7.1 Livestock
| Category ID | Description | EIC |
|---|---|---|
| 2333 | Enteric Fermentation - Dairy Cows | 62061802620101 |
| 2334 | Enteric Fermentation - Range Cattle | 62061802620102 |
| 2335 | Enteric Fermentation - Sheep | 62061802620108 |
| 2336 | Enteric Fermentation - Goats | 62061802620110 |
| 2337 | Enteric Fermentation - Horses | 62061802620109 |
| 2338 | Manure Management - Dairy Cows | 62061802620101 |
| 2339 | Manure Management - Range Cattle | 62061802620102 |
| 2340 | Manure Management - Sheep | 62061802620108 |
| 2341 | Manure Management - Goats | 62061802620110 |
| 2342 | Manure Management - Horses | 62061802620109 |
| 2343 | Manure Management - Swine | 62061802620107 |
| 2344 | Manure Management - Broilers | 62061802620104 |
| 2345 | Manure Management - Turkeys | 62061802620106 |
| 2346 | Manure Management - Layers & Pullets | 62061802620105 |
Introduction
This methodology outlines the approach for estimating greenhouse gas (GHG) emissions from the animal livestock subsector. Livestock generally refers to animals like cattle, pigs, sheep, goats, and poultry that are raised to produce food for humans, such as meat, milk, and eggs, but also includes recreational and working animals such as horses. The primary sources of these emissions are two key processes: enteric fermentation and manure management. These processes, described in detail below, are significant contributors to national-scale methane (CH₄) and nitrous oxide (N₂O) emissions (USEPA, 2024), both of which are potent GHGs with a much higher global warming potential (GWP) than carbon dioxide (CO2). In the San Francisco Bay Area (SFBA), the animal livestock population is divided into several subgroups to accurately estimate emissions. These subgroups include dairy cattle, which are raised for milk production; range cattle, primarily raised for beef/meat consumption; poultry, which is further divided into layers and pullets (for egg production) and broilers (for meat production); as well as swine, sheep, horses, and goats.
Enteric Fermentation
Enteric fermentation is a natural digestive process that occurs in the stomachs of ruminant (defined as animals with four-chamber stomachs that chew their cud and regurgitate it) animals, such as cattle, sheep, and goats, and, to a lesser extent, in some non-ruminants like horses. Microorganisms in the digestive tract of certain animals break down complex organic matter, such as cellulose, producing CH₄ as a byproduct. CH₄ is released primarily through belching. The amount of CH₄ produced depends on several factors, including the type of animal, feed composition, and feeding practices. Enteric fermentation is a significant contributor to global agricultural GHG emissions, especially in regions with large populations of ruminant animals.
Manure Management
Manure management encompasses the collection, storage, treatment, and disposal of livestock waste. CH₄ emissions occur when manure is stored or treated under anaerobic conditions, such as in lagoons, pits, or other liquid-based systems. N₂O emissions are generated when manure decomposes aerobically with oxygen or during processes such as nitrification and denitrification in manure-handling systems. The type of manure management system, climatic conditions, and the species of livestock involved influence the quantity and type of GHG emissions. Properly managing manure is critical for reducing its environmental impact and minimizing emissions. Anaerobic digestion processes where biogas from animal waste is captured and used for heating or energy production is reported in fuel combustion categories.
Methodology
This section describes how GHG emissions are estimated for animal livestock source categories. Livestock categories are considered area source categories as they account for emissions from sources that are not directly permitted by the Bay Area Air Quality Management District (Air District), and thus not routinely or annually catalogued. The methodology used to calculate emissions for the reported base year(s) of livestock area sources is as follows:
Base Year(s) Emissions county,pollutant =
Activity Data × Emission Factorpollutant × Control Factorpollutant × Fractioncounty × Fractionin District
× GWP pollutant
Where:
- Base Years: are years for which activity/throughput data are available in order to calculate emissions.
- Activity Data: is the total regional throughput or activity data for applicable reported base years.
- Emission Factorpollutant: is a factor that allocates an amount of emissions, in mass, of a particular pollutant by unit of activity data.
- Control Factorpollutant : is a fractional ratio (between 0 and 1) that captures the estimated reduction in emissions as a result of Air District rules and regulations.
- Fractioncounty : is the fraction of total regional emissions (between 0 and 1) estimated to be allocated to a particular county.
