Until relatively recently, breeding programmes for Holstein Friesian (HF) dairy cattle have focused selection procedures on increasing milk output with little emphasis on secondary traits such as fertility. As a result the fertility of the Holstein Friesian dairy animal is currently declining in the UK. This decline in fertility causes particular problems in seasonal calving dairy herds, where compact calving is crucial to overall performance of this system. In the Norwegian dairy cattle (NC) breeding programme, emphasis has been placed on a multi trait selection procedure including fertility and disease resistance. There is evidence that this selection procedure has resulted in improved fertility within the NC population. The present study is part of an overall programme comparing the performance of HF and NC cattle with respect to food intake, animal performance, nutrient utilisation, behaviour, health, fertility and longevity. The objective of the present study was to investigate possible differences in fertility between the two breeds when offered either a high or a low nutrient input diet based on grass silage.