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Greenhouse Gas Emissions from Pig and Chicken Supply Chains

11 October 2013

This new report from the United Nations Food and Agriculture Organization (FAO) presents the results from an assessment carried out to improve the understanding of greenhouse gas (GHG) emissions along livestock supply chains for pigs, poultry meat and eggs.

Background and Purpose

The livestock sector is one of the fastest growing sub-sectors of the agricultural economy, and faces several unprecedented and concomitant challenges, according to the FAO report, Greenhouse Gas Emissions from Pig and Chicken Supply Chain. The sector needs to respond to the increasing demands for livestock products that are arising from population growth and changing consumer preferences. It also has to adapt to changes in the economic and policy contexts, and in the natural environment upon which production depends. At the same time, it has to improve its environmental performance and mitigate its impact on climate.

The pig sector is the biggest contributor to global meat production, with 37 per cent in 2010. Chicken meat accounts for about 24 per cent. Global demand for pig meat, chicken meat and chicken eggs are forecast to grow by 32 per cent, 61 per cent and 39 per cent respectively during the period 2005-2030. If the greenhouse gases (GHG) emissions intensities (emission intensity; or the kg of GHG per kg of product) of these commodities are not reduced, the increases in production required to meet demand will lead to proportionate increases in GHG emissions.

Improving our understanding of where and why emissions arise in livestock supply chains is an important step towards identifying ways to improve efficiency and reduce emissions intensity. This report presents a life cycle assessment (LCA) of the GHG emissions arising from pig and chicken supply chains. It provides a detailed analysis of emissions according to region, sector and systems of production. In addition to informing efforts to reduce GHG emissions, it is hoped that the assessment will also help inform public debate on this important subject.


Authors of the FAO report explain that their analysis is based on a LCA approach and includes:

  • pre-farm emissions arising from the manufacture of inputs
  • on-farm emissions during crop and animal production; and
  • post-farm emissions arising from the processing and transportation of products to the retail point.

Emissions and food losses that arise after delivery to the retail point are not included.

While gases of minor importance have been omitted, the three major GHG in agriculture are included, namely: methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2).

The Global Livestock Environmental Assessment Model (GLEAM) was developed to carry out this assessment. This model quantifies GHG emissions arising from production of the main livestock commodities: meat and milk from cattle, sheep, goats and buffalo; meat from pigs; and meat and eggs from chickens. The model calculates total emissions and (commodity) production for a given farming system within a defined area. The emissions per unit of product can be calculated for combinations of different commodities/farming systems/locations at different spatial scales. Emissions are calculated around the year 2005, the most recent year for which all input data and parameters are available. In a complex analysis such as this, results are not definitive, but rather the best assessment that could be made and subject to improvement in subsequent revisions.

Methodological developments are being developed within the context of the LEAP Partnership (Livestock Environmental Assessment and Performance), to harmonise metrics and approaches used in the assessment of environmental performance of livestock supply chains, including future updates of this report.

Key Findings

Globally, GHG emissions from pig and chicken supply chains are relatively low, according to FAO.

Pig supply chains are estimated to produce 0.7 gigatonnes of carbon dioxide-equivalent per annum,  representing nine per cent of the livestock sector’s emissions.

Chickens are estimated to emit 0.6 gigatonnes of carbon dioxide-equivalent, representing eight per cent of the livestock sector’s emissions.

While their emissions are comparatively low, the sector's scale and rate of growth require reductions in emission intensity.

Main Emissions Sources

Pig supply chains

Feed production contributes 60 per cent of the emissions arising from global pig supply chains, and manure storage/processing, 27 per cent, according to FAO. The remaining 13 per cent arises from a combination of post-farm processing and transport of meat (six per cent), direct and indirect energy use in livestock production (three per cent) and enteric fermentation (three per cent).

Of the feed emissions, nitrous oxide resulting from the application of synthetic and organic fertilisers in feed crop production accounts for 17 per cent of total pig emissions, while carbon dioxide from the use of energy in field operations, crop transport and processing, and the manufacture of fertiliser and synthetic feed materials accounts for 27 per cent.

An additional 13 per cent of the total emissions arises from land-use change (LUC) driven by increased demand for feed crops. The remaining feed emissions (three per cent) are methane from flooded rice cultivation. Total direct and indirect energy consumption across the supply chain accounts for 37 per cent of the total emissions.

