Methane Emissions in Dairy Farming
Methane (CH4) is a green house gas (GHG) – it traps infra-red (IF) radiation in the earth’s atmosphere, contributing to rising global temperatures. It is the second most abundant GHG in the atmosphere after carbon dioxide (CO2) produced from fossil fuel combustion. Methane exists in the atmosphere for less time than CO2 but it traps more IF radiation[1].
Enteric fermentation is a process that occurs during digestion in animals, particularly ruminants such as cows, in which microbes within the digestive system break down (ferment) animal feed into soluble products (acetate, propionate and butyrate) that can be distributed and used around the animal for milk or meat production[2]. The by-product of enteric fermentation is methane – cattle and sheep lose between 2 and 10% of their feed energy in the form of methane gas[3]. Contrary to popular belief, most of the emissions from the cattle are from belching or exhaling, rather than from their behind. Cattle manure, especially when poorly managed, is also a large contributor to CH4 emissions. CH4 is produced during the anaerobic decomposition of organic material in the manure by microorganisms, which usually occurs in slurry or liquid manure.
It has been reported that around 14.5% of man-made GHG emissions come from livestock production[4] with 30% of total livestock emissions coming from milk production alone[5]. As the world population increases, the demand for milk and meat will increase as well, indicating an urgent to need to reduce the amount of methane produced by cattle.
Research into Reducing Methane Production in Dairy Farming
1. Genetics
Currently, research is being conducted into using genetics to reduce methane emissions from dairy cows. The focus on is on reducing the amount of CH4 produced per litre of energy corrected milk.
It has been found that animals under the same conditions and with the same feed have different methane production, indicating that although the type and quality of feed does play a role, it is primarily physical traits of the cow that affect the amount of methane a cow will produce – traits that can probably be controlled by genetic manipulation. However, it is important to ensure that the genes that reduce methane production do not also affect milk and meat production[6] before you play with them, i.e. you do not want low methane production to relate to low milk and/or meat production.
There are indications that the rumen size and retention time, as well as feed passage rate, affect the level of CH4 production from dairy cows by benefiting certain microbial community structures in the rumen – it is thought that the archaeal and bacterial structure in the rumen have the greatest effect on the amount of methane produced. Archaeal abundance is controlled by host genetics, and thus it should be possible to optimise ruminal conditions to give bacterial communities that will produce less CH4.
In 2018 three Danish researchers were awarded the Innovation Fund Grand Solution Prize in Denmark for developing a method to reduce methane emitted by cattle using breeding. The study took 4 years and used 2500 cows, primarily Holsteins but also some Red and Jersey cows. The three men succeeded in breeding cows that will reduce methane emissions by 5% which in Denmark alone is equal to 90 000 tonnes less carbon dioxide emissions a year. At the same time they reduced feed consumption by 1% indicating a positive correlation between reduced methane emissions and increased feed efficiency. The findings will be used to develop more climate-friendly cows, the genetics of which can be sold worldwide to reduce global methane emissions from cattle[7].
2. Feed
Certain feed additives can impede the action of the microorganisms that produce methane during the cow’s digestive proves. These additives may be synthetic chemicals such as antibiotics, natural supplements, for example seaweed, and fats and oils.
There is major concern over synthetic chemicals as they may impact human health. However, natural supplements do have plenty of potential as an additive to reduce methane production[8]. An Australian seaweed supplement called FutureFeed has been developed by scientists at CSIRO. This supplement produces a bioactive compound known as bromoform that inhibits a specific enzyme in the rumen of the cow during digestion, preventing the formation of methane. It has been found that FutureFeed can reduce production of enteric methane by greater than 80%[9].
Increasing the level of fat and oils in feed has the most practical potential. Dr Beauchemin in Canada performed a study that found increasing fat by feeding a diet of crushed sunflower, canola or flaxseed or dried corn distillers grain reduced the energy lost as methane by up to 20%. Feeding more grain to cattle will also reduce CH4 emissions, but this is not practical because one would prefer to feed animals high-fibre feeds that cannot be consumed by humans. Corn-based diets and high quality forages result in far fewer methane emissions as compared to barley-based diets[10]. Adding antimicrobials known as Ionophores in carefully controlled concentrations also reduce CH4 emissions by increasing feed efficiency and average weight gain – they alter rumen fermentation patterns by disrupting ion concentration gradients which inhibits normal metabolisms of the microorganisms that decrease digestive efficiency. This means that the beneficial bacteria for digestion can be more active and thus there is an increase in animal energy and food can be used more effectively – less energy is lost as methane[11].
3. Manure Management
Methane is produced when livestock manure is microbially digested under anaerobic conditions. This usually happens when large amounts of wet manure are stored in piles or settlement ponds due to animals being kept in a confined area. To reduce the amount of anaerobic digestion that occurs, and thus the amount of methane produced, there are several measures that farmers can take, including aerating manure piles, spreading manure on fields as fertiliser, and composting[12]. It has been found that reducing the amount of manure stored in liquid form and keeping it in this form for as short a time as possible will drastically reduce the amount of methane produced[13]. As well as this, farmers can capture the methane and use this as biogas on the farm to heat e.g. water for cleaning, and to provide electricity, thus reducing the amount of methane released into the atmosphere, and reducing normal electricity consumption.
Conclusion
There are several actions that can be taken to reduce methane gas emissions on farms, including changing cows’ diet to include better quality forage and more grains and adding certain feed additives that will inhibit the microbial actions that produce methane during enteric fermentation. Farmers can also improve their manure management: reducing the amount of manure stored in liquid form and capturing methane to use for power and heat. Meanwhile, scientists and animal genetic companies around the world continue to study the effect of genetics on low-methane producing cattle, developing animals that have higher feed efficiency and lower methane production so that farmers can purchase genetics to create environmentally-friendly herds.
[1]Methane Emissions from Dairy Cattle, An Overview; University of Wisconsin Extension, Sustainable Dairy Fact Sheet Series. [2] Reducing Enteric Methane for Improving Food Security and Livelihoods, Food and Agriculture Organisation of the United Nations. [3] Genetic Technologies to reduce methane emissions from Australian beef cattle; National Livestock Methane Program Fact Sheet. [4] Tackling Climate Change Through Livestock; A Global Assessment of Emissions and Mitigation Opportunities; Animal Production and Health; Food and Agriculture Organisation of the United Nations. [5]Livestock’s long shadow: Environmental issues and options. Steinfeld H, Gerber P, Wassenaar T, Castel V, Rosales M, Haan CD. Rome, Italy: Food and Agriculture Organization of the United Nations (FAO); 2006. [6]Methane Production in Dairy Cows; Impact of Feed and Rumen Microbiota; Rebecca Danielsson, Department of Animal Nutrition and Management Uppsala, Swedish University of Animal Sciences. [7] Breeding for climate-friendly cows is possible – VikingGenetics focuses on reducing methane emissions at herd level; Viking Genetics Press Release; February 2018. [8] Carbon Farming: Reducing Methane Emissions from Cattle Using Feed Additives; Agriculture and Food; Department of Primary Industries and Regional Development, Government of Western Australia. [9] Case study: FutureFeed; CSIRO.au [10] Reducing Methane Emissions from Livestock; Agriculture and Agri-Food Canada. [11] Practical Antimicrobial Therapeutics; Veterinary Medicine (Eleventh Edition); 2017. [12] Managing Manure to Reduce Greenhouse Gas Emissions; Agriculture and Food; Department of Primary Industries and Regional Development, Government of Western Australia. [13] Report: Changing Manure Management Would Significantly Reduce Dairy Methane Emissions; EDF, Dairy Cares Study.