani­mal and envi­ron­men­tal inter­est to humans.

There are var­i­ous ways of reduc­ing methane pro­duc­tion in rumi­nants, start­ing with the feed ration. In the rumen, cer­tain micro-organ­isms break down car­bo­hy­drates (cel­lu­lose, starch, etc.). This reac­tion leads to the pro­duc­tion of gas­es, includ­ing hydro­gen, which is con­vert­ed into methane by oth­er micro-organ­isms. In order to reduce CH4 pro­duc­tion, the pro­duc­tion of hydro­gen can be reduced or used in ways oth­er than to form CH4.

Some means are well known and used by farm­ers. Increas­ing the amount of starch in the ration (more cere­als), with­out exceed­ing a cer­tain thresh­old, favours cer­tain micro-organ­isms that pro­duce lit­tle hydro­gen. CH4 emis­sions can be reduced by 10–20% for con­sis­tent pro­duc­tion. Increas­ing lipids in the ration (thanks to sun­flower, rape­seed, flax, etc.) increas­es ani­mal per­for­mance and offers the same poten­tial to reduce CH4. Final­ly, the more digestible the for­age, the less CH4 the ani­mal pro­duces, even if the poten­tial reduc­tions from this are low­er. Cer­tain species rich in tan­nins, such as chico­ry, plan­tain or sain­foin, can also be intro­duced into tem­po­rary grass­land: they reduce CH4 emis­sions but also nitroge­nous dis­charges.3

How­ev­er, these means of mit­i­ga­tion must be con­sid­ered on a broad­er scale. While the con­sump­tion of cere­als reduces the ani­mal’s CH4 emis­sions, the cul­ti­vat­ed sur­faces store less car­bon than per­ma­nent grass­lands. And these crops emit GHGs dur­ing trans­port. The com­pe­ti­tion between human and ani­mal feed should also be considered.

Can certain additives reinforce these effects?

The first syn­thet­ic food addi­tive recog­nised as anti-methanogenic, 3‑NOP, was autho­rised in Feb­ru­ary 2022 in the Euro­pean Union. It acts on one of the enzymes respon­si­ble for methano­gen­e­sis in the rumen: stud­ies show that it has the poten­tial to reduce CHpro­duc­tion by 20–40%. It has been shown to be safe for ani­mals and humans and does not affect pro­duc­tiv­i­ty. How­ev­er, this prod­uct has a cost, and offers no direct ben­e­fit to the farmer: it is essen­tial that the efforts of farm­ers to reduce their GHG emis­sions are rewarded.

Nitrates, which have feed ingre­di­ent sta­tus, reduce CHpro­duc­tion by cap­tur­ing hydro­gen in the rumen and con­vert­ing it to nitrite. They are effec­tive in reduc­ing CH4, but com­pli­cat­ed to use and have a sig­nif­i­cant envi­ron­men­tal impact. Many oth­er addi­tives of nat­ur­al ori­gin are being stud­ied: for exam­ple, we are work­ing with a pro­duc­er of wild plants from Auvergne and are cur­rent­ly test­ing some of them in vivo

Genetics or biotechnology to reduce emissions

Genet­ic selec­tion of ani­mals is high­ly devel­oped for the cat­tle indus­try (espe­cial­ly dairy) and is start­ing to be devel­oped in sheep farm­ing. For the same diet, some ani­mals emit less CHthan oth­ers. The dif­fer­ence is small, less than 10%, but this is not neg­li­gi­ble on a glob­al scale. It has now been estab­lished that this trait is repeat­able with dif­fer­ent diets, and hered­i­tary: this makes it pos­si­ble to envis­age long-term effects of genet­ic selec­tion. How­ev­er, it is not just a ques­tion of con­sid­er­ing the ani­mal’s methanogenic poten­tial: today, research is inter­est­ed in a range of traits, such as pro­duc­tion, health, etc. We need to find the best com­pro­mise for select­ing lines.

As far as biotech­nol­o­gy is con­cerned, sev­er­al avenues are being explored to direct­ly manip­u­late the micro­bial flo­ra of cat­tle. New Zealand is at the fore­front of cre­at­ing a vac­cine against methanogenic micro-organ­isms. An ini­tial tri­al showed poten­tial to reduce methano­gen­e­sis, but to date this has not been replicated.

A study4 also sug­gests that it is pos­si­ble to manip­u­late the micro­bio­ta using the feed addi­tive 3‑NOP: in young cat­tle sup­ple­ment­ed for a few weeks, a per­sis­tent effect was mea­sured up to one year after the sup­ple­men­ta­tion was stopped. These results also need to be repro­duced and mon­i­tored in the longer term.

Priorities for accelerating mitigation 

One of the approach­es stud­ied is to com­bine tools: we assume that the effects are cumu­la­tive. We have demon­strat­ed this with the com­bined use of flax and nitrates, which enhances the reduc­tion of CHemis­sions by affect­ing both the pro­duc­tion and use of hydrogen.

It is also very impor­tant to improve pro­duc­tiv­i­ty, which ben­e­fits the cli­mate and the farm­ers. Many poten­tial solu­tions exist at the herd man­age­ment lev­el: reduc­ing the age of first calv­ing, improv­ing health, and reduc­ing the turnover rate of ani­mals to reduce the unpro­duc­tive peri­od. Chang­ing the feed ration, which is ben­e­fi­cial for CHemis­sions, also increas­es pro­duc­tiv­i­ty to a cer­tain extent. Improv­ing pro­duc­tiv­i­ty is an inter­est­ing strat­e­gy for high emit­ting coun­tries where ani­mals are often low producers. 

1Accord­ing to the Glob­al Live­stock Envi­ron­men­tal Assess­ment Mod­el of the Food and Agri­cul­ture Orga­ni­za­tion of the Unit­ed Nations (accessed on 15 March 2022: https://​www​.fao​.org/​g​l​e​a​m​/​r​e​s​u​l​t​s/fr/)
2Jack­son, R.B., et al., 2020, Increas­ing anthro­pogenic methane emis­sions arise equal­ly from agri­cul­tur­al and fos­sil fuel sources, Env­i­ron. Res. Lett. 15 071002
3Mar­tin, C., et al. 2021. The use of plant bioac­tive com­pounds to reduce green­house gas emis­sions from farmed rumi­nants. http://​dx​.doi​.org/​1​0​.​1​9​1​0​3​/​A​S​.​2​0​2​0​.​0​0​77.13
4Meale, S. J., et al., 2021, Ear­ly life dietary inter­ven­tion in dairy calves results in a long-term reduc­tion in methane emis­sions, Sci­en­tif­ic Reports, 11:3003