Carbon emissions from smallholder pig production in China: a precise account based on farmers' survey

Carbon emission from pig production is an issue of great importance owing to its effect on global warming. Differed from widespread large-scale pig farms in North America and Europe, small-scale and smallholder pig farms are mainly concentrated in China. However, information on carbon emissions from Chinese smallholder pig farms is limited. Additionally, large amounts of drugs and vaccines have been applied during smallholder pig production in China, yet their contribution to carbon emissions is unclear. Therefore, detailed dataset which records all inputs during a pig's entire life cycle should be obtained, so as to accurately determine the magnitude of carbon emissions from Chinese smallholder pig farms. This study took Yancheng, eastern China, as an example and adopted the carbon footprint (CF), life cycle inventory (LCI), and Intergovernmental Panel on Climate Change (IPCC) greenhouse gas (GHG) field calculations to accurately estimate the GHG emissions resulting from pig production of China. Furthermore, the contributions of vaccine application and other driving forces behind GHG emissions were identified using statistic methods. In the study area, the pig CFs in the nursery period, fattening period, and full life cycle were 5.83, 4.73, and 6.75 kg CO₂ eq·kg^-1 respectively. The CF of pig production in the study area varied from 4.74 to 9.48 kg CO₂ eq·kg^-1, with an average of 6.75 kg CO₂ eq·kg^-1; this average was, overall, higher than that of large-scale pig farms in North America and Europe. GHG emissions from manure (42.87%) and fodder (27.77%) were responsible for a large proportion of the total CF. Normal vaccine inputs contributed highly (15.33%) to the total CF. The contribution of vaccine application to the CF is roughly evaluated, suggesting it may be a potentially important source of GHG emissions in pig production and should receive more attention in the future. Furthermore, GHG emissions from smallholder pig production farms can be significantly reduced by developing a mixed crop-livestock system, increasing the application of organic fertilizers, and installing biogas digesters.