Determining the competitive position of dairy farms depends on several technological, economic and institutional variables. Among them, are remarkable those related to animal feeding in the current context of high variability on prices. In this context, the aim of our study is to analyze the effects on milk supply and the competitiveness of dairy farms with different models of land intensification, with greater reliance on market purchases or self production of livestock feed. Our work is based on an econometric approach to a variable cost function, in a fixed effects model for unbalanced panel data of specialized dairy farms in Navarre (Spain). From this region, we use 3 geographical areas in relation to the availability of grazing land. It has been tested the absence of sample selection bias and satisfaction of regularity conditions. The study shows a flexible milk farm supply with respect to the price of milk and very dependent on the evolution of feed prices. This aspect has been emphasized by the restructuring of farms, characterized by strong size increases and productivity gains based on a greater reliance on purchases of animal feed. The provision of grazing land has an important role in determining the average costs and farm profitability. In addition, grazing land use permits greater exploitation of economies of scale present in the dairy sector.