In Northern Ireland, grazed grass is the main diet offered to dairy cattle throughout the summer months. Whilst the Holstein-Friesian (HF) dairy cow is extremely efficient at converting grass into milk, there is evidence that the incidence of infertility in this breed is increasing (Mayne et al. 2001). This may reflect the fact that the breeding goals for the HF breed have been based primarily on selection for milk production with little emphasis for other traits such as fertility or health. In contrast, Norwegian dairy cattle (NC) have been selected using a multi trait index, with less emphasis on milk production and inclusion of other fertility and health traits. The overall objective of the present study was to evaluate the effect of varying stocking rate at pasture on performance of these two contrasting breeds.