Insights into carbon and nitrogen footprints of large-scale intensive pig production with different feedstuffs in China

Through the whole process of large-scale pig production, feed production puts great environmental pressure in terms of greenhouse gas (GHG) emissions and nitrogen (N) emission. Additionally, different feedstuffs will have different results. While previous studies seldom analyzed carbon footprint and nitrogen footprint from feed components or diet choices. Thus, we selected China, the largest producer and consumer of pork in the world, to analyze both nitrogen footprint and carbon footprint through the life cycle of pig production with different feed components. We used life-cycle environmental footprint and scenario analysis to compare carbon footprints, nitrogen footprints, and feed prices of large-scale pig production with different feedstuffs in China. The life cycle of the pig production includes feed crop cultivation, feed processing, pig raising, and manure management. The functional unit is the weight of 1 kg of live pig. The results showed that the carbon footprints, nitrogen footprints, and feed prices ranged from 1.67 kg CO₂-eq FU⁻¹ to 1.70 kg CO₂-eq FU⁻¹, 35.3 g Nr FU⁻¹ to 38.9 g Nr FU⁻¹, and 1.42 CNY kg ⁻¹ to 2.15 CNY kg ⁻¹, respectively. Feed crop production and manure management contributed the largest carbon footprint (54%) and the largest nitrogen footprint (64%), respectively. The four scenarios exhibited various results. Scenario 3 (S3), substituting soybean meal in the original feed with distillers dried grains with soluble (DDGS), presented a more favorable outcome with respect to carbon and nitrogen footprints as well as feed prices. This was mainly attributed to feed crop cultivation, manure management, crude protein contents of feeds, and prices of the feed crops. Concerning the uneven feed crop production, number of pig farrowed, feed consumption, and inter-provincial transportation across China, we conducted the spatial analysis under the optimal S3. It revealed that the northern provinces in China exhibited both higher carbon and nitrogen footprints than the southern provinces, due to the northern regions cultivating the crop feed. Finally, we proposed recommendations from perspectives of cultivation practice, feed adjustment, manure management, and strategic zoning. The study not only highlighted the importance of environmental footprint for analyzing environmental impacts of pig production, but also provided the implications for enhancing the sector’s environmental sustainability from perspective of feed adjustment.