Impact of organic pig production systems on CO2 emission, C sequestration and nitrate pollution

Organic rules for grazing and access to outdoor areas in pig production may be met in different ways, which express compromises between considerations for animal welfare, feed self-reliance and negative environmental impact such as greenhouse gas emissions and nitrate pollution. This article compares the environmental impact of the main organic pig systems in Denmark. Normally, sows are kept in huts on grassland and finishing pigs are raised in stables with access to an outdoor run. One alternative practice is also rearing the fattening pigs on grassland all year round. The third method investigated was a one-unit pen system mainly consisting of a deep litter area under a climate tent and with restricted access to a grazing area. Using life cycle assessment (LCA) methodology, the emissions of greenhouse gases of the free range system were estimated to be 3.3 kg CO2-equivalents kg−1 live weight pig, which was significantly higher than the indoor fattening system and the tent system, yielding 2.9 and 2.8 kg CO2-eq. kg−1 pig, respectively. This was 7–22% higher compared with Danish conventional pig production but, due to the integration of grass-clover in the organic crop rotations these had an estimated net soil carbon sequestration. When carbon sequestration was included in the LCA then the organic systems had lower greenhouse gas emissions compared with conventional pig production. Eutrophication in nitrate equivalents per kg pig was 21–65% higher in the organic pig systems and acidification was 35–45% higher per kg organic pig compared with the conventional system. We conclude that, even though the free range system theoretically has agro-ecological advantages over the indoor fattening system and the tent system due to a larger grass-clover area, this potential is difficult to implement in practice due to problems with leaching on sandy soil. Only if forage can contribute to a larger proportion of the pigfeed uptake may the free range system be economically and environmentally competitive. Improvement of nitrogen cycling and efficiency is the most important factor for reducing the overall environmental load from organic pig meat. Presently, a system with pig fattening in stables and concrete-covered outdoor runs seems to be the best solution from an environmental point of view.