by Grace Stockmal
Greenhouse gases (GHG), specifically methane, carbon dioxide, and nitrous oxide, contribute to eutrophication and global warming. Large amounts of these gases are released by beef and dairy farms. The misconception is how and why greenhouse gases are emitted from cows. It is hypothesized that greenhouse gas emissions from cattle can be reduced through mitigation strategies in beef and dairy production along with farmers’ contributions to their livestock’s emissions. The reduction of emissions and increase in milk production comes from increased activity and care of the cows, including medicating lesions and diseases. It is also concluded that waste management and records of emissions support the general public in renewable energy, better quality beef and dairy for sale, and a reduced progression of global warming. These results can add to future methods for climate control, alternatives to beef and dairy, and farm maintenance of all livestock.
Key Words: mitigation, enteric fermentation, methanogens, biogas, cattle lameness, carbon footprint
Greenhouse gases (GHG) contribute to climate change by depleting the ozone layer and changing the planet’s environment. Some of these gases are emitted from dairy and beef farms due to biological functions of the cattle. Methane, nitrous oxide, and carbon dioxide are the most common greenhouse gases released from cows1; methane comes from the release of gas during digestion while carbon dioxide and nitrous oxide are found in manure1. Cows contribute to GHG emissions in the agricultural industry due to rumination. They digest complex starches with a natural process of fermentation in their rumen called enteric fermentation2, resulting in the highest impact on methane production in the gastrointestinal tract. Problems also arise in the lactation process of dairy cows3 and the intensive growth of muscle in beef cattle1. Cattle in farms that are fed a main diet of grain increase emissions from rumination and lead to reduced muscle production4. While this diet may be cheaper and easier for the farmer, it leads to health issues and lack of activity for the cows, resulting in conditions like subclinical mastitis and foot lesions. These health issues in the cows increase GHG emissions and impact global warming and the environment overall.
The future of the atmosphere, temperature, and water conditions on this planet depend on reduced greenhouse gas emissions and a reduction in the environmental hazards of mass production of beef and dairy5. Almost 40% of carbon dioxide emissions in Latin America are due to their cow pastures1. Some solutions to mitigate these emissions are available for farmers, including a carbon footprint calculator and milk recording. These tools can help current farmers understand their own impact to GHG emissions and assist scientists’ future research developments of more useful mitigation strategies and possible ways to raise cattle with reduced GHG emissions. The future of this research can also include developing alternatives to beef and dairy that may reduce the demand for cows and result in a healthier lifestyle for the livestock. There are gaps in the field regarding the measured GHG in the atmosphere, along with the recorded emissions from the farms themselves. The technology to study cattle emissions is limited, and thus prevents accurate studies of GHG emitted worldwide. It is essential to reduce these emissions to prevent a higher concentration of GHG in the atmosphere.
Source of the Gases
Of all greenhouse gases emitted by dairy cows on farms, 62-65% of emissions are reported to be methane from digestion1. Cows have a complex digestive system which involves their rumen, the first compartment of their stomach where enteric fermentation occurs, as seen in Figure 1. Methanogens, a species of microbial gut bacteria, live in the rumen and are responsible for fermenting plant material and producing methane6. While many farmers find it cost-effective to use a grain-based diet, it is more harmful to the cows and the environment. A diet consisting of primarily grains or complex carbohydrates increases methane release. A cow’s digestive system is built to break down omega-3 fatty acids and simple starches in grass, but the introduction of grain, including corn and soy, to their diet has only lengthened the process of digestion and led to an increase in the release of methane7. Due to increased digestion time, beef cattle experience a reduction in muscle production since most of their diet is broken down to methane4. The methanogens impact the digestion process, which limits the food contribution to muscle growth and an increase in methane release.
One solution offered was isolating the genome sequence in methanogens and working on modifying it to release less methane during enteric fermentation6. Through modification, this would allow for cows to continue to eat grains and release less methane while digesting. Another solution is for farmers to treat their cows in an ethical way. This is crucial in order to ensure comfort in the cows, increase their physical health8, and abide by worldwide policies on livestock treatment9. Ethical treatment involves a proper diet and land for cows to be active. If farmers could provide more grassy land for their cows to roam and eat, the release of methane for the farm overall would reduce.