- Fractionin District: The Air District jurisdiction covers only a portion of Solano and Sonoma County and, therefore, an additional allocation is applied to these counties that proportions each county’s emissions that are within Air District’s boundary.
- GWPpollutant is the Global Warming Potential of a particular GHG pollutant. The current version of the GHG emissions inventory incorporates the global warming potential (GWP) reported in the Fifth Assessment report of the Intergovernmental Panel for Climate Change (IPCC, 2014). The GWPs for the three principal GHGs are 1 for carbon dioxide (CO2), 34 for methane (CH4), and 298 for nitrous oxide (N2O), when calculated on a 100-year basis with climate-carbon feedback included.
Once base year emissions are determined, historical backcasting and forecasting of emissions relative to the base year’s emissions are conducted using growth profiles as follows:
Current Year Emissions county = Base Year(s) Emission county × Growth Factor
Where:
- Growth Factor: is a scaling factor that is used to derive historical emissions estimates for years for which activity data and/or emissions are not available, and to forecast emissions for future years, using surrogates that are assumed to be representative of activity and/or emissions trends
More details on activity data/throughput, county distribution, emission factors and controls are provided in the following subsections.
Activity Data / Throughput
Activity data for livestock processes is queried from the US Department of Agriculture (USDA) National Agricultural Statistics Service (NASS) Quick Stats database, which is an online tool that includes statistics on crops, livestock, agricultural practices, and economic data (USDA, 2024). The database offers detailed activity data at state, county, and national levels. Data is collected by surveys conducted by the USDA Census of Agriculture division every five years and includes statistics for a wide range of livestock categories, including dairy cows, range cattle, sheep, goats, poultry (broilers, turkeys, layers), horses, and swine. The most recent survey years are 2017 and 2022. The 2022 population data for each livestock category is used as the base year activity estimate for each county and it is assumed that the livestock populations remained constant from 2022 to 2023. The fraction used to proportion the county level cattle population into dairy cows versus range cattle is derived from the year 2015 CARB GHG inventory and held constant for all years since then (CARB, 2023).
County Distribution / Fractions
County fractions are derived from the 2022 county-level animal livestock population data from the USDA NASS Quick Stats database. Since data is updated infrequently (every five years), the county distribution is assumed to remain constant until the next update of the NASS database. The table below shows the county distribution for livestock categories for base year 2022.
| ID | Description | ALA | CC | MAR | NAP | SM | SNC | SOL | SON |
|---|---|---|---|---|---|---|---|---|---|
| 2333 | Enteric Fermentation - Dairy Cows | 0.05 | 0.21 | 0.28 | 0.10 | 0.00 | 0.00 | 0.00 | 0.35 |
| 2334 | Enteric Fermentation - Range Cattle | 0.11 | 0.22 | 0.12 | 0.08 | 0.03 | 0.12 | 0.27 | 0.06 |
| 2335 | Enteric Fermentation - Sheep | 0.01 | 0.03 | 0.05 | 0.01 | 0.01 | 0.01 | 0.78 | 0.09 |
| 2336 | Enteric Fermentation - Goats | 0.06 | 0.00 | 0.00 | 0.17 | 0.12 | 0.12 | 0.36 | 0.16 |
| 2337 | Enteric Fermentation - Horses | 0.10 | 0.15 | 0.09 | 0.08 | 0.20 | 0.19 | 0.04 | 0.14 |
| 2338 | Manure Management - Dairy Cows | 0.05 | 0.21 | 0.28 | 0.10 | 0.00 | 0.00 | 0.00 | 0.35 |
| 2339 | Manure Management - Range Cattle | 0.11 | 0.22 | 0.12 | 0.08 | 0.03 | 0.12 | 0.27 | 0.06 |
| 2340 | Manure Management - Sheep | 0.01 | 0.03 | 0.05 | 0.01 | 0.01 | 0.01 | 0.78 | 0.09 |
| 2341 | Manure Management - Goats | 0.06 | 0.00 | 0.00 | 0.17 | 0.12 | 0.12 | 0.36 | 0.16 |
| 2342 | Manure Management - Horses | 0.10 | 0.15 | 0.09 | 0.08 | 0.20 | 0.19 | 0.04 | 0.14 |
| 2343 | Manure Management - Swine | 0.02 | 0.03 | 0.28 | 0.02 | 0.00 | 0.13 | 0.09 | 0.44 |
| 2344 | Manure Management - Broilers | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.99 |
| 2345 | Manure Management - Turkeys | 0.00 | 0.33 | 0.30 | 0.06 | 0.00 | 0.00 | 0.00 | 0.32 |
| 2346 | Manure Management - Layers & Pullets | 0.00 | 0.01 | 0.08 | 0.01 | 0.01 | 0.01 | 0.02 | 0.87 |
BAAQMD Jurisdiction Fraction
The Air District’s jurisdiction covers only portions of Solano and Sonoma counties, with the remaining areas managed by other Air Districts. Estimates for the dairy, range, and feedlot cattle populations that fall within the Air District’s jurisdiction are based on the California Air Resources Board’s (CARB) methodology on estimating emissions from the Animal Husbandry subsector (CARB, 2004) for the year 2000, that utilizes locations of animal populations from California Department of Food and Agriculture (CDFA, 2001). The proportions for Solano and Sonoma counties are detailed below:
County | % of Livestock Dairy and Cattle within the Air District’s jurisdiction |
Solano | 48% |
Sonoma | 39% |
Emission Factors
CH4 and N2O emission factors for livestock processes are obtained and/or derived from the CARB greenhouse gas inventory (CARB, 2023).
