Greenhouse gas intensity of average sheep systems in Ireland

Jonathan Herron, Teagasc, recently discussed greenhouse gas intensity of sheep systems in Ireland at the Teagasc National Sheep Conference.

The Food and Agriculture Organisation has projected that the global demand for agricultural products will increase by 12% over the next decade (2021-2030) as a result of population growth. While large ruminants (e.g. cows) get more focus, small ruminants (i.e. sheep and goats) are key players in the global agricultural economy due to their ability to adapt to a wide range of climates and environments. Although sheep meat is a small contributor to total global meat consumption, global production is expected to increase by 2 million tonnes (12.7%) between 2021 and 2030 to meet growing demand.

Figure 1. National agricultural greenhouse gas emissions 1990-2020

Figure 2. Total greenhouse gas emissions (kt CO2 equivalent) from sheep and total breeding ewe
population 1990-2020.

In Ireland, the sheep sector is important as it generates approximately €300 million per annum. Within the European Union, Ireland is the largest net exporter of sheep meat, with the domestic market accounting for less than 7%. However, as with all food production systems, sheep systems can have negative environmental effects, the most pressing in the current climate being greenhouse gas (GHG) emissions, for which the EU and Ireland have set ambitious reduction targets. Consumers are also becoming increasingly concerned and conscious of how the food they consume is produced, particularly livestock products where purchasing decisions are increasingly influenced by environmental concerns, animal welfare, and human health. To reduce the negative environmental impact of livestock production systems, while meeting global demand and consumer expectations, the sheep sector is required to identify and adopt practices that are environmentally sustainable, economically viable, and socially acceptable.

National greenhouse gas emissions from the sheep sector

Every year the Environmental Protection Agency publishes the national GHG inventory report which outlines the quantity and sources of GHG emissions across all sectors within Ireland for a given and previous years. In the most recently reported year, 2020, Ireland emitted 58,766 kilotonnes (kt) CO2 equivalent of which 38% came from the agricultural sector. The digestion of feed and the release of methane (i.e. enteric fermentation) dominates agricultural emissions, contributing 61.4%. The remaining GHG emissions are predominantly associated with manure and synthetic fertiliser application (Figure 1). Sheep directly emitted 1,065 kt CO2 equivalent through the digestion of feed and manure management. However, the sheep sector is also indirectly responsible for GHG emissions from the use of synthetic fertilisers, fuel and electricity, which are recorded separately. The current method of calculating national sheep GHG emissions is based on a fixed emission value per head for each breed type (i.e. lowland vs. hill) and animal type (e.g. breeding ewe vs. lamb). This is evident in Figure 2 where total GHG emissions from the sheep sector follows a near identical trend to breeding ewe numbers.

In an attempt to avoid the negative impacts of climate change, the European Union has committed to reduce GHG emissions to at least 55% below 1990 levels by 2030. To achieve this target the Irish agricultural sector has been given a 2030 GHG reduction target of 25% compared to 2018 levels. Work is currently underway to develop a new method for calculating GHG emissions from the sheep sector. This method will ensure any improvements in the efficiency of a production system and adoption of technologies will translate in the national GHG inventory and thus contribute to the national GHG reduction targets. For the agricultural sector to achieve the 2030 GHG reduction target, adoption of recommended practices and the identification of new technologies will be required at farm level.

Life cycle assessment modelling

Life cycle assessment (LCA) is an internationally recognized methodology used to calculate the environmental impact of all life stages of a product, process, system or service. Teagasc has developed LCA models to calculate the environmental impact of agricultural systems in Ireland. The Teagasc Sheep LCA model adopts a cradle to farm gate boundary, meaning all GHG emissions up to the point at which the product (live weight and wool) leaves the farm are accounted for. Not only are on-farm emissions accounted, but also emissions released during the production of farm inputs (i.e. fertilisers, electricity, concentrate feed). By applying this boundary, LCA can identify the key emission sources and identify management practices that have potential to reduce GHG emissions. To determine the GHG reduction potential of proposed management practices and emerging technologies, and how they may contribute to meeting the agricultural sector’s 25% GHG reduction target, it is vital to first determine the performance of an average production system. This sets a baseline or starting point to which practices and technologies can be compared. An LCA of a lowland production system was therefore conducted. Data for flock performance and management practices were obtained from the Teagasc National Farm Survey (Table 1). All lambs were drafted for slaughter to produce a target carcass weight of 20 kg.