Cow manure breaks down into carbon dioxide and nitrous oxide in the soil10, which contribute to pollution by runoff. This leads to eutrophication in the local water and releases greenhouse gases from the algae produced by pollution11. One solution to reducing the amount of manure in the soil is to utilize biogas. Biogas has emerged as a popular process on dairy farms that can be a renewable energy source through the collection and burning of manure2, 12. Not only is it a cheaper form of energy, but it was found to mitigate 60% of GHG emissions annually in two cities in northern Italy13. Burning the manure instead of allowing it to infiltrate the soil will reduce the carbon dioxide and nitrous oxide present while providing a new form of renewable energy. If the gases never make it to the ground, then there will be a reduction in pollution and eutrophication of local water.
Medical Impacts on GHG Emissions/ Treatment
One component of farm-raised cattle is promoting active lifestyles for the cows to ensure prime health. Dairy cows who are not as active or do not have accessibility to roam are more likely to suffer medical ailments, produce less milk, and have higher GHG emissions14-15. The largest problem in cattle lameness is informing the farmers; 8-25% of cattle lameness goes undetected due to farmers overestimating the activity of their cows16. Two specific diseases caused by cattle lameness are subclinical mastitis15 and foot lesions14.
Subclinical mastitis is a bacterial infection of the udders from the staphylococci pathogen17. It clogs the milk ducts, reduces milk released, and causes an increase of methane due to higher somatic cell counts in the infected areas15. One issue with subclinical mastitis is its ability to be resistant to antimicrobials, especially when a large number of the herd has the disease17. The most effective solution to treat subclinical mastitis is medicating with alternating antibiotics18 and udder injections17. This medication method treats the infections, prevents the spread to more of the herd, and allows for a larger supply of milk per cow.
Digital dermatitis, or foot lesions, are ulcers that appear on the bottom of the toes when the cows are inactive for long periods of time14, 19. As seen in Figure 1, the toes are hidden under the hooves and are highly susceptible to injury due to exposure. In an experiment of 204 herds, 96.7% of the herds were affected by digital dermatitis19. When the cattle are in pain, they produce less milk and release more methane in times of bodily stress14. The solutions to foot lesions are treating them medically and increasing activity of the cows by access to pastures or open land16. This will reduce the stress, allow for a healthier lifestyle, and overall reduce GHG emissions.
Methods for Efficient Farming
One component of these farms is their carbon footprint, a number recorded per unit, that collects every environmental impact from the farm, including GHG emissions, and pollution of the world’s air and water. This number per farm is usually not known, which puts farmers at risk for releasing more GHG than they are aware of. One mitigation strategy offered is a carbon footprint calculator, which calculates the footprint based on these direct and indirect GHG emissions from farms20. This calculator allows farmers to see the actual number of GHG being released and use other mitigation strategies to reduce this number. For example, the average carbon footprint for milk in New Zealand dropped from 0.81 to 0.75 kg of carbon dioxide equivalent from the years 2010 to 2018 once limitations on farms were enacted10. This calculator will allow all farmers to record their GHG emissions and modify their personal mitigation strategies on their farms.
Another sustainable farming solution is a process called milk recording. This is a use of a machine commonly in agriculture that measures milk through samples and provides records of quality and properties21. This technique allows farmers to evaluate their milk samples and make changes based on the health of their livestock. For example, a milk record from an Irish farm predicted a 9% increase in GHG emissions based on the production of milk per cow and the quality of the milk21. Milk recording can provide accurate data on the quality of milk and its contribution to GHG emissions. It was found that organic milk has 40% less GHG emissions than mass-produced milk on other farms22. This method of milk recording can allow all farmers to see a report of their milk quality and production and alter their mitigation strategies to farm effectively and sustainably.
Raising cows for beef and dairy in mass numbers results in some of the largest emissions of greenhouse gases in agriculture. Cows experience high methane emissions due to enteric fermentation and a diet with prolonged digestion. Solutions include a primarily grass diet for the cattle or gene modification of the methanogens. A solution to soil saturated with carbon dioxide and nitrous oxide from cow manure is to increase popularity of biogas beyond farms.
