In North Cameroon, the current status of cattle breeding is illustrative of the studies that showed that extensive farming often evolves under pressure such as the lack of resources (Cochet, 2001; Tiffen et al., 1994). To meet challenges raised by the shortage of pasture land, livestock farmers elaborate defensive strategies (settlement, reduction of the herd, diversification of activities) which are alike to those observed in West Africa where the phenomenon is already underway. The defensive strategies of farmers are well known, but there is a lack of knowledge about their responses to the development of market, caused by the increase of external beef demand (Nigeria) and particularly local demographic trends: the growth rate is + 2.8% per year in north Cameroon, and the population of Garoua, the main provincial town, is actually estimated at 370,000 inhabitants will possibly double within 15 years. It has been found that, when conditions are favourable, farmers modify their practices to respond to opportunities generated by good market trends (Cour, 2000). The support of this innovative capacity, which is seen as one of the main operational levers to meet the challenge of food security, raises two important questions: 1) what is the impact of market on livestock farmer's practices? 2); how does the evolution of livestock in the above context influence beef supply? This communication presents a methodological approach for the study of livestock dynamics interacting in market forces.