Partial replacement of soybean meal with soybean silage and responsible soybean meal in lactating cows diet: part 2, environmental impact of milk production

Soybean meal, the main protein source for livestock in Italy, is associated with high environmental impact in terms of land use change. Thus alternative protein sources are advisable. The study aimed to evaluate through a Life Cycle Assessment (LCA) approach the environmental impact of milk production systems characterised by different diets of lactating cows including different sources of soybean. Four scenarios were identified: (1) conventional soybean meal (CON), (2) conventional soybean meal and soybean silage (SBS), 3) responsible soybean meal defined by the FEFAC guidelines (CON + RSM), (4) soybean silage and responsible soybean meal (SBS + RSM). Inventory data were derived from a previous in vivo trial on lactating cows and farmer interviews. Secondary data were obtained from the ECOINVENT® and the Agri-footprint databases. The LCA was performed using the SimaPro V 8.3. Soybean silage showed higher global warming potential (GWP), marine eutrophication and human toxicity compared with lucerne hay, the most utilised self-produced protein feed, due to the high contribution of mechanical operations in the field. The GWP of milk (kg CO2eq/kg FPCM) decreased from 1.38 of the CON scenario to 1.17 of SBS and 1.13 of CON + RSM; the best result was obtained by combining soybean silage with responsible soybean meal: 1.01. Furthermore, the scenarios using RSM reduced agricultural land occupation and natural land transformation. The inclusion of SBS and RSM is an interesting option to reduce environmental impact of milk production, maximising yields of DM and CP per hectare and representing an alternative protein source.HIGHLIGHTS The ration of dairy cows represents one of the main causes of the environmental impact of the livestock sector due to the impact for feed production (forage and concentrate) Feeding soybean meal as protein source has high environmental impact since it is linked with deforestation in South America Alternative protein sources like soybean silage and soybean meal produced sustainably could reduce the environmental impact of the sector.