Mixed crop–livestock farming is usually considered to be beneficial for the environment, but the comprehensive characterisation of functional interactions between crops and livestock, and thus the assessment of their ecological relevance, remain problematic. In this article, we design a systemic reading grid focusing on the agricultural practices of crop–livestock interactions, which we organised in four groups according to the agronomic functions they fulfil and the ecological processes involved: (i) animals are used as a source of mechanical energy; (ii) rangelands and permanent grasslands, serving as a source of biomass to manage fertility, are spatially interwoven into the cultivated fields; (iii) on those cultivated fields, non-fodder crops are rotated/associated with fodder crops; (iv) the livestock consume locally produced fodder, grain and straw, and their excreta are spread on cultivated plots. Based on 86 interviews with retired and active farmers, we applied this grid to study the dynamics of crop–livestock integration in a small French agricultural region since 1950. We show that even though the number of mixed crop–livestock farms remains quite high, there has been a massive impoverishment of crop–livestock interactions within these farms. We discuss this trend and the contributions made by the reading grid.