Enteric Fermentation
For enteric fermentation categories, CH4 emission factors are reported by animal category in the CARB GHG inventory. Emissions factors for sheep, goats, horses and swine are directly available. Emission factors for the cattle source categories (dairy cattle and range cattle) reported in this inventory are calculated by deriving a composite emissions factor by dividing the sum of total statewide emissions for each subgroup (e.g. dairy calves, heifers, steer etc.) by the sum of respective livestock population for each animal category. For example, a composite emission factor for dairy cattle is the sum of emissions from dairy cows, dairy calves, and dairy replacements divided by the total dairy cattle population.
Manure Management
For manure management categories, N2O emission factors are calculated using the same method as enteric fermentation, where the sum of total statewide emissions for each manure management subgroup (e.g., dry lot and pasture practices for goats; anaerobic digester, daily spread, deep pit, liquid/slurry, pasture and solid storage practices for dairy cows, etc.) is divided by the total livestock population for each manure management practice. The manure management practices by animal-type are presented in more detail in the Appendix at the end of this methodology documentation.
As methane is produced at different rates depending on the manure management practice and emissions are dependent on the throughput of manure management process (data not available) rather than animal counts (data is available), it is difficult to quantify the emissions from each individual manure management process. Therefore, a composite CH4 emission factor approach for manure management subsector is adopted.
This approach estimates the CH4 emission factor for manure management of any given animal sub-group by multiplying the ratio of total statewide enteric fermentation CH4 emissions (from the CARB GHG inventory) to total statewide manure management CH4 emissions for that animal sub-group, by the derived composite enteric fermentation CH4 emission factor for that particular animal subgroup. This calculation approach assumes that CH4 emissions from enteric fermentation and manure management are proportional to and dependent on each other, and their relative proportion remains constant since activity data in each sub-group is the same for both emissions processes (animal count). This eliminates the need for deriving composite emissions factors for each manure management practice sub-type (a computational requirement for N2O).
Control Factors / Emission Controls
The District adopted Regulation 2-10: Large Confined Animal Facilities in 2006 (BAAQMD, 2006) requiring control measures to reduce nitrogen oxides, particulate matter, and organic compounds from permitted facilities that maintain a minimum number of animals for commercial agricultural purposes. Currently, no facilities are meeting the minimal animal counts required to be subject to the regulation. Since there are no current livestock processing facilities subject to Air District rules, no control factors are formally applied in the emissions calculations.
However, CARB enacted Senate Bill 1383 in 2016, which mandates a 40% reduction in methane emissions from the dairy and livestock sector below 2013 (SB1383) levels by 2030 (SB1383, 2016). This legislation targets future emissions from both enteric fermentation and manure management that are incorporated in the projections . Under SB 1383, facilities have flexibility to choose from a range of approved, feasible strategies to achieve the projected reduction in CH4 emissions from manure management processes include adoption of anaerobic digesters to collect and utilize the CH4 produced for heat and power, and alternative manure management practices like daily spread, composting etc. Enteric methane-reducing technologies and controls are also being researched and implemented such as feed additives and dietary improvements in livestock to reduce CH4 emissions.
