The narrative surrounding the environmental cost of producing milk and beef often paints a bleak picture. Because it is more palatable to dictate a reduction in meat and milk consumption to enact environmental change than to reduce fossil fuel use for transportation, agriculture is tasked to solve global climate change and greenhouse gas emissions.
Farmers often must bear the financial burden of mitigating the environmental footprint of producing food. What is the true carbon footprint of producing milk and meat, and what can we do to make our animals more sustainable?
Agriculture accounts for 9 percent of the total anthropogenic (associated with human activity) greenhouse gas emissions in the U.S. The primary sources of agricultural greenhouse gases are artificial fertilizer application to crops, enteric fermentation (digestion of feed in the rumen) and manure storage.
The trends for the last 60 years have seen animal agriculture produce more food for human consumption with fewer farms and fewer animals. In fact, the carbon footprint of milk per unit has been reduced due to improved efficiency.
Compared to dairy production figures from 1944, producing milk in 2007 required 21 percent of animals, 23 percent of feed, 35 percent of water and 10 percent of land to produce the same amount of milk.
Greenhouse gas emissions related to milk production have also decreased when comparing 1944 to 2007, with a 43 percent drop in methane and a 56 percent drop in nitrous oxide per pound of milk.
The Innovation Center for U.S. Dairy has set forth industry initiatives to reduce the carbon footprint of producing milk by 25 percent by 2020, largely focusing on methane emissions. Why should the dairy industry care about methane emissions from cattle?
Retailers and consumers are concerned with the greenhouse gas emissions associated with producing milk and beef. Most international policy and attention is focused on non-carbon dioxide emissions (such as methane and nitrous oxide) since they are easier and cheaper to mitigate than carbon dioxide emissions.
In addition, reducing methane emissions can be financially advantageous, as it can result in improved milk production and efficiency. Enteric and manure methane represent more than 40 percent of the carbon footprint of milk produced in the U.S., which makes methane emissions a large target for mitigation.
Enteric methane, in particular, can be addressed by the types of feedstuffs we feed ruminants. Reducing carbon emissions by nutritional strategies should focus on feeding high-quality, digestible forages and other concentrates. This strategy reduces the carbon footprint by changing rumen fermentation patterns and how the rumen microbes extract energy from feed.
This leads to fermentation end products that do not require the formation of methane as well as supporting increased milk production and efficiency.
Dietary changes aimed at reducing methane emissions from cattle must be ones that do not negatively impact rumen fermentation, digestibility or milk production. Feed additives that reduce methane formation can provide a small but important reduction in methane emissions that cannot be achieved by nutrition or genetic and management practices.
Using additives that directly mitigate methane emissions from the rumen should be considered with caution; some compounds effectively reduce methane formation but are also toxic to rumen microbes. In addition, the ability of the rumen microbiome to adapt to a compound can reduce the efficacy of that compound.
All these factors are important when selecting a feed additive to reduce methane emission from the rumen.
There are a number of compounds that have been found to reduce methane formation in the rumen with various modes of action. Inhibitors, such as 3-nitrooxypropanol (3NP), are chemicals that selectively inhibit rumen methanogen microbes that produce methane in the rumen.
Research has shown 3NP can reduce methane by 59 percent, and this reduction persisted over a 112-day feeding period, making 3NP a promising tool for reducing methane.
Alternative electron acceptors, such as nitrates, alter the biochemistry of the rumen to allow for the formation of ammonia/ammonium (NH3/NH4+), which rumen microbes can use as a nitrogen source for growth, instead of methane, which is emitted as a waste gas.
Nitrates have been shown to reduce methane emissions by up to 50 percent with no negative impacts on milk production and have a persistent effect over time.
As with other nitrogen-based feed ingredients, nitrates should be increased in the ration slowly to ensure proper adaptation of the rumen microbiome and to avoid accumulation of potential toxic intermediate products. When fed as part of low-protein rations, nitrates show potential to reduce methane emissions from cattle.
Improving dairy cattle lifetime production is another aspect of improving efficiency and reducing the carbon footprint of producing a gallon of milk. Genetic selection for milk yield, as well as management practices, allow cows to maximize milk production and efficiency.
Management practices include facility and equipment design to maximize cow comfort, ensuring optimal health, maximizing reproductive efficiency and reducing the number of dry cows and replacement heifers.
These strategies seek to maximize productive efficiency on the farm and minimize non-productive animals that add to the carbon footprint without producing milk.
Programs to reduce methane emissions and farm carbon footprints via nutrition and feeds should include the following strategies:
- Focus on feeding digestible feeds that maximize animal production and efficiency.
- Directly reduce methane emissions with rumen modifiers that alter the biochemistry of the rumen or selectively inhibit methane-producing microbes in the rumen.
- Increase animal production by management or genetics to dilute maintenance energy requirement, thereby increasing feed efficiency through optimal nutrition and animal management.
As a company that provides comprehensive carbon audits and calculates total farm carbon footprints, we surveyed 58 farms in Europe to gather carbon footprint information. After identifying areas for improvement in milk production, animal health and reproduction, management and nutritional changes were implemented on these farms.
Upon re-evaluation after six months, the farms averaged 2 pounds increase in milk, four fewer days open and reduced incidence of mastitis, metritis and lameness while reducing total (overall) greenhouse gas emissions by 2.8 pounds per cow per day.
Between increased milk yield and improved fertility and health, farm profits were estimated to increase by $253 per cow.
Profitability and sustainability are not conflicting goals for the dairy and beef industry. Farms that are efficient and environmentally sustainable are also the same farms that are high-producing and profitable.
By adopting new feed additives based on scientific research, modern farming techniques identifying areas of waste within farm and animal management, and feeding a high-quality balanced ration to their cattle, farmers are maximizing their farms’ profitability while minimizing environmental impact. 
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Amanda Gehman
- Research Project Manager
- Alltech
