Knowledge of Gas emissions in pig breeding

Abstract

This paper summarises the «Porcherie verte» programme in terms of knowledge and control of gas emissions occurring during the different phases of pig breeding. These emissions include green house gases, methane (CH4) in particular and nitrous oxide (N2O), as well as ammoniac (NH3), harmful for animals and man and having an impact on the environment in terms of acidification and eutrophication. NH3 emissions have been modelled for breeding buildings on wood slats. These emissions can be decreased by decreasing protein content of feed distributed to animals or by frequently renewing the manure in the buildings. The biological treatment of manure reduces these emissions, especially when there is no phase separation. The mixing of manure in storage tanks favours it. NH3 emissions vary strongly depending what substrate is used for litter and management. During composting, they also depend on the initial characteristics of the substrate composted, but also on the technique used.

NO2 emissions are generally higher with litter than with wood slate, but there are high variations depending on management. Composting can also lead to NO2 emissions, particularly with thin layers. When biological treatment of manure is used, these emissions are low but depend on the ventilation technique used. In the soil, NO2 emissions are not higher after adding animal waste than after adding mineral fertilisers and they are difficult to quantify.

CH4 emissions are lower on litter than on wood slats. They are also low with composting, except when thin layers are used. Biological treatment of manure leads to an important reduction in emissions as compared to storage. Litter and composting are often thought by the public to have a lower impact on the environment than manure. We have, however, shown that they generate more green house gases either directly (as N2O emissions) or indirectly (wasting of nitrogen fertilisers whose synthesis requires high amounts of energy). This is often accentuated since men try to lower costs by increasing animal density or decrease hay quantity used as a substrate for composting. Similarly, biological treatment of manure, which at first seems to have a favourable impact since it leads to lower NH3 emissions without releasing too much N2O, actually has a poor environmental balance since it requires high amounts of energy either directly or indirectly (fertiliser waste). Indeed, there is twice as much pollution, in the soil and from water to the atmosphere on the one hand and from the farm to the environment on the other hand.