The UK Biodiversity Action Plan identifies upland heath and blanket bog as priorities for conservation. Heavy grazing by livestock has damaged these habitats in many parts of the UK. Agri-environment schemes have partly addressed the problem by encouraging farmers to reduce sheep stocking levels on degraded moorland. This can prevent further loss of dwarf shrub cover, but the increased biomass of moorland grasses can inhibit regeneration of dwarf shrubs and other desirable species. The objectives of this system-scale study are to assess the impact on plant species composition and animal performance, of sheep-only and mixed grazing regimes with both cattle and sheep on degraded wet heath vegetation. It is being carried out as part of a wider project to determine environmentally sustainable and economically viable grazing systems for heather moorland.