Livestock farming is a traditional and important contributor to the rural economy in the hills and uplands of the UK. However, significant areas of the uplands have seen a decline in the condition of heath and mire habitats and the loss of dwarf shrubs as a result of over-grazing. Attempts to halt the decline and improve the condition of upland heath and mire habitats have been undertaken by the introduction of agri-environment schemes. In the main, such schemes rely on the reduction of sheep numbers. However, recent Defra funded research (LS1508) has indicated that this can result in dominance by competitive and/or unpalatable species such as purple moor-grass (Molinia caerulea ) or mat-grass (Nardus stricta ), leading in time to a reduction in the physical and financial performance of the flock. The objective of this study is to assess the impact of cattle grazing on Nardus stricta dominated pasture on sheep and cattle performance. It is being carried out as part of a wider project to determine environmentally sustainable and economically viable grazing systems for heather moorland.