The combination of crops and livestock can help reduce the negative impact of agriculture on the environment. Forage crops can be included in the rotation of non-fodder crops and play an important agronomic role, thus reducing the use of chemicals; if animals consume locally produced feed, nutrient flows can be more closed. The decline in the number of mixed crop-livestock farms and the factors behind this decline have been documented in many regions. However, some authors advocate going beyond the criterion of mixed crop-livestock farming and taking into account the functional interactions themselves. In this study, we aim at studying the recent transformations of crop-livestock interactions at the scale of a small agricultural region and at understanding their origin. To trace these interactions and their ecological roles, we had to reconstruct the overall functioning of past and present farms in a region of southwestern France. The required data were collected through 80 interviews to retired and active farmers. In 1955, most of the farms were mixed-crop-livestock farms, self-sufficient in feed and bedding, with forages included in the rotations. From 1960 onwards, the specialization of farms into livestock farms and grain farms isolated crops from livestock, which on the one hand separated forage and non-forage crops in distinct farms and on the other hand created open flows of concentrates between farms and even to beyond the region. However, crop-fodder rotations vanished on many mixed farms: indeed, some of them no longer have ruminants, but only monogastric animals. Besides, in farms with cattle, fodder and cereal crops are often produced on separate lands. We then explain these changes by the evolution of prices, policies, the development of irrigation infrastructures, and the soil and climate characteristics of the area.