Overall evaluation of pig production systems and their optimisation on the farm level

Abstract

This paper summarises the contributions made by the «Porcherie verte» programme in the overall integrated evaluation of pig production systems, considering on different scales the different pertinent aspects of sustainability, beyond environmental impact. The multiple criteria comparison of two types of breeding management considers all the aspects of sustainability (environment, society, economy) but at a level restrained to pig breeding. Pigs raised on litter with access to a small courtyard have better welfare, better growth performances but with fatter carcasses than pigs raised on wood slats. Their meat has a poorer technological quality but a better sensorial quality. This type of management produces less unpleasant odours but is more costly. The products can, however, be better valorised by a label.

Modelling aimed at optimisation of a farm considers the environmental and economic aspects, but not those of society, when comparing the different ways to manage waste. The scale of the approach is larger than in the preceding study, considering the interactions between animal and plant production on the farm’s property, which corresponds to a fundamental decision scale in agriculture. The «raw manure» waste management leads to an improved gross margin, with good environmental balance, but the production is limited to 60 pigs per hectare. The biological treatment of manure without phase separation allows increasing pig production but deteriorates the phosphorus balance of the farm and significantly reduces the gross margin per pig produced. Phase separation before biological treatment of manure allows an increased pig production that respects environmental phosphorus constraints, but it decreases the gross margin per pig produced. Manure composting can be an alternative to biological treatment for small farms, but its environmental balance is poor. Exporting manure compost slightly improves the apparent N and P balances of the farms but does not change gas emissions. It allows maintaining good gross emissions, even with high numbers of animals. Pig breeding on litter allows the production of more pigs/ha but is unfavourable for the environmental impact and increases production costs. Composting litter manure increases pig production per ha but only in the absence of environmental constraints on phosphorus and the growth of the gross margin is low. Exporting the compost surplus allows increasing pig production by lowering the apparent N and P balances, but not gas emissions. Biological treatment seems to give the best compromise between gross margin and environmental impact amongst the different types of treatment that allow a large number of animals, as long as one does not consider the impact of transfers outside of the farm. Amongst the different types of treatment with exportation that allow very high population levels, the composting of manure seems to cumulate the disadvantages in terms of gross margin and environmental impacts, if one neglects the impact of transfers outside of the farm associated with biological treatment.

The global evaluation of environmental impact of pig farms is restrained to the environmental aspects but its scale of approach integrates all the impacts associated with the processes upstream of the farm. The analysis of the life cycle (ACV) is a method of choice to do this evaluation and was developed for the comparison of the environmental impacts of the three contrasted scenarios of pig production. The most intensive production according to the scenario of good agricultural practices has the lowest impact on climate change, but the highest impact on acidification. Biological production that is not intensive uses a large surface but has a lower impact on eutrophisation.