Historical Emissions
For the years 2012 to 2021, historical activity and emissions are estimated using data from the USDA NASS Quick Stats database. Since USDA survey data is collected every five years (2012, 2017, and 2022), activity data for the intervening years (without survey data) are linearly interpolated.
Agricultural and natural resources sector employment data from the Association of Bay Area Governments (ABAG, 2024) is used as the backcast profile for livestock categories for years 1990-2011. The backcast profile assumes that the GHG emissions from livestock activity follow employment trends in the agricultural sector.
Future Projections
Growth profiles for livestock categories are obtained from CARB’s 2022 Scoping Plan for Achieving Carbon Neutrality, which lays out a path to achieve targets for carbon neutrality and reduce anthropogenic GHG emissions by 85 percent below 1990 levels no later than 2045 (CARB, 2022). The 2022 Scoping Plan relies on the PATHWAYS scenario model, which simulates GHG emissions reductions across sectors (CARB, 2021). The model accounts for the impacts of different policy measures, adopted regulations including the mandated reductions based on SB 1383, technological adoption rates, and economic trends. The 2022 Scoping Plan provides specific projections for enteric fermentation and manure management emissions (“Agriculture – Enteric & Manure”), which are used to forecast future year emissions for years 2023-2050. . The future year projections incorporate SB 1383 mandates, which require a 40% reduction in methane emissions from livestock processes relative to 2013 levels by 2030.
Sample Calculations
The table below shows an example for calculating base year 2022 GHG emissions in units of metric tons per CO2 equivalents (MTCO2eq/year) from manure management from dairy cows (Category # 2338) in the SFBA portion of Sonoma County.
Step 1 | Obtain all cattle population in Sonoma County in 2022 (USDA, 2024) | 52,370 heads | |
Step 2 | Obtain percent of livestock cattle in Sonoma County (CDFA, 2001; CARB, 2004) | 39.3% | |
Step 3 | Estimate the total cattle population in Sonoma County | 52,370 × 0.393 = 20,581 | |
Step 4 | Obtain Fraction of Sonoma county dairy cow population that is within the Air District jurisdiction (CDFA, 2001) | 75.04% | |
Step 5 | Estimate the dairy cow population in Sonoma County that is within the SFBA | 20,581 × 0.7504 = 15,444 | |
CH4 | N2O | ||
Step 6 | Composite emission factors for manure management dairy cow sub-group (CARB, 2023) (lbs/head) | 261.37 | 0.9607 |
Step 7 | Calculate emissions from manure management using the emissions factors and dairy cow population (lbs/year) | 261.37 × 15,444 = 4,306,674 | 0.9607 × 15,444 = 14,837 |
Step 8 | Global Warming Potential | 34 | 298 |
Step 9 | Calculate emissions using GWP (MTCO2eq/year) | 4,306,674 × 34 = 137,246,919 lb/yr | 14,837 × 298 = 4,421,524 lb/yr |
(137,246,9194 + 4,421,524) lb/year × 1/2000 ton/lb × 0.907 MT/ton = 64,247 MTCO2eq/year | |||
Assessment of Methodology
The general methodology for determining emissions for these categories has not changed although most of the data inputs have been updated including use of the latest livestock population from USDA and forecasting emissions based on SB1383.
Emissions
The table below shows the total GHG emissions by pollutant in (MTCO2eq) for livestock categories.
| ID | Description | CH4 | N2O | Total |
|---|---|---|---|---|
| 2338 | Manure Management - Dairy Cows | 212466.2 | 6844.9 | 219311.1 |
| 2334 | Enteric Fermentation - Range Cattle | 181302.9 | 0.0 | 181302.9 |
| 2333 | Enteric Fermentation - Dairy Cows | 164240.0 | 0.0 | 164240.0 |
| 2335 | Enteric Fermentation - Sheep | 13534.6 | 0.0 | 13534.6 |
| 2339 | Manure Management - Range Cattle | 8338.0 | 2600.7 | 10938.7 |
| 2346 | Manure Management - Layers & Pullets | 4856.7 | 418.9 | 5275.6 |
| 2337 | Enteric Fermentation - Horses | 5001.2 | 0.0 | 5001.2 |
| 2342 | Manure Management - Horses | 912.7 | 2173.2 | 3085.9 |
| 2340 | Manure Management - Sheep | 1192.9 | 1057.7 | 2250.6 |
| 2344 | Manure Management - Broilers | 658.5 | 498.0 | 1156.5 |
| 2336 | Enteric Fermentation - Goats | 975.8 | 0.0 | 975.8 |
| 2343 | Manure Management - Swine | 526.4 | 29.3 | 555.7 |
| 2341 | Manure Management - Goats | 73.3 | 53.2 | 126.5 |
| 2345 | Manure Management - Turkeys | 3.4 | 5.7 | 9.1 |
Summary of Base Year 2022 Emissions
Animal livestock produces CH4 and N2O emissions which are accounted for in this inventory through enteric fermentation and manure management source categories, by animal subgroup. The majority (roughly 95%) of the GHG emissions from livestock processes come from cattle, including dairy cows and range cattle. Methane generated from the digestive process of range cattle (category 2334) contributes the most methane in this subsector followed by manure management (category 2338) from dairy cows.