GHG reduction practices/technologies are typically broken into two categories; 1) improve efficiency and 2) adopt low emission technologies. The first mitigation strategy includes improvements in soil fertility, genetic merit of flocks, animal management, flock health, and more efficient grass growth and utilisation. The second mitigation strategy involves the adoption of low emission technologies such as protected urea and the use of low emissions slurry spreading equipment. The following GHG reduction practices were investigated:

• Substituting nitrate fertiliser with protected urea (from 90% nitrate based to 100% protected urea)
• Incorporation of white clover into swards (reducing synthetic fertiliser requirement by 20%)
• Reducing concentrate feeding (103 kg per ewe to 50 kg per ewe)
• Weaning rate (1.39 to 1.5)
• Mortality rate (7.9% to 5%)

The GHG intensity of a typical lowland system was calculated as 10.8 kg CO2 equivalent /kg live weight, which is lower than the global average of 11.3. Methane contributed 66% of total GHG emissions, predominantly sourced from the digestion of feed (enteric fermentation). Nitrous oxide from fertiliser application, managed manure and manure excreted during grazing contributed a further 19% of total GHG emissions. The remaining 16% of total GHG emissions was sourced from the production of concentrate feed, fertiliser and the consumption of fossil fuels (i.e. diesel). Improving efficiency of a system typically reduces GHG emissions per unit output; however, mixed effects occur when assessing total emissions. This is the case for improving mortality and weaning rate. These measures reduced the GHG intensity by 2.2% and 4.9% respectively (Figure 3); however, total emissions remained unchanged. This is due to the greater number of animals in the system due to more live lambs weaned per ewe. As a result, reducing mortality and increasing weaning rate increased live weight sold by 3.0% and 7.4%, respectively.

Figure 3. The greenhouse gas intensity (kg CO2 equivalent /kg live weight) of a typical lowland sheep system (base) and the mitigation potential of reducing mortality, reducing concentrate feeding, reducing synthetic fertiliser by incorporation of clover into swards, use of protected urea, improving weaning rate and all combined.

Conversely, when you look at the fertiliser related strategies, incorporation of clover into swards reduced the quantity of N fertiliser needed to grow the same quantity of forage. As a result, both total GHG emissions and GHG emission intensity reduced by 2.0% and 2.4% while maintaining output (Figure 3). Similarly, the adoption of low emission technologies such as protected urea reduced total GHG emissions and GHG intensity by 5.0% and 2.4%, respectively. Protected urea has significantly lower GHG emissions per kg N applied in comparison to nitrate based fertilisers and also has significantly lower ammonia emissions than straight urea. The production and distribution of concentrate feed typically results in greater GHG emissions per kg than the same quantity of well managed fresh grass. However, to meet energy requirements, livestock forage intake increases when concentrate feeding rate is reduced. Consequently, when land area and yield is fixed, stocking rate and output is reduced. This resulted in the reduction of concentrate fed per ewe from 103 kg to 50 kg to reduce total GHG emissions and GHG intensity by 4.3% and 1.7%, respectively (Figure 3).

The combination of reducing reliance on concentrate feed, the adoption of protected urea, the reduction in N fertiliser through the incorporation of white clover into swards, and the improvement in mortality and weaning rate reduced total farm GHG emissions by 9.7%. This reduced the GHG intensity of a lowland sheep system from an average of 10.8 kg CO2 equivalent /kg live weight to 9.6 kg CO2 equivalent /kg live weight (Figure 3) while increasing carcass output from 237 kg/ha to 255 kg/ha. Further development and implementation of low emission technologies is needed to reduce the GHG intensity and total GHG emissions of sheep systems and contribute to the GHG reduction target.

Conclusion

The Irish sheep sector is starting from a good position where a typical lowland system has lower GHG intensity per kg live weight than the global average. The impact of available GHG mitigation practices independently and collectively on a typical sheep system has been calculated to reduce total GHG emissions and GHG intensity while improving the efficiency of the system. For the Irish agricultural sector to achieve the 25% GHG reduction target set by the national climate action plan the sheep sector must be proactive in adopting available GHG mitigation strategies.

Take home messages

• The Irish sheep sector directly emitted 1,065 kilotonnes CO2 equivalent in 2020, however, it also indirectly contributes to other greenhouse gas (GHG) emission sources e.g. fertiliser, fuel
• A GHG intensity of 10.8 kg CO2 equivalent per kg live weight has been calculated for a typical lowland sheep system in Ireland
• Improving the efficiency of typical sheep systems and the adoption of low emission technologies can reduce the GHG intensity to 9.6 kg CO2 equivalent per kg live weight
• Further development and implementation of low emission technologies is necessary to reduce the GHG intensity and total GHG emissions of sheep systems.