The question of technical innovation has always been the core of livestock development policies and projects in Africa. However, long term observations show that in some cases, proposed innovations have failed and that unexpected changes have occurred. Systemic approaches (namely the literature on Marketing Systems and Systems of Innovation) may help in understanding the way livestock societies evolve in relation with technical constraints, economic contexte and socio-political factors. In the case of the Chadian dairy sector, the use of complementation by producers is limited by market imperfection in the coton-seeds and groundnut cakes marketing chains. However, the emergence of urban fermented milk retailers has been permitted by the development of motorised milk transportation (motocycles). Changes in consumption lead to the use of endogenous techniques (mini-dairies) and local quality standards (such as "lait pur de vache"). In Ethiopia, the use of cross-bred cows is limited to peri-urban areas. The importance of butter in the cultural heritage remains in the urban culture, which explains the importance of the cosmetic butter market. These 2 case-studies show that the development of livestock societies relies on the capacity of local actors to integrate endogenous innovations in their individual and collective projects. (Texte intégral)