Life cycle assessment of UK pig production systems: the impact of dietary protein source

Abstract

A Life Cycle Assessment (LCA) was developed to evaluate the environmental impacts of producing 1 kg pig live weight. A comparison was made between 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 12 kg to 106 kg. 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 fertilizer 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 fertilizer scenarios. It was concluded that the GWP per kg pig in the slurry fertilizer scenarios are consistently higher. The bean based diets resulted in the lowest GWP ranging from 1.85 to 2.67 kg CO2 equivalent100 and the soya based diets with 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 – 78.5 %. Transport contributed approximately 1% to GWP in the home grown diet scenarios, however in the soya based diet scenarios, this was on average 3 %. Eutrophication potentials were higher in the synthetic fertilizer scenario. The lupin based diets were associated with the highest eutrophication potential, 0.056 – 0.133 kg PO4 equivalent in both fertilizer scenarios. Whereas the pea based diets were consistently associated with the lowest eutrophication potential, 0.049 to 0.103 kg PO4 equivalent. The soya based diets therefore concluded with the highest acidification potential, 0.054 to 0.129 kg SO2 equivalent in both fertilizer scenarios. The results were weighted from the lowest to highest results for each environmental impact category for each diet scenario at each site. The overall conclusion is that the bean based diets have the lowest and the soya based diets have the highest environmental impacts per kg pig. Both the pea and lupin based diets were concluded to have equal environmental impacts per kg pig.