This paper addresses the potential of sustainability improvement by increased efficiencyin milk and cattle production. The experience of Swedish improvement over the last half centuryreveals the global potential for the sustainable management of land use, nutrition balance andbioenergy supply.Ruminants are an important part of the global food production system. Ruminantproduction has the potential to substantially increase land area available for bioenergy production.They can use energy in foodstuffs with none human nutritive value and simple nitrogencompounds in the production of high quality feeds. They can convert renewable natural resourcesfrom ecosystems, that otherwise have low capacity to transform solar energy fluxes to food, tohigh quality food.Globally, the area of pasture is 2.5 times larger than the area of cropland. Ruminants arean important part of the global food system, supplying human energy metabolism. Due to thecompetition for land, the skilfulness in rumen production affects potentials for green energyproduction supplying the energy metabolism in the technical systems of society.This paper discusses two aspects of ruminant production affecting the potential for greenenergy production:(i) The impact of increased nutritional physiological efficiency, i.e., better feedingstrategies, and(ii) The importance of utilising ruminants as ruminants, where they transform solar energyfluxes to high quality foodstuffs from ecosystems with low capacity to produce food throughother paths.The focal point is the impact on the land remaining for green energy production supplyingthe technical systems of society, after food supply needs are met. Estimates are provided on theimpact on other sustainability aspects at different system levels as well as in the threesustainability-dimensions. The results are provided through the application of a methodologywithin the frame of integrated assessment for analysis of sustainability effects in systems withmutual dependencies between systems and system levels. This is of general interest as amethodology, supporting the development of sustainable green energy production and meetingthe needs of society. It contributes with concrete results, supporting an increased sustainableproduction of green energy due to increased efficiency within a sector that competes for land