Protein self-sufficiency and the preservation of the environment are two objectives for which society is presently strongly yearning. As regards the feeding of ruminants, protein self-sufficiency cannot be conceived outside a global feed self-sufficiency of the animals, in view of the narrow interactions existing between energy and protein in the diets. Concerns for the environment are sometimes convergent and synergic with the striving for feed self-sufficiency. They regard territories the limits of which can be quite different from those defined for the quality labels of the produce. Thus the specialization of livestock rearing on the one hand and of cereal crop growing on the other requires the finding of complementarities and co-operations among farms that co-exist on the same territory. The emergence of new organizational types of agricultural activity implies public policies with well-defined targets. At stake is the future of the so-called mixed crop - livestock farm regions, where the maintenance of a diversity of land-use patterns and of production systems remains the means to a sustainable rural development.