Chicken meat and egg supply chains

For chicken meat, FAO says that feed production contributes 78 per cent of emissions, direct on-farm energy use eight per cent, post-farm processing and transport of meat, seven per cent and manure storage/processing, six per cent.

For eggs, feed production contributes 69 per cent of emissions, direct on-farm energy use four per cent, post-farm processing and transport of meat, six per cent and manure storage and processing, 20 per cent.

Meat has higher feed emissions than eggs, partly because rations for broiler chickens, on average, include a higher share of soybean and therefore more soybean sourced from areas where LUC is taking place. Consequently, LUC accounts for 21 per cent of meat emissions and 13 per cent of egg emissions.

Eggs have higher manure emissions because layers have a greater proportion of their manure managed in anaerobic conditions, which lead to higher methane emissions. Feed emissions arising from fertiliser application and energy use are important for both meat and eggs: nitrous oxide from fertiliser application accounts for 32 per cent of meat and 30 per cent of egg emissions, while carbon dioxide arising from energy use in feed production accounts for 25 per cent and 27 per cent for meat and eggs respectively.

Total direct and indirect energy consumption across the supply chain accounts for 41 per cent of the total emissions for meat and 37 per cent for eggs.

Summary of the Factors Influencing Emission Intensity

Emission intensities can be influenced by a combination of factors, depending on the species, system and region in question, according to the FAO report.

Some of the key factors are summarised briefly below.

Feed conversion ratio (FCR)

As feed production is the activity that produces the most GHG for both monogastric species, the efficiency with which pigs and chickens convert feed into edible products is a key determinant of emission intensity. Due primarily to physiological differences, the individual broiler or laying hen tends to be a more efficient converter of feed into edible products than the growing pig. Furthermore, backyard pigs and chickens have higher FCRs than their commercial equivalents, due to differences in the breeds used, feed quality and availability, and management strategies.

Land-use change

Land-use change arising from increased demand for feed crops is a major driver of emissions but its quantification is associated with strong methodological and data uncertainty. Pigs and chickens that have a higher proportion of their ration consisting of soybean produced in countries where LUC is occurring will tend to have significantly higher feed emissions.

Manure management

Manure emissions are a function of the rate at which volatile solids or nitrogen are excreted, and the rate at which they are subsequently converted to methane or nitrous oxide during manure management. High FCRs and low digestibility of feed tend to produce higher rates of volatile solids and nitrogen excretion, and explain, for example, why backyard chickens have higher manure nitrous oxide emissions.

The rate at which volatile solids are converted to methane depends on the way in which the manure is managed and the ambient temperature. Higher temperatures combined with anaerobic conditions in manure management tend to lead to high conversion rates of volatile solids to methane.

Energy use

When summed across the supply chains, emissions from energy use account for 37 per cent of the total emissions arising from production of eggs and pig meat and 41 per cent of the emissions from chicken meat.

The emission intensity of energy production depends on the types of fuels used and the efficiency of energy conversion and distribution.

Furthermore, as most of the energy emissions arise as a result of feed production, FCR is also a key determinant of the energy emission intensity per kg of eggs or meat.

Herd/flock structure

The size of the breeding overhead is small in commercial pig and chicken systems, and therefore variation in the herd/flock structure has a limited impact on the overall emissions intensity in these systems. However in backyard systems, where death rates are high and fertility rates low, breeding animals make up a greater proportion of herd/flock and therefore variation in the size of the breeding overhead can be a significant influence on emissions intensity.

Variation in Emissions Intensity between Production Systems

Pig supply chains

The FAO report concludes that industrial systems, which account for 60 per cent of global production, have lower emission intensities than intermediate systems due to a combination of lower feed conversion ratios, more digestible rations and lower shares of rice products in the ration.

The emission intensity of backyard pigs is lower than the other systems primarily because the emissions per kg of feed are significantly lower for backyard pigs (although the low feed emissions are partially offset by their higher FCRs). The higher FCRs lead to higher rates of excretion of both volatile solids and nitrogen per kg of meat produced, which result in higher manure emissions. In addition, backyard pigs are assumed to have negligible emissions arising from LUC or from post-farm processing and transport of meat.

Chicken supply chains

On average, layers have a lower emission intensity than broilers or backyard systems, when measured in terms of emissions per kg of protein, reports FAO. Although layers have higher manure methane emissions than broilers, this is compensated by their lower emissions per kg of feed (as a result of having less soybean in their ration and, consequently, lower LUC emissions) and their lower FCR.

