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

Abstract

Purpose 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. Methods 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. Results and discussion 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. 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. Responsible editor: Greg ThomaElectronic supplementary material The onlin...

Consequential life cycle assessment of miscanthus livestock bedding, diverting straw to bioelectricity generation

“…There is some uncertainty about the quantity of miscanthus needed to replace straw bedding. If chopped and dried to moisture contents of 25% and below, miscanthus could replace straw bedding on a 1:1 basis (AHDB, 2018;Van Weyenberg et al, 2015). Preliminary studies on absorbency at Aberystwyth are suggesting that miscanthus could replace wheat straw by around 1.6:1 while some of the hardier, upland varieties bred at IBERS could be as low as 1.2:1 due to better texture and lower initial moisture content (M. Fraser, personal communication, October 2, 2018).…”

“…Crucially, lack of market has been a major reason cited by livestock farmers for not cultivating miscanthus (Wilson et al, 2014), alongside years of failed energy crop policies (Adams & Lindegaard, 2016). However, the recent demonstration of miscanthus' efficacy as a bedding material (AHDB, 2018;HCCMPW, 2010;Van Weyenberg et al, 2015) paves the way for a new market on the doorstep of livestock farms, where the opportunity costs of cultivating miscanthus are much lower than on arable farms where gross margins per hectare are significantly higher (FBS, 2018). Numerous other factors are likely to favour alternative bedding materials such as miscanthus.…”

“…Farmers' attitudes towards miscanthus cultivation and general sustainability will play a key role in the adoption of miscanthus bedding. Farmers may decide to grind miscanthus into finer bedding particles, which would require grinding equipment, and are not considered in this study (Van Weyenberg et al, 2015). Farmers are resourceful and could modify their farm systems in a multitude of ways following the introduction of miscanthus bedding, which may influence environmental outcomes in unpredictable ways (Henriksson, Flysjö, Cederberg, & Swensson, 2011).…”

“…CLCA expands the boundaries of analysis to reflect direct and indirect changes associated with a particular intervention, in terms of stages and scales of production elsewhere (Yang, ). LCA modelling has been widely applied to analyse the environmental footprint of bioenergy from straw or miscanthus (Brandão, Milà i Canals, & Clift, ; Monti, Fazio, & Venturi, ; Nguyen, Hermansen, et al, ; Parajuli et al, ; Styles, Gibbons, Williams, Stichnothe, et al, ), more recently including consequential LCA to evaluate the wider environmental effects of bioenergy and agricultural system interventions (Plevin et al, ; Styles, Gibbons, Williams, Stichnothe, et al, ; Tonini, Hamelin, Wenzel, & Astrup, ; van Zanten, Bikker, Meerburg, & Boer, ). However, we are not aware of any published studies that have applied LCA to miscanthus as a bedding material, nor to consider the consequences of new bedding materials diverting straw bedding towards bioenergy generation.…”

“…Efforts by the livestock industry to address this issue have given rise to trials of alternative bedding materials such as woodchips, miscanthus, paper, bracken and reed canary grass among others (HCCMPW, 2010). Among these alternatives, miscanthus bedding is used because of its highly absorbent nature compared with other bedding materials and its usefulness in keeping the animals clean and warm (HCCMPW, 2010;Van Weyenberg et al, 2015). It can be cultivated on lower quality agricultural land than cereal straw, as is typical in regions where livestock are common, achieve good yields with low inputs and could supply farmers with enough bedding material for their livestock needs (McCalmont, 2018).…”