The tables below show the contribution of animal livestock GHG emissions to the overall regional total and to the Agriculture sector total. Animal livestock is a major source of CH4 emissions, contributing 14% to the SFBA regional inventory of CH4. Although manure management from animal livestock produces N2O emissions, their overall contribution is a little above 1% to the regional N2O emissions inventory.
Contribution of Livestock Emissions by Sector| Subsector | Sector | Subsector GHG Emissions (MMTCO2eq) | Sector GHG Emissions (MMTCO2eq) | % of Sector |
|---|---|---|---|---|
| Livestock | Agriculture | 0.61 | 1.26 | 48.16% |
Contribution of Livestock Emissions to Regional Total
| Subsector | Subsector GHG Emissions (MMTCO2eq) | Regional Total GHG Emissions (MMTCO2eq) | % of Regional Total |
|---|---|---|---|
| Livestock | 0.61 | 65.68 | 0.93% |
Trends
The time series chart below shows the emission trends for livestock categories.
Summary of Trends
GHG emissions from animal livestock sources have decreased over time since 2005 and are projected to continue decreasing until 2030 to achieve the requirements of SB 1383, after which emissions are projected to remain constant. The combined GHG emissions from cattle livestock in 2030 (0.41 MMTCO2eq) are projected to be approximately 40% lower than the combined GHG emissions from cattle livestock in 2013 (0.68 MMTCO2eq), consistent with the mandated reductions outlined in SB 1383.
The recent decrease in GHG emissions from livestock processes (2011-2021) are attributed to a decrease in the number of dairy cows and range cattle raised in the SFBA. This is due to a combination of factors, including relocation of dairy farms to more cost-effective regions such as the Central Valley, consolidation of smaller dairy farms into larger dairy farms outside of SFBA, and conversion of farmland into more economically viable and less water intensive processes such as vineyards and organic crop farming.
Uncertainties
The USDA NASS Quick Stats database reports livestock populations only for those counties that meet a minimum threshold of livestock farms to protect the confidentiality of individual operations. As the data represents a snapshot of farm practices and animal populations, the data has the following uncertainties:
- Independent smaller farms animal populations are not included in the NASS database so the total number of animals for each county may be under reported.
- Seasonal changes in farm operations are not captured in the assessment.
- Fluctuations in the farm population from illness, deaths, and sell offs throughput the year are not characterized.
- Farms may consolidate, change ownership, or open new ones in between reporting years and therefore, the emissions may be higher or lower than what is reported.
Since data is reported by farms to USDA every five years, interpolation is used to estimate activity data and emissions for years where no survey is conducted. Actual activity and emissions for these years may differ from the linearly interpolated values. The county distribution is also assumed to be constant in each five-year span, even though actual county fractions likely vary from year to year due to changing livestock populations for each farm.
The livestock population fraction for Solano and Sonoma counties within the Air District’s jurisdiction is based on the year 2000 cattle and calves inventory summary from the California Department of Food and Agriculture (CDFA, 2001). The present-day livestock population split in these counties for the year 2022 may differ significantly due to changes in agricultural practices or demographic shifts in the livestock population since 2000. To enhance accuracy, future inventories will utilize county zoning maps and data from various SFBA County Crop Reports, which will help refine and update the estimate of the livestock population fraction within the Air District’s jurisdiction.
The composite emission factor for methane from manure management was estimated assuming that enteric fermentation emissions are proportional to the manure management emissions; however, this approach does not account for variations in emission rates across different manure management processes, which may potentially lead to minor over- or under-estimation.
Contact
Author: Michael Nguyen
Reviewer: Abhinav Guha
Last Update: 8/20/2025
References
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