Backyard systems have significantly higher FCRs than layers or broilers due to the lower physical performance. This is exacerbated by the structure of the backyard flocks, which have higher proportions of relatively unproductive breeding animals due to higher death rates and lower fertility rates. The amount of nitrogen excreted per kg of protein produced is therefore higher in backyard systems, which leads to higher manure nitrous oxide emissions.

Regional Variation in Emission Intensity

Emission intensities vary between the main producing regions, the FAO found. Differences are mostly explained by variation in feed materials in the ration, animal productivity and manure management.

Pig supply chains

There is significant regional variation in average FCR in backyard systems, which leads to variations in the feed emissions. For example, the FCR of backyard pigs in Sub-Saharan Africa is 35 per cent greater than that of Eastern Europe, when measured at the herd level. The variations in FCR arise due to differences in parameters such as genetic potential, nutrition and health status. The regional differences in FCR are less marked in intermediate and industrial systems, reflecting the greater levels of standardisation.

For industrial pigs, the emissions per kg of feed can vary a great deal between regions, depending on the amount of soybean in the ration, and the proportion of the soybean that is sourced from countries where LUC is occurring. This leads to markedly higher feed emissions for industrial pigs in Latin America and Western Europe. In intermediate systems, the presence of rice feed products leads to significant increases in feed emissions in Asia.

Regions that have higher than average manure methane emissions include: backyard pigs in South Asia (due to high temperatures and high volatile solids excretion rates); intermediate pigs in East and South east Asia (due to high temperatures and liquid manure management); and industrial pigs in North America (due to the use of lagoons/slurry/pits with long storage, and the higher biodegradability of the manure).

Chicken supply chains

There is significant regional variation in average FCR in backyard systems, which leads to variations in the feed emissions. For example, the FCRs of backyard chickens in Sub-Saharan Africa and East and South east Asia are more than twice those in Eastern Europe, when measured at the flock level. As with backyard pigs, the variations in FCR arise due to differences in parameters such as genetic potential, nutrition and health status – with backyard chickens particularly susceptible to disease and predation. In contrast, the regional differences in FCR are negligible for broilers and layers, reflecting the high degree of standardization in these systems.

For broilers and layers, the emissions per kg of feed can vary a great deal depending on the amount of soybean sourced from areas associated with LUC. As with industrial pigs, this leads to higher emissions in regions such as Latin America and Western Europe. In backyard systems, the carbon dioxide emissions arising from energy use in field operations are lower in regions such as Sub-Saharan Africa and Asia, where a significant proportion of the work is undertaken using animal draft power.

Finally, feed nitrous oxide varies between regions in response to differences in the rates at which nutrients are applied to, and used by, crops. Manure nitrous oxide emissions in backyard systems are higher in Sub-Saharan Africa and Asia, due to the higher FCRs in these regions. For layers, manure methane emissions tend to be lower in regions where solid storage (i.e. North America and South Asia) or drylots (Eastern Europe) predominate.


The range of emission intensity, both across and within supply chains, suggests that there is room for improvement, concludes FAO.

The following areas show particular promise for reducing emissions:

  • reducing land use change (LUC) arising from feed crop cultivation
  • improving the efficiency of crop production, particularly improving fertilization management
  • improving the efficiency of energy generation and supply, and of energy use, both on-farm (in housing and field operations) and off-farm (manufacture of agricultural inputs, and transportation and processing of farm products)
  • reducing use of uncovered liquid manure management systems (MMS), particularly in warm climates
  • improving feed conversion of the individual animal (through, for example, better breeding techniques) and also of the herd (by reducing losses to disease and predation, particularly in backyard systems);
  • providing balanced animal nutrition.

Finally, FAO adds that it should be borne in mind that this report focuses on a single measure of environmental performance, i.e. kg carbon dioxide-equivalents per kg commodity. When evaluating GHG mitigation measures, attention should be paid to the potential impacts on other policy objectives, such as sustaining water resources, improving food security and reducing poverty.


MacLeod, M., Gerber, P., Mottet, A., Tempio, G., Falcucci, A., Opio, C., Vellinga, T., Henderson, B. and Steinfeld, H. 2013. Greenhouse gas emissions from pig and chicken supply chains – A global life cycle assessment. Food and Agriculture Organization of the United Nations (FAO), Rome.

Further Reading

You can view the full report by clicking here.

October 2013

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