Experts at Teagasc have been using life cycle assessment, an internationally-recognised methodology, to calculate the environmental performance of average sheep systems in Ireland and to determine the effect of recommended practices.
Ireland is the largest net exporter of sheepmeat within the European Union, with the sheep sector generating approximately €300 million every year. However, as with all food production systems, sheep systems can have negative environmental effects. The most pressing in the current climate is 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 eat – particularly livestock products – is produced. Their purchasing decisions are 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 must identify and adopt practices that are environmentally sustainable, economically viable and socially acceptable.
Emissions from the sheep sector
In the most recently reported year, 2020, Ireland emitted 58,766 kilotonnes (kt) CO2 equivalent, of which more than one-third came from the agricultural sector. The digestion of feed and the release of methane (enteric fermentation) dominates agricultural emissions, contributing 61.4%.
The remaining GHG emissions are predominantly associated with manure and synthetic fertiliser application. Sheep directly emitted 1,065kt CO2 equivalent through the digestion of feed and manure management. The sheep sector is also indirectly responsible for GHG emissions from the use of synthetic fertilisers, fuel and electricity, which are recorded separately.
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 with 2018 levels. For the agricultural sector to achieve this, adoption of recommended practices and the identification of new technologies are required at farm level.
Life cycle assessment modelling
Life cycle assessment (LCA) is an internationally-recognised methodology that has been widely adopted in agriculture to calculate the environmental impact of a farming system and its products. Researchers in Teagasc have developed LCA models for sheep systems in Ireland. These models adopt a cradle-to-farm-gate boundary, meaning all GHG emissions up to the point at which the product (lambs, ewes or wool) leaves the farm are accounted for. On-farm emissions counted and emissions released during the production of farm inputs (i.e. fertilisers, electricity, concentrate feed) are recorded.
By applying this boundary, a LCA can identify the key GHG sources and management practices that have potential to reduce GHG emissions. To determine the GHG reduction potential of proposed management practices and emerging technologies, 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.
A LCA of a lowland production system was conducted. Data for flock performance and management practices were obtained from the Teagasc National Farm Survey (Table 1).
Measuring GHG reduction methods
GHG reduction practices and technologies are typically broken into two categories: improve efficiency; and adoption of low-emission technologies. 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 (103kg/ewe to 50kg/ewe);
Increasing weaning rate (1.39 to 1.5);
Reducing lamb mortality rate (7.9% to 5%).
The GHG intensity of a typical lowland system was calculated as 10.8kg CO2 equivalent/kg live weight, which is lower than the global average of 11.3.
Table 1. Description and performance of an average lowland sheep system
Lowland system
Ewes 140
Stocking rate (ewes/ha) 7.8
N fertiliser (kg N/ha) 73
Lambing period March
Replacement rate (%) 25
Weaning rate (lambs/ewes) 1.39
Concentrate (kg/ewes) 103
Carcass output (kg/ha) 237
Methane contributed two-thirds (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 15% of total GHG emissions were sourced from the production of concentrate feed, fertiliser and the consumption of fossil fuels (diesel).
Improving the efficiency of a system typically reduces GHG emissions per unit output. However, there are mixed effects when assessing total emissions. This is the case for improving mortality and weaning rate. Both measures reduced the GHG intensity – by 2.2% and 4.9%, respectively – but total emissions remained unchanged. This was due to the greater number of animals in the system because more live lambs were weaned per ewe. As a result, reducing mortality and increasing weaning rate increased live weight sold by 3.0% and 7.4%, respectively.
Conversely, when you look at fertiliser-related strategies, improving soil fertility and incorporating clover into swards reduced the quantity of nitrogen 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%, respectively, while maintaining output.
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 with nitrate-based fertilisers and also significantly lower ammonia emissions than straight urea.
Research Officer Jonathan Herron said: “The production and distribution of concentrate feed typically results in greater GHG emissions per kilogram than the same quantity of well-managed fresh grass. 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 103kg to 50kg to reduce total GHG emissions and GHG intensity by 4.3% and 1.7%, respectively.
Evidence of emissions reduction
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 a base of 10.8kg CO2 equivalent/kg live weight to combined 9.6kg CO2 equivalent/kg live weight, while increasing carcass output from 237kg/ha to 255kg/ha. Further development and implementation of low-emission technologies is required to reduce the GHG intensity and total GHG emissions of sheep systems and contribute to the GHG reduction target.
“The Irish sheep sector is starting from a good position,” concluded Jonathan, “where a typical lowland system has lower GHG intensity per kg live weight than the global average. 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.”
Photo of sheep in a field
Emissions reduction
A number of practices and technologies can reduce total farm emissions.
5% reduction of total greenhouse gas emissions when protected urea technology is adopted.
4.3% reduction of total greenhouse gas emissions when land area and yield is fixed and stocking rate and output is reduced, resulting in the reduction of concentrate fed per ewe from 103kg to 50kg.
2% reduction of total greenhouse gas emissions through improved soil fertility and by incorporating clover into swards to reduce the quantity of N fertiliser needed.
9.7% reduction of total farm greenhouse gas emissions through a 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.
Source: EMM/ The Agriculture and Food Development Authority
