Attributional versus consequential life cycle assessment and feed optimization: alternative protein sources in pig diets

Feed production is responsible for the majority of the environmental impact of livestock production, especially for monogastric animals, such as pigs. Some feeding strategies demonstrated that replacing one ingredient with a high impact, e.g. soybean meal (SBM), with an alternative protein source, e.g. locally produced peas or rapeseed meal, has potential to reduce the environmental impact. These studies, however, used an attributional life cycle assessment (ALCA), which solely addresses the direct environmental impact of a product. A replacement of SBM with alternative protein sources, however, can also have indirect environmental consequences, which might change environmental benefits of using alternative protein sources. This study aims to explore differences in results when performing an ALCA and a CLCA to reduce the environmental impact of pig production. We illustrated this for two case studies: replacing SBM with rapeseed meal (RSM), and replacing SBM with waste-fed larvae meal in diets of finishing-pigs. We used an ALCA and CLCA to assess global warming potential (GWP), energy use (EU) and land use (LU) of replacing SBM with RSM and waste-fed larvae meal, for finishing-pigs. The functional unit was 1 kg of body weight gain. Based on an ALCA, replacing SBM with RSM showed that GWP (3%) and EU (1%) were not changed, but LU was decreased (14%). ALCA results for replacing SBM with waste-fed larvae meal showed that EU did not change (1%), but GWP (10%) and LU (56%) were decreased. Based on a CLCA, replacing SBM with RSM showed an increased GWP (15%), EU (12%) and LU (10%). Replacing SBM with waste-fed larvae meal showed an increased GWP (60%) and EU (89%), but LU (70%) was decreased. Furthermore, the results of the sensitivity analysis showed that assumptions required to perform a CLCA, such as definition of the marginal product, have a large impact on final results but did not affect the final conclusions. The CLCA results seem to contradict the ALCA results. CLCA results for both case studies showed that using co-products and waste-fed larvae meal currently not reduces the net environmental impact of pork production. This would have been overlooked when results were only based on ALCA. To gain insight into the environmental impact of feed, animal nutritionists can use an ALCA. If policy makers or the feed industry, however, want to assess the net environmental impact of a potential feeding strategy, it is recommended to perform a CLCA. Feed and food markets are, however, highly dynamic. Pig feed optimization is based on least cost optimization and a wide range of ingredients are available; diet compositions can, therefore, change easily, resulting in different environmental impacts. Ideally, therefore, a CLCA should include a sensitivity analysis (e.g. different feed prices or different marginal products) to provide a range of possible outcomes to make the results more robust.