Impact of Dietary Protein Source on Life Cycle Assessment of UK Pig Production

Crop production for feed is the main contributor to environmental impacts of pig production systems, according to K.L. Stephen in her thesis from 2011. The results of her study suggest there is scope to lower the overall environmental impact by using home-grown peas, beans or lupins as the main protein source, rather than imported soybean meal.
calendar icon 27 July 2012
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A Life Cycle Assessment (LCA) was developed to evaluate the environmental impacts of producing one kilo of pig live weight, explained Katie Louise Stephen in her Masters of Philosophy thesis at the University of Edinburgh in 2011.

She compared dietary protein sources, i.e. imported soybean meal with the UK protein sources (1) peas, (2) beans and (3) lupins. A holistic approach was used and the LCA was developed using several sub-models to include all processes within the system boundaries for pigs grown from 12kg to 106kg.

Two UK sites were modelled – East Anglia and Yorkshire – each with individual site conditions and a comparison of the two sites was included using a common soil type present at both sites. A Brazilian corn-soya rotation was simulated for the production of soybean meal. Individual soil and climate conditions were defined at each site and two fertiliser scenarios were modelled: synthetic and slurry.

The environmental impacts assessed were (1) Global Warming Potential (GWP), (2) eutrophication and (3) acidification.

Differences occurred between diet and sites but also between fertiliser scenarios. It was concluded that the GWP per kg pig in the slurry fertiliser scenario are consistently higher.

The bean-based diets resulted in the lowest GWP, ranging from 1.85 to 2.67kg carbon dioxide (CO2) equivalent100 and the soya-based diets had the highest GWP per kg pig, 2.52 to 3.08 kg CO2 equivalent100.

Diet production contributed the most to GWP per kg pig, i.e. 63.9 to 78.5 per cent. Transport contributed approximately one per cent to GWP for the home-grown diet scenarios but in the soya-based diets this was on average three per cent.

Eutrophication potentials were higher in the synthetic fertiliser scenario. The lupin-based diets consistently had the highest eutrophication potential, 0.056 to 0.133kg phosphate (PO4) equivalent in both fertiliser scenarios. Whereas the pea-based diets were consistently associated with the lowest eutrophication potential at 0.049 to 0.103kg PO4 equivalent.

The soya-based diets were associated with the highest acidification potential, 0.054 to 0.129kg sulphur dioxide (SO2) equivalent in both fertiliser scenarios.

The results were weighted from the lowest to highest results for each impact category for each diet scenario at each site by Ms Stephen.

In her conclusions, Ms Stephen reports that the work highlighted that crop production is the main contributor to environmental impacts of pig production systems.

It has also been identified that the fertiliser scenario is important to consider when efforts are being made to reduce the environmental impacts within the management system. This has highlighted:

  • the importance for pig production systems to utilise slurry efficiently by considering crop nutrient requirements, and
  • the relevance of minimising the amounts of applied synthetic fertilisers.

This LCA has used a novel approach to model the environmental impacts of UK pig production systems, she continued. To allow detailed calculation of the environmental impacts associated with one kilo of pig by modelling specific sites within the UK.

There may also be scope to lower the environmental impacts per kilo of pig by considering the environmental impacts of the feed ingredients used in diet formulations, whilst still meeting the nutrient requirements of the pig.

Ms Stephen’s overall conclusion is that UK legume-based diets are associated with a lower environmental impact per kilo of pig than a conventional soya-based diet, which result with the highest environmental impacts per kilo of pig. The bean-based diets had the lowest environmental impacts per kilo of pig and the soya-based diets had the highest, with the pea- and lupin-based diets having equal and intermediate environmental impacts.


Stephen K.L. Life Cycle Assessment of UK Pig Production Systems: Impact of Dietary Protein Source. Masters of Philosophy thesis. University of Edinburgh, Scotland. 2011

Further Reading

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July 2012
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