Breeding goals differ for different breeds of dairy cattle. For example the breeding programmes for Holstein-Friesian (HF) animals have been based primarily on improved milk production with little emphasis on functional traits such as fertility. In contrast, Norwegian (NC) dairy cattle have been bred using a multi-trait selection procedure for 25 years. These differences in selection procedures for the two breeds may have major effects on overall herd output and profitability with the forage-based systems of milk production employed in Northern Ireland. The objective of the present paper is to present the effects of two levels of nutrient input on food intake and utilisation, and animal performance of the two breeds, with diets based on grass silage during the first and second lactation.