Livestock products are amongst the types of food with the highest environmental loads. Furthermore, considering the life cycle stages for a livestock product from the farm to the fridge in the supermarket, it is clear that the primary production on the farm and the related inputs are responsible for the major part of the load of many impact categories (Dalgaard et al., 2007; Nielsen et al., 2003). In assessing the environmental impact of livestock products, it is thus important to have a good estimation of the impacts at the farm level. Livestock systems show a huge diversity in the way or the degree by which the livestock production is integrated with crop production, in their reliance on inputs from distant places in the world, and in housing and feeding conditions. All mentioned aspects have a huge effect on emissions related to the production. Even when livestock rearing and fattening may take place independently from land use for crops, the production of manure is of great environmental importance and it will most often have to be applied on agricultural land. Thus the aspect related to crop production and land use needs to be dealt with in assessing livestock systems, besides the particular livestock aspects. In addition, emissions related to livestock production are strongly influenced by a number of environmental factors.