There is scope for improving the sustainability of intensive dairy farms through the uptake of sustainable production practices such as more grass-based feeding systems. Such feeding systems can reduce feed-food competition and the environmental impacts of feed production, among other farm-level and societal benefits. However, empirical research on how farmers' feed choices mis(align) with sustainability transitions and the associated drivers is limited. This paper explores the trade-offs that farmers make between the environmental, social and economic sustainability impacts of grass-based feeding systems based on data from Swedish dairy farmers. Using an identity-based utility framework and a hybrid latent class model, we find substantial heterogeneity in dairy farmers' trade-offs between feed-related sustainability attributes: greenhouse gas emissions, biodiversity, animal welfare, feed self-sufficiency, feed cost and milk yield. Furthermore, our findings demonstrate that farmers who are strongly interested in the environmental and social sustainability impacts of their dairy feeding systems, beyond economic gains, are motivated mainly by their pro-environmental and pro-social identities. Overall, our findings imply that identity-enhancing interventions are promising policy instruments for encouraging the uptake of more grass-based feeding systems.