In this article we discuss an aspect of economic growth that has not been the subject of much consideration in economic and agrarian history to date: the effect of biological innovations on farming development between the mid nineteenth century and the 1930s. We have focused on dairy farming for two reasons. Firstly, dairy farming played a relevant economic role in a number of European regions during this period. Secondly, one of its products, liquid milk, was probably the most significant food during the early stages of the European nutrition transition. We present new statistical data for the evolution of dairy farming in different Northern European countries as well as Spain, and evaluate the impact of cattle population and milk yields in each case. We also link milk yields and the availability of fodder, but special attention is paid to the breeds kept and techniques for their improvement. The article shows that cattle improvement played a significant role in Central and Northern Europe from the mid nineteenth century, but that this was not the case in Spain. Improvement through inbreeding was soon discarded in Spain, absorbent crossbreeding failed, and the sector became dependent on foreign imports of bulls and cows, first from Switzerland and later from Holland. By taking these factors into consideration we can better understand why the dairy sector in Mediterranean Europe did not really begin until the late nineteenth century and why it stagnated in the wake of the First World War.