Many health problems in beef and dairy cows go unnoticed and tend to lead to higher emissions and a reduced production of milk15, which can be solved with consistent records, prevention of lameness, and medical attention to diseases. Routine veterinarian exams and sufficient room for cattle activity can prevent subclinical mastitis and foot lesions in the herd. The demand for beef and dairy creates a struggle for farmers trying to profit off of their farm while still maintaining proper treatment of their animals and the environment. A method for monitoring GHG emissions is an official recording of their carbon footprint and milk recording while also practicing mitigation strategies and avoiding mass production of beef and dairy.
Future research in GHG emissions from cattle can branch off into environmental sustainability or alternates to dairy and beef in the food industry. There can be more research into solutions of raising cattle to reduce methane emissions along with more research in proper waste management12. Research can also advance in substitutes for dairy and beef demand, including synthetic meat, to introduce the general population to more plant-based lifestyles. This would allow for farmers to avoid mass production and offer more ethical ways to raise cattle. These advancements in research can lead to greater reduction of greenhouse gas emissions, a healthier environment for all, and the reduced production of cattle for the beef and dairy industry.
(1) Bilotto, F.; Recavarren, P.; Vibart, R.; Machado, C. F. Backgrounding strategy effects on farm productivity, profitability and greenhouse gas emissions of cow-calf systems in the Flooding Pampas of Argentina. Agricultural Systems 2019, 176, 102688, DOI: https://doi.org/10.1016/j.agsy.2019.102688.
(2) Ersoy, E.; Ugurlu, A. The potential of Turkey’s province-based livestock sector to mitigate GHG emissions through biogas production. Journal of Environmental Management 2020, 255, 109858, DOI: https://doi.org/10.1016/j.jenvman.2019.109858.
(3) Bittante, G.; Bergamaschi, M. Enteric methane emissions of dairy cows predicted from fatty acid profiles of milk, cream, cheese, ricotta, whey, and scotta. Animals 2020, 10 (1), DOI: 10.3390/ani10010061.
(4) Wiedemann, S.; Davis, R.; McGahan, E.; Murphy, C.; Redding, M. Resource use and greenhouse gas emissions from grain-finishing beef cattle in seven Australian feedlots: A life cycle assessment. Animal Production Science 2017, 57 (6), 1149-1162, DOI: 10.1071/AN15454.
(5) Mariantonietta, F.; Alessia, S.; Francesco, C.; Giustina, P. GHG and cattle farming: CO-assessing the emissions and economic performances in Italy. Journal of Cleaner Production 2018, 172, 3704-3712, DOI: https://doi.org/10.1016/j.jclepro.2017.07.167.
(6) Leahy, S. C.; Kelly, W. J.; Altermann, E.; Ronimus, R. S.; Yeoman, C. J.; Pacheco, D. M.; Dong, L.; Zhanhao, K.; McTavish, S.; Sang, C.; Lambie, S. C.; Janssen, P. H.; Dey, D.; Attwood, G. T. The Genome Sequence of the Rumen Methanogen Methanobrevibacter ruminantium Reveals New Possibilities for Controlling Ruminant Methane Emissions. PLoS ONE 2010, 5 (1), 1-17, DOI: 10.1371/journal.pone.0008926.
(7) Koneswaran, G.; Nierenberg, D. Global Farm Animal Production and Global Warming: Impacting and Mitigating Climate Change. Environmental Health Perspectives 2008, 116 (5), 578-582, DOI: 10.1289/ehp.11034.
(8) Odongo, N. E.; Bagg, R.; Vessie, G.; Dick, P.; Or-Rashid, M. M.; Hook, S. E.; Gray, J. T.; Kebreab, E.; France, J.; McBride, B. W. Long-Term Effects of Feeding Monensin on Methane Production in Lactating Dairy Cows. Journal of Dairy Science 2007, 90 (4), 1781-1788, DOI: https://doi.org/10.3168/jds.2006-708.
(9) York, L.; Heffernan, C.; Rymer, C. A systematic review of policy approaches to dairy sector greenhouse gas (GHG) emission reduction. Journal of Cleaner Production 2018, 172, 2216-2224, DOI: https://doi.org/10.1016/j.jclepro.2017.11.190.
(10) Ledgard, S. F.; Falconer, S. J.; Abercrombie, R.; Philip, G.; Hill, J. P. Temporal, spatial, and management variability in the carbon footprint of New Zealand milk. J Dairy Sci 2020, 103 (1), 1031-1046, DOI: 10.3168/jds.2019-17182.
