Today's level of anthelmintic use in livestock production is a major threat to both the livestock industry and the environment. In this context, the research community is looking for ways to equip farmers with preventive and treatment strategies that can decrease livestock-industry dependence on anthelmintics. Production practices for a sustainable control of parasites have been advocated for almost forty years, but farmers' uptake of these practices has been too slow to address the issues at stake. In this paper, we examine the rationales behind the underadoption of sustainable worm control practices in grassland-based livestock systems. This research builds on 25 semi-structured interviews with dairy sheep farmers in southwestern France. The interview material was analysed via qualitative discourse analysis. We highlight farmers' social representations and rationales underpinning adoption or non-adoption of the 'low anthelmintics use' strategy. We identify six profiles for nematode control according to the way each farmer included treatment and coprology in their on-farm practice. We identify that the low-use strategy has low adoption potential due to its low perceived relative advantage; low perceived trialability; unclear compatibility with previous experiences, needs, and values; and higher complexity than the status quo option. We show that holistic, pro-environmental, and collaborative attitudes are associated with adoption of the low-use strategy. We then discuss ways to improve uptake, such as increased communication, trainings, and farm visits involving farmers, extension agents and veterinarians.