Pursuing Carbon Neutrality in Livestock Production

 For livestock facilities improving nitrogen circularity, reducing nutrient loss to air and surface waters, and better utilization of manure have been hallmarks of pursuing sustainability. Limiting the release of greenhouse gases has now been added to that list.

 Achieving carbon-neutral livestock production requires implementing strategies to reduce greenhouse gas emissions and offset any remaining emissions. In carbon footprinting, there are three emissions scopes. Scope 1 Emissions are greenhouse gas (GHG) emissions from operations owned or controlled by the livestock producer. For livestock facilities, Scope 1 emissions are enteric fermentation methane emissions and methane and nitrous oxide emissions from manure storage practices. This category would also include emissions from the combustion of propane used to heat livestock buildings or fuel used to power equipment and tractors that handle mortality compost.

 Scope 2 emissions are indirect emissions resulting from the generation of purchased or acquired electricity, steam, heating, or cooling. Typically, livestock fans would be carbon dioxide generated from producing electricity to run building fans and power other electric motors used in the feed delivery system.

 Scope 3 emissions are indirect emissions in the value chain, including upstream and downstream emissions. These, for example, would include greenhouse gas emissions resulting in feed production, including raising corn and soybean, grinding and delivering it to the production facility, and emissions associated with moving livestock or livestock products (milk, eggs) to the processing facility. It could also include carbon costs associated with converting the animal (or animal product) into a salable product at the grocery store.

 While I attempt to break these into neat categories by scope, it can be challenging as integrated livestock facilities that produce feed on-farm for their livestock could be considered Scope 1 emissions.

 Scope 1

1. Manure Management: Implement efficient management practices to minimize methane and nitrous oxide emissions. Anaerobic digestion systems, which convert manure into biogas for energy production, are a primary example. Other options include aeration, acidification, frequent manure removal and application, and diet modification. Techniques primarily focus on reducing methane emissions.
2. Enteric Fermentation: Methane is produced during digestion and fermentation in an animal's digestive tract. Developing feeding strategies that reduce enteric fermentation is an active line of research for dairy cattle, with products such as Monensin and seaweed being suggested.
3. Feed Efficiency: Enhance feed efficiency by utilizing improved nutrition strategies, including formulating balanced diets and adding feed additives. Improved feed efficiency reduces the amount of feed required to produce a unit of meat, thereby lowering emissions associated with feed production. Improved feed efficiency due to improved grinding and, as a result, digestibility has been a key improvement in environmental performance.
4. Genetic Selection: Select swine breeds or genetic lines with higher feed efficiency and lower emissions. Genetic improvements can help reduce swine production's environmental impact over time and have been key in our environmental efficiency gains. .

 Scope 2

1. Energy Efficiency: Improve energy efficiency in swine production facilities by using energy-efficient equipment and optimizing heating, ventilation, and lighting systems. Optimizing use reduces energy consumption and associated emissions. Examples include switching lighting to LED (an increasingly popular approach in poultry housing). Fan staging to increase fan efficiency, installation of VFDs on fans to improve performance, and closely monitoring minimum ventilation requirements to reduce propane demand for maintaining barn temperature.
2. Renewable Energy: Incorporate renewable energy sources such as solar panels, wind turbines, or biogas systems to generate clean energy for powering swine production facilities. Renewable energy can significantly reduce carbon emissions. Many swine farms have started adding solar panels to help generate clean energy, but so do changes in energy supply technologies throughout the state.

Scope 3

1. Nutrient Management: Optimize nutrient management practices to minimize the release of nitrous oxide, a potent greenhouse gas. Nutrient management involves carefully managing the method and timing of manure or synthetic fertilizers application to crops. Considering nutrient content, timing, and soil conditions. Optimizing rate, timing, method, and soil conditions is a huge topic and will continue to be studied.
2. Select feed ingredients from agricultural production practices that result in lower carbon footprints of the supplied materials. Life cycle analysis is helping differentiate how substituting DDGS may impact feed carbon relative to soybean meal. Similarly, future work will need to identify how recycling manure, use of cover crops, and reduced tillage affect yield and greenhouse gas emissions, and the digestibility and livestock performance interact to help inform ingredient selection and inclusion rates. These factors will need to be balanced with price and availability.

Carbon Offsetting

Compensate for any remaining emissions by investing in carbon offset projects. This can involve supporting activities such as reforestation or using trees and grassland around building sites to increase carbon storage, renewable energy projects that reduce emissions beyond the farm, and implementing or participating in carbon capture and storage projects.

Below, estimates of different emissions for a deep pit swine finishing facility (wean to finish). These estimates are meant to be illustrative, may not include all emissions, and won't represent all farms.

 

1. Manure Management: A deep pit swine storage would emit approximately 192 kg CO_2,e/head-year.
2. Enteric Fermentation: IPCC Tier 1 approach estimates 1.5 kg CH₄/hd-year, or 42 kg CO_2,e/head-year.
3. Barn Heat: Harmon et al. (Sizing minimum ventilation to save heating energy in swine housing) estimated usage of 2 gallons per pig space per year, or 11.4 kg CO_2,e/head-year.
4. Barn Electricity Use: Barn design will impact energy use, but around 25 kWh/pig space per year (see Hanna et al., 2016 – Energy use for field operations, crop drying, and swine housing on University Farms). Iowa is estimated to generate 0.36 kg N₂O/MWh and 430.5 kg CO₂/MWh. These emissions are about 0.5 kg CO_2,e/kWh, or 13.5 kg CO_2,e/head-year.
5. Feed production: According to Benavides et al. (2020), swine feed has about 0.4 kg CO_2,e/kg feed. If we have a feed conversion ratio of 2.5 lb feed/lb live weight gain, then 1 kg CO_2,e/kg of pig sold. Assuming 2.2 turns a year and 280 lb pigs sold, this results in 265 kg CO_2,e/head-year.
6. Feed movement: The average freight truck in the U.S. emits 162 grams of CO₂ per ton-mile. Every pig space needed 0.73 tons of feed/year, and assuming feed was delivered 100 miles gives 12 kg CO_2,e/head-year.
7. Pig movement: Again, assuming 100 miles of pig transport to the processing plant (finish weight of 280 lb) and 100 miles from the nursery facility (15 lb wean pig) gives 5.2 kg CO_2,e/head-year.

 

I had a carbon footprint of 0.5 tons CO_2,e/pig space per year, or about 2 kg CO_2,e/kg live weight produced or 3 CO_2,e/kg of "take home" meat. Two caveats, I didn't include the carbon footprint associated with generating piglets or dealing with mortalities. We can do something easy for mortalities, like assume a 3% death loss and multiply our results by 3%. Assuming culled animals used all the feed and generated all the manure they would have if they were alive, gives a cushion for using energy to handle the carcasses. The approach raises the lifecycle costs to 0.51 tons CO_2,e/pig space per year, and 3.2 CO_2,e/kg of "take home" meat. Unfortunately, I don't have a simple trick to deal with generating piglets. To get this estimate, we need to work on an example sow farm (there is always next time).

 

Figure 1. Percent of swine finishing greenhouse gas emissions from different sources.

 

It's important to note that achieving carbon neutrality in livestock production will require a combination of these strategies, and the feasibility of implementation can vary depending on factors such as location, scale of production, available resources, and livestock species. Regular assessment, adaptation, and improvement are necessary to ensure ongoing progress toward carbon neutrality.