This chapter reviews the interactions between plants and animals that govern the production efficiency of temperate pasture-based livestock production systems. These interactions operate at different temporal and spatial scales, and are highly variable. We take as our case study the dry matter intake (DMI) of animals grazing pasture because DMI is central to most of the interactions. We consider management, plant, sward and animal factors affecting DMI, and review management practices and plant breeding objectives that have sought to increase it. We conclude that there is very limited scope to alter DMI in pasture-based production systems operating near the optimum for long-term financial and environmental sustainability. Rather we propose that plant breeding should focus on plant structural characteristics that favour consistent attainment of optimal post-grazing herbage mass because we can be confident this will increase total herbage accumulation, pasture utilisation and herbage nutritive value.