(11) Payen, S.; Falconer, S.; Carlson, B.; Yang, W.; Ledgard, S. Eutrophication and climate change impacts of a case study of New Zealand beef to the European market. Sci Total Environ 2019, 710, 136120, DOI: 10.1016/j.scitotenv.2019.136120.
(12) Shirzad, M.; Kazemi Shariat Panahi, H.; Dashti, B. B.; Rajaeifar, M. A.; Aghbashlo, M.; Tabatabaei, M. A comprehensive review on electricity generation and GHG emission reduction potentials through anaerobic digestion of agricultural and livestock/slaughterhouse wastes in Iran. Renewable and Sustainable Energy Reviews 2019, 111, 571-594, DOI: https://doi.org/10.1016/j.rser.2019.05.011.
(13) Bartoli, A.; Hamelin, L.; Rozakis, S.; Borzęcka, M.; Brandão, M. Coupling economic and GHG emission accounting models to evaluate the sustainability of biogas policies. Renewable and Sustainable Energy Reviews 2019, 106, 133-148, DOI: https://doi.org/10.1016/j.rser.2019.02.031.
(14) Mostert, P. F.; van Middelaar, C. E.; de Boer, I. J. M.; Bokkers, E. A. M. The impact of foot lesions in dairy cows on greenhouse gas emissions of milk production. Agricultural Systems 2018, 167, 206-212, DOI: https://doi.org/10.1016/j.agsy.2018.09.006.
(15) Özkan Gülzari, Ş.; Vosough Ahmadi, B.; Stott, A. W. Impact of subclinical mastitis on greenhouse gas emissions intensity and profitability of dairy cows in Norway. Preventive Veterinary Medicine 2018, 150, 19-29, DOI: https://doi.org/10.1016/j.prevetmed.2017.11.021.
(16) Dutton-Regester, K. J.; Wright, J. D.; Rabiee, A. R.; Barnes, T. S. Understanding dairy farmer intentions to make improvements to their management practices of foot lesions causing lameness in dairy cows. Preventive Veterinary Medicine 2019, 171, 104767, DOI: https://doi.org/10.1016/j.prevetmed.2019.104767.
(17) Bolte, J.; Zhang, Y.; Wente, N.; Kromker, V. In Vitro Susceptibility of Mastitis Pathogens Isolated from Clinical Mastitis Cases on Northern German Dairy Farms. Vet Sci 2020, 7 (1), DOI: 10.3390/vetsci7010010.
(18) Poizat, A.; Bonnet-Beaugrand, F.; Rault, A.; Fourichon, C.; Bareille, N. Antibiotic use by farmers to control mastitis as influenced by health advice and dairy farming systems. Preventive Veterinary Medicine 2017, 146, 61-72, DOI: https://doi.org/10.1016/j.prevetmed.2017.07.016.
(19) Cramer, G.; Lissemore, K. D.; Guard, C. L.; Leslie, K. E.; Kelton, D. F. Herd- and Cow-Level Prevalence of Foot Lesions in Ontario Dairy Cattle. Journal of Dairy Science 2008, 91 (10), 3888-3895, DOI: https://doi.org/10.3168/jds.2008-1135.
(20) Galloway, C.; Conradie, B.; Prozesky, H.; Esler, K. Opportunities to improve sustainability on commercial pasture-based dairy farms by assessing environmental impact. Agricultural Systems 2018, 166, 1-9, DOI: https://doi.org/10.1016/j.agsy.2018.07.008.
(21) Balaine, L.; Dillon, E. J.; Läpple, D.; Lynch, J. Can technology help achieve sustainable intensification? Evidence from milk recording on Irish dairy farms. Land Use Policy 2020, 92, 104437, DOI: https://doi.org/10.1016/j.landusepol.2019.104437.
(22) Flysjö, A.; Cederberg, C.; Henriksson, M.; Ledgard, S. The interaction between milk and beef production and emissions from land use change – critical considerations in life cycle assessment and carbon footprint studies of milk. Journal of Cleaner Production 2012, 28, 134-142, DOI: https://doi.org/10.1016/j.jclepro.